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L_0890 | endothermic reactions | T_4412 | All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called exothermic reactions, more energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of endothermic reactions. In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when new bonds form in the products. | text | null |
L_0890 | endothermic reactions | T_4413 | The word endothermic literally means taking in heat. A constant input of energy, often in the form of heat, is needed to keep an endothermic reaction going. This is illustrated in the Figure 1.1. Energy must be constantly added because not enough energy is released when the products form to break more bonds in the reactants. The general equation for an endothermic reaction is: Reactants + Energy Products Note: H represents the change in en- ergy. In endothermic reactions, the temperature of the products is typically lower than the temperature of the reactants. The drop in temperature may be great enough to cause liquids to freeze. Q: Now can you guess how an instant cold pack works? A: Squeezing the cold pack breaks an inner bag of water, and the water mixes with a chemical inside the pack. The chemical and water combine in an endothermic reaction. The energy needed for the reaction to take place comes from the water, which gets colder as the reaction proceeds. | text | null |
L_0890 | endothermic reactions | T_4414 | One of the most important series of endothermic reactions is photosynthesis. In photosynthesis, plants make the simple sugar glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ) in the process. The reactions of photosynthesis are summed up by this chemical equation: 6 CO2 + 6 H2 O C6 H12 O6 + 6 O2 The energy for photosynthesis comes from light. Without light energy, photosynthesis cannot occur. As you can see in the Figure 1.2, plants can get the energy they need for photosynthesis from either sunlight or artificial light. | text | null |
L_0891 | energy | T_4415 | Energy is defined in science as the ability to move matter or change matter in some other way. Energy can also be defined as the ability to do work, which means using force to move an object over a distance. When work is done, energy is transferred from one object to another. For example, when the boy in the Figure 1.1 uses force to swing the racket, he transfers some of his energy to the racket. Q: It takes energy to play tennis. Where does this boy get his energy? A: He gets energy from the food he eats. | text | null |
L_0891 | energy | T_4416 | Because energy is the ability to do work, it is expressed in the same unit that is used for work. The SI unit for both work and energy is the joule (J), or Newton meter (N m). One joule is the amount of energy needed to apply a force of 1 Newton over a distance of 1 meter. For example, suppose the boy in the Figure 1.1 applies 20 Newtons of force to his tennis racket over a distance of 1 meter. The energy needed to do this work is 20 N m, or 20 J. | text | null |
L_0891 | energy | T_4417 | If you think about different sources of energysuch as batteries and the sunyou probably realize that energy can take different forms. For example, when the boy swings his tennis racket, the energy of the moving racket is an example of mechanical energy. To move his racket, the boy needs energy stored in food, which is an example of chemical energy. Other forms of energy include electrical, thermal, light, and sound energy. The different forms of energy can also be classified as either kinetic energy or potential energy. Kinetic energy is the energy of moving matter. Potential energy is energy that is stored in matter. Q: Is the chemical energy in food kinetic energy or potential energy? A: The chemical energy in food is potential energy. It is stored in the chemical bonds that make up food molecules. The stored energy is released when we digest food. Then we can use it for many purposes, such as moving (mechanical energy) or staying warm (thermal energy). Q: What is an example of kinetic energy? A: Anything that is moving has kinetic energy. An example is a moving tennis racket. | text | null |
L_0892 | energy conversion | T_4418 | Gravity is a force, but not like other forces you may know. Gravity is a bit special. You know that a force is a push or pull. If you push a ball, it starts to roll. If you lift a book, it moves upward. Now, imagine you drop a ball. It falls to the ground. Can you see the force pulling it down? That is what makes gravity really cool. It is invisible. Invisible means you cannot see it. But wait, it has even more surprises. Gravity holds planets in place around the Sun. Gravity keeps the Moon from flying off into space. Gravity exerts a force on objects that are not even touching. In fact, gravity can act over very large distances. However, the force does get weaker the farther apart the objects are. | text | null |
L_0892 | energy conversion | T_4419 | You are already very familiar with Earths gravity. It constantly pulls you toward Earths center. What might happen if there was no gravity? You know that the Earth is rotating on its axis. This motion causes our day and night cycle. The Earth also orbits the Sun. All this motion may cause you to fly off the Earth! You can thank gravity for keeping you in place. Gravity keeps us firmly down on the ground. Gravity also pulls on objects that are in the sky. It also pulls on objects that are in space. Meteors and skydivers are pulled down by gravity. Gravity also keeps the moon orbiting the Earth. Without gravity, the moon would float away. It also holds artificial satellites in their orbit. Many of these satellites help to connect the world. They allow you to pick up a phone a call in many parts of the world. You can also thank gravity for all your TV channels. Gravity keeps Earth and the other planets moving around the much more massive Sun. | text | null |
L_0892 | energy conversion | T_4420 | "What goes up must come down." You have probably heard that statement before. At one time this statement was true, but no longer. Since the 1960s, we have sent many spacecraft into space. Some are still traveling away from Earth. So it is possible to overcome gravity. Do you need a giant rocket to overcome gravity? No, you actually overcome gravity every day. Think about when you climb a set of stairs. When you do, you are overcoming gravity. What if you jump on a trampoline? You are overcoming gravity for a few seconds. Everyone can overcome gravity. You just need to apply a force larger than gravity. Think about that the next time you jump into the air. You are overcoming gravity for a brief second. Enjoy it while it lasts. Eventually, gravity will win the battle. | text | null |
L_0892 | energy conversion | T_4421 | 1. What is the traditional definition of gravity? 2. Identify factors that influence the strength of gravity between two objects. | text | null |
L_0892 | energy conversion | T_4422 | By clicking a link below, you will leave the CK-12 site and open an external site in a new tab. This page will remain open in the original tab. | text | null |
L_0893 | energy level | T_4423 | Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons may be found. Electrons are tiny, negatively charged particles in an atom that move around the positive nucleus at the center. Energy levels are a little like the steps of a staircase. You can stand on one step or another but not in between the steps. The same goes for electrons. They can occupy one energy level or another but not the space between energy levels. The model in the Figure 1.1 shows the first four energy levels of an atom. Electrons in energy level I (also called energy level K) have the least amount of energy. As you go farther from the nucleus, electrons at higher levels have more energy, and their energy increases by a fixed, discrete amount. Electrons can jump from a lower to the next higher energy level if they absorb this amount of energy. Conversely, if electrons jump from a higher to a lower energy level, they give off energy, often in the form of light. This explains the fireworks pictured above. When the fireworks explode, electrons gain energy and jump to higher energy levels. When they jump back to their original energy levels, they release the energy as light. Different atoms have different arrangements of electrons, so they give off light of different colors. Q: In the atomic model Figure 1.1, where would you find electrons that have the most energy? A: Electrons with the most energy would be found in energy level IV. | text | null |
L_0893 | energy level | T_4424 | The smallest atoms are hydrogen atoms. They have just one electron orbiting the nucleus. That one electron is in the first energy level. Bigger atoms have more electrons. Electrons are always added to the lowest energy level first until it has the maximum number of electrons possible. Then electrons are added to the next higher energy level until that level is full, and so on. How many electrons can a given energy level hold? The maximum numbers of electrons possible for the first four energy levels are shown in the Figure 1.1. For example, energy level I can hold a maximum of two electrons, and energy level II can hold a maximum of eight electrons. The maximum number depends on the number of orbitals at a given energy level. An orbital is a volume of space within an atom where an electron is most likely to be found. As you can see by the images in the Figure 1.2, some orbitals are shaped like spheres (S orbitals) and some are shaped like dumbbells (P orbitals). There are other types of orbitals as well. Regardless of its shape, each orbital can hold a maximum of two electrons. Energy level I has just one orbital, so two electrons will fill this energy level. Energy level II has four orbitals, so it takes eight electrons to fill this energy level. Q: Energy level III can hold a maximum of 18 electrons. How many orbitals does this energy level have? A: At two electrons per orbital, this energy level must have nine orbitals. | text | null |
L_0893 | energy level | T_4425 | Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can | text | null |
L_0893 | energy level | T_4425 | Electrons in the outermost energy level of an atom have a special significance. These electrons are called valence electrons, and they determine many of the properties of an atom. An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so heliums only energy level is full. This makes helium a very stable element. In other words, its atoms are unlikely to react with other atoms. Consider the elements fluorine and lithium, modeled in the Figure 1.3. Fluorine has seven of eight possible electrons in its outermost energy level, which is energy level II. It would be more stable if it had one more electron because this would fill its outermost energy level. Lithium, on the other hand, has just one of eight possible electrons in its outermost energy level (also energy level II). It would be more stable if it had one less electron because it would have a full outer energy level (now energy level I). Both fluorine and lithium are highly reactive elements because of their number of valence electrons. Fluorine will readily gain one electron and lithium will just as readily give up one electron to become more stable. In fact, lithium and fluorine will react together as shown in the Figure 1.4. When the two elements react, lithium transfers its one extra electron to fluorine. Q: A neon atom has ten electrons. How many electrons does it have in its outermost energy level? How stable do you think a neon atom is? A: A neon atom has two electrons in energy level I and its remaining eight electrons in energy level II, which can | text | null |
L_0894 | enzymes as catalysts | T_4426 | Chemical reactions constantly occur inside the cells of living things. However, under the conditions inside cells, most biochemical reactions would occur too slowly to maintain life. Thats where enzymes come in. Enzymes are catalysts in living things. Like other catalysts, they speed up chemical reactions. Enzymes are proteins that are synthesized in the cells that need them, based on instructions encoded in the cells DNA. | text | null |
L_0894 | enzymes as catalysts | T_4427 | Enzymes increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants to start reacting. One way this can happen is modeled in the Figure 1.1. Enzymes arent changed or used up in the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Each enzyme is highly specific for the particular reaction is catalyzes, so enzymes are very effective. A reaction that would take many years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very efficient, so waste products rarely form. Q: This model of enzyme action is called the lock-and-key model. Explain why. A: The substrates (reactants) fit precisely into the active site of the enzyme like a key into a lock. Being brought together in the enzyme in this way helps the reactants react more easily. After the product is formed, it is released by the enzyme. The enzyme is now ready to pick up more reactants and catalyze another reaction. Click image to the left or use the URL below. URL: | text | null |
L_0894 | enzymes as catalysts | T_4428 | More than 1000 different enzymes are necessary for human life. Many enzymes are needed for the digestion of food. Two examples are amylase and pepsin. Both are described in the Figure 1.2. | text | null |
L_0897 | exothermic reactions | T_4435 | All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new bonds form in products. In some chemical reactions, called endothermic reactions, less energy is released when new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of exothermic reactions. In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new bonds form in the products. | text | null |
L_0897 | exothermic reactions | T_4436 | The word exothermic means releasing heat. Energy, often in the form of heat, is released as an exothermic reaction proceeds. This is illustrated in the Figure 1.1. The general equation for an exothermic reaction is: Reactants Products + Energy If the energy produced in an exothermic reaction is released as heat, it results in a rise in temperature. As a result, the products are likely to be warmer than the reactants. Note: H represents the change in en- ergy. Q: You turn on the hot water faucet, and hot water pours out. How does the water get hot? Do you think that an exothermic reaction might be involved? A: A hot water heater increases the temperature of water in most homes. Many hot water heaters burn a fuel such as natural gas. The burning fuel causes the water to get hot because combustion is an exothermic reaction. | text | null |
L_0897 | exothermic reactions | T_4437 | All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines with oxygen. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in the Figure 1.2. The combustion of wood is an exothermic reaction that releases a lot of energy as heat and light. You can see the light energy the fire is giving off. If you were standing near the fire, you would also feel its heat. | text | null |
L_0898 | external combustion engines | T_4438 | A combustion engine is a complex machine that burns fuel to produce thermal energy and then uses the thermal energy to do work. There are two types of combustion engines: external and internal. A steam engine is an external combustion engine. | text | null |
L_0898 | external combustion engines | T_4439 | An external combustion engine burns fuel externally, or outside the engine. The burning fuel releases thermal energy, which is used to heat water and change it to steam. The pressure of the steam moves a piston back and forth inside a cylinder. The kinetic energy of the moving piston can be used to turn a vehicles wheels, a turbine, or other mechanical device. The Figure 1.1 explains in greater detail how this type of engine works. Q: What type of energy does the piston have when it moves back and forth inside the cylinder? A: Like anything else that is moving, the moving piston has kinetic energy. | text | null |
L_0899 | ferromagnetic material | T_4440 | Magnetism is the ability of a material to be attracted by a magnet and to act as a magnet. Magnetism is due to the movement of electrons within atoms of matter. When electrons spin around the nucleus of an atom, it causes the atom to become a tiny magnet, with north and south poles and a magnetic field. In most materials, the north and south poles of atoms point in all different directions, so overall the material is not magnetic. Examples of nonmagnetic materials include wood, glass, plastic, paper, copper, and aluminum. These materials are not attracted to magnets and cannot become magnets. In other materials, there are regions where the north and south poles of atoms are all lined up in the same direction. These regions are called magnetic domains. Generally, the magnetic domains point in different directions, so the material is still not magnetic. However, the material can be magnetized (made into a magnet) by placing it in a magnetic field. When this happens, all the magnetic domains line up, and the material becomes a magnet. You can see this in the Figure 1.1. Materials that can be magnitized are called ferromagnetic materials. They include iron, cobalt, and nickel. | text | null |
L_0899 | ferromagnetic material | T_4441 | Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? | text | null |
L_0899 | ferromagnetic material | T_4441 | Materials that have been magnetized may become temporary or permanent magnets. If you bring a bar magnet close to pile of paper clips, the paper clips will become temporarily magnetized, as all their magnetic domains line up. As a result, the paper clips will stick to the magnet and also to each other (see the Figure 1.2). However, if you remove the paper clips from the bar magnets magnetic field, their magnetic domains will no longer align. As a result, the paper clips will no longer be magnetized or stick together. If you stroke an iron nail with a bar magnet, the nail will become a permanent (or at least long-lasting) magnet. You can see how its done in the Figure 1.3. The nails magnetic domains will remain aligned even after you remove the nail from the magnetic field of the bar magnet. Q: Even permanent magnets can be demagnetized if they are dropped or heated to high temperatures. Can you explain why? | text | null |
L_0899 | ferromagnetic material | T_4442 | Some materials are natural permanent magnets. The most magnetic material in nature is the mineral magnetite, also called lodestone (see Figure 1.4). The magnetic domains of magnetite naturally align with Earths axis. The picture on the left shows a chunk of magnetite attracting small bits of iron. The magnetite spoon compass shown on the right dates back about 2000 years and comes from China. The handle of the spoon always points north. Clearly, the magnetic properties of magnetite have been recognized for thousands of years. | text | null |
L_0901 | force | T_4445 | Force is defined as a push or pull acting on an object. There are several fundamental forces in the universe, including the force of gravity, electromagnetic force, and weak and strong nuclear forces. When it comes to the motion of everyday objects, however, the forces of interest include mainly gravity, friction, and applied force. Applied force is force that a person or thing applies to an object. Q: What forces act on Carsons scooter? A: Gravity, friction, and applied forces all act on Carsons scooter. Gravity keeps pulling both Carson and the scooter toward the ground. Friction between the wheels of the scooter and the ground prevent the scooter from sliding but also slow it down. In addition, Carson applies forces to his scooter to control its speed and direction. | text | null |
L_0901 | force | T_4446 | Forces cause all motions. Everytime the motion of an object changes, its because a force has been applied to it. Force can cause a stationary object to start moving or a moving object to change its speed or direction or both. A change in the speed or direction of an object is called acceleration. Look at Carsons brother Colton in the Figure starts the scooter moving in the opposite direction. The harder he pushes against the ground, the faster the scooter will go. How much an object accelerates when a force is applied to it depends not only on the strength of the force but also on the objects mass. For example, a heavier scooter would be harder to accelerate. Colton would have to push with more force to start it moving and move it faster. Q: What units do you think are used to measure force? A: The SI unit for force is the Newton (N). A Newton is the force needed to cause a mass of 1 kilogram to accelerate at 1 m/s2 , so a Newton equals 1 kg m/s2 . The Newton was named for the scientist Sir Isaac Newton, who is famous for his laws of motion and gravity. | text | null |
L_0901 | force | T_4447 | Force is a vector, or a measure that has both size and direction. For example, Colton pushes on the ground in the opposite direction that the scooter moves, so thats the direction of the force he is applies. He can give the scooter a strong push or a weak push. Thats the size of the force. Like other vectors, a force can be represented with an arrow. You can see some examples in the Figure 1.2. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. Q: How could you use arrows to represent the forces that start Coltons scooter moving? A: Colton pushes against the ground behind him (to the right in the Figure 1.1). The ground pushes back with equal force to the left, causing the scooter to move in that direction. Force arrows A and B in example 2 in the Figure 1.1) could represent these forces. | text | null |
L_0902 | forms of energy | T_4448 | Energy, or the ability to cause changes in matter, can exist in many different forms. Energy can also change from one form to another. The photo above of the guitar player represents six forms of energy: mechanical, chemical, electrical, light, thermal, and sound energy. Another form of energy is nuclear energy. Q: Can you find the six different forms of energy in the photo of the guitar player (See opening image)? A: The guitarist uses mechanical energy to pluck the strings of the guitar. He gets the energy he needs to perform from chemical energy in food he ate earlier in the day. The stage lights use electrical energy, which they change to light energy and thermal energy (commonly called heat). The guitar produces sound energy when the guitarist plucks the strings. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0902 | forms of energy | T_4449 | The different forms of energy are defined and illustrated below. 1. Mechanical energy is the energy of movement. It is found in objects that are moving or have the potential to move. 2. Chemical energy is energy that is stored in the bonds between the atoms of compounds. If the bonds are broken, the energy is released and can be converted to other forms of energy. This portable guitar amplifier can run on batteries. Batteries store chemical energy and change it to electrical energy. 3. Electrical energy is the energy of moving electrons. Electrons flow through wires to create electric current. 4. Electromagnetic energy is energy that travels through space as electrical and magnetic waves. The light flooding the stage in the Figure 1.3 is one type of electromagnetic energy. Other types include radio waves, microwaves, X rays, and gamma rays. 5. Thermal energy is the energy of moving atoms of matter. All matter has thermal energy because atoms of all matter are constantly moving. An object with more mass has greater thermal energy than an object with less mass because it has more atoms. Why is this jogger sweating so much? His sweat is soaking up his shirt because he has so much thermal energy. Jogging is hot work because of the heat from the sun and the hard work he puts into his run. 6. Sound energy is a form of mechanical energy that starts with a vibration in matter. For example, the singers voice 7. Nuclear energy is energy that is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. The energy can be released in nuclear power plants by splitting nuclei apart. It is also released when unstable (radioactive) nuclei break down, or decay. Q: The fans at a rock concert also produce or use several forms of energy. What are they? A: The fans see the concert because of electromagnetic energy (light) that enters their eyes from the well-lit musicians on stage. They hear the music because of the sound energy that reaches their ears from the amplifiers. They use mechanical energy when they clap their hands and jump from their seats in excitement. Their bodies generate thermal energy, using the chemical energy stored in food they have eaten. | text | null |
L_0904 | frequency and pitch of sound | T_4452 | How high or low a sound seems to a listener is its pitch. Pitch, in turn, depends on the frequency of sound waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. High-pitched sounds, like the sounds of the piccolo in the Figure 1.1, have high-frequency waves. Low-pitched sounds, like the sounds of the tuba Figure 1.1, have low-frequency waves. | text | null |
L_0904 | frequency and pitch of sound | T_4453 | The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. | text | null |
L_0904 | frequency and pitch of sound | T_4453 | The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. Sounds with frequencies below 20 hertz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 hertz are called ultrasound. Ultrasound is too high-pitched for humans to hear. Some other animals can hear sounds in the ultrasound range. For example, dogs can hear sounds with frequencies as high as 50,000 Hz. You may have seen special whistles that dogsbut not peoplecan hear. The whistles produce sounds with frequencies too high for the human ear to detect. Other animals can hear even higher-frequency sounds. Bats, like the one pictured in the Figure 1.2, can hear sounds with frequencies higher than 100,000 Hz! Q: Bats use ultrasound to navigate in the dark. Can you explain how? A: Bats send out ultrasound waves, which reflect back from objects ahead of them. They sense the reflected sound waves and use the information to detect objects they cant see in the dark. This is how they avoid flying into walls and trees and also how they find flying insects to eat. | text | null |
L_0905 | friction | T_4454 | Friction is a force that opposes motion between any surfaces that are touching. Friction can work for or against us. For example, putting sand on an icy sidewalk increases friction so you are less likely to slip. On the other hand, too much friction between moving parts in a car engine can cause the parts to wear out. Other examples of friction are illustrated in the two Figures 1.1 and 1.2. | text | null |
L_0905 | friction | T_4455 | Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure 1.3. The aluminum foil These photos show two ways that friction is useful These photos show two ways that friction can cause problems is so smooth that its shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction. | text | null |
L_0905 | friction | T_4455 | Friction occurs because no surface is perfectly smooth. Even surfaces that look smooth to the unaided eye make look rough or bumpy when viewed under a microscope. Look at the metal surfaces in the Figure 1.3. The aluminum foil These photos show two ways that friction is useful These photos show two ways that friction can cause problems is so smooth that its shiny. However, when highly magnified, the surface of metal appears to be very bumpy. All those mountains and valleys catch and grab the mountains and valleys of any other surface that contacts the metal. This creates friction. | text | null |
L_0905 | friction | T_4456 | Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. You cant slide as far across ice with shoes as you can on the blades of skates (see Figure 1.4). The rougher surface of the soles of the shoes causes more friction and slows you down. Q: Heavier objects also have more friction. Can you explain why? A: Heavier objects press together with greater force, and this causes greater friction between them. Did you ever try to furniture across the floor? Its harder to overcome friction between a heavier piece of furniture and the floor than between lighter pieces and the floor. | text | null |
L_0905 | friction | T_4456 | Rougher surfaces have more friction between them than smoother surfaces. Thats why we put sand on icy sidewalks and roads. You cant slide as far across ice with shoes as you can on the blades of skates (see Figure 1.4). The rougher surface of the soles of the shoes causes more friction and slows you down. Q: Heavier objects also have more friction. Can you explain why? A: Heavier objects press together with greater force, and this causes greater friction between them. Did you ever try to furniture across the floor? Its harder to overcome friction between a heavier piece of furniture and the floor than between lighter pieces and the floor. | text | null |
L_0905 | friction | T_4457 | You know that friction produces heat. Thats why rubbing your hands together makes them warmer. But do you know why? Friction causes the molecules on rubbing surfaces to move faster, so they have more energy. This gives them a higher temperature, and they feel warmer. Heat from friction can be useful. It not only warms your hands. It also lets you light a match as shown in the Figure 1.5. On the other hand, heat from friction between moving parts inside a car engine can be a big problem. It can cause the car to overheat. Q: How is friction reduced between the moving parts inside a car engine? A: To reduce friction, oil is added to the engine. The oil coats the surfaces of the moving parts and makes them slippery. They slide over each other more easily, so there is less friction. | text | null |
L_0906 | fundamental particles | T_4458 | Scientists have long wanted to find the most basic building blocks of the universe. They asked, what are the fundamental particles of matter that cannot be subdivided into smaller, simpler particles, and what holds these particles together? The quest for fundamental particles began thousands of years ago. Scientists thought they had finally found them when John Dalton discovered the atom in 1803 (see the timeline in Table 1.1). The word atom means indivisible, and Dalton thought that the atom could not be divided into smaller, simpler particles. Year Discovery Year 1803 Discovery John Dalton discovers the atom. 1897 J.J. Thomson discovers the electron, the first lepton to be discovered. 1905 Albert Einstein discovers the photon, the first boson to be discovered. 1911 Ernest Rutherford discovers the proton, the first particle to be discovered in the nucleus of the atom. Year 1932 Discovery James Chadwick discovers the neutron, another particle in the nucleus. 1964 Murray Gell-Mann proposes the existence of quarks, the fundamental particles that make up protons and neutrons. 1964-present Through the research of many scientists, many other fundamental particles (except gravitons) are shown to exist. For almost 100 years after Dalton discovered atoms, they were accepted as the fundamental particles of matter. But starting in the late 1890s with the discovery of electrons, particles smaller and simpler than atoms were identified. Within a few decades, protons and neutrons were also discovered. Ultimately, hundreds of subatomic particles were found. | text | null |
L_0906 | fundamental particles | T_4459 | Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of matter called quarks. Scientists theorize that leptons and quarks are held together by yet another type of fundamental particles called bosons. All three types of fundamental particlesleptons, quarks, and bosonsare described below. The following Figure 1.1 shows the variety of particles of each type. There are six types of quarks. In ordinary matter, virtually all quarks are of the types called up and down quarks. All quarks have mass, and they have an electric charge of either +2/3 or -1/3. For example, up quarks have a charge of +2/3, and down quarks have a charge of -1/3. Quarks also have a different type of charge, called color charge, although it has nothing to do with the colors that we see. Quarks are never found alone but instead always occur in groups of two or three quarks. There are also six types of leptons, including electrons. Leptons have an electric charge of either -1 or 0. Electrons, for example, have a charge of -1. Leptons have mass, although the mass of electrons is extremely small. There are four known types of bosons, which are force-carrying particles. Each of these bosons carries a different fundamental force between interacting particles. In addition, there is a particle which may exist, called the "Higgs Boson", which gives objects the masses they have. Some types of bosons have mass; others are massless. Bosons have an electric charge of +1, -1, or 0. Q: Protons consist of three quarks: two up quarks and one down quark. Neutrons also consist of three quarks: two down quarks and one up quark. Based on this information, what is the total electric charge of a proton? Of a neutron? A: These combinations of quarks give protons a total electric charge of +1 (2/3 + 2/3 - 1/3 = 1) and neutrons a total electric charge of 0 (2/3 - 1/3 - 1/3 = 0). | text | null |
L_0906 | fundamental particles | T_4460 | The interactions of matter particles are subject to four fundamental forces: gravity, electromagnetic force, weak nuclear force, and strong nuclear force. All of these forces are thought to be transmitted by bosons, the force- carrying fundamental particles. The different types of bosons and the forces they carry are shown in Table 1.2. Consider the examples of gluons, the bosons that carry the strong nuclear force. A continuous exchange of gluons between quarks binds them together in both protons and neutrons. Note that force-carrying particles for gravity (gravitons) have not yet been found. Type of Bosons Gluons Fundamental Force They Carry strong nuclear force Particles They Affect quarks Distance over Which They Carry Force only within the nucleus Type of Bosons W bosons Z bosons Photons Gravitons (hypothetical) Fundamental Force They Carry weak nuclear force Particles They Affect leptons and quarks Distance over Which They Carry Force only within the nucleus electromagnetic force force of gravity leptons and quarks leptons and quarks all distances all distances Q: Which type of boson carries force between the negative electrons and positive protons of an atom? A: Photons carry electromagnetic force. They are responsible for the force of attraction or repulsion between all electrically charged matter, including the force of attraction between negative electrons and positive protons in an atom. Q: Gravitons have not yet been discovered so they have only been hypothesized to exist. What evidence do you think leads scientists to think that these hypothetical particles affect both leptons and quarks and that they carry force over all distances? A: Gravity is known to affect all matter that has mass, and both quarks and leptons have mass. Gravity is also known to work over long as well as short distances. For example, Earths gravity keeps you firmly planted on the ground and also keeps the moon orbiting around the planet. | text | null |
L_0906 | fundamental particles | T_4461 | Based on their knowledge of subatomic particles, scientists have developed a theory called the standard model to explain all the matter in the universe and how it is held together. The model includes only the fundamental particles in the Table 1.2. No other particles are needed to explain all kinds of matter. According to the model, all known matter consists of quarks and leptons that interact by exchanging bosons, which transmit fundamental forces. The standard model is a good theory because all of its predictions have been verified by experimental data. However, the model doesnt explain everything, including the force of gravity and why matter has mass. Scientists continue to search for evidence that will allow them to explain these aspects of force and matter as well. | text | null |
L_0907 | gamma decay | T_4462 | Gamma rays are electromagnetic waves. Electromagnetic waves are waves of electric and magnetic energy that travel through space at the speed of light. The energy travels in tiny packets of energy, called photons. Photons of gamma energy are called gamma particles. Other electromagnetic waves include microwaves, light rays, and X rays. Gamma rays have the greatest amount of energy of all electromagnetic waves. Click image to the left or use the URL below. URL: | text | null |
L_0907 | gamma decay | T_4463 | Gamma rays are produced when radioactive elements decay. Radioactive elements are elements with unstable nuclei. To become more stable, the nuclei undergo radioactive decay. In this process, the nuclei give off energy and may also emit charged particles of matter. Types of radioactive decay include alpha, beta, and gamma decay. In alpha and beta decay, both particles and energy are emitted. In gamma decay, only energy, in the form of gamma rays, is emitted. Alpha and beta decay occur when a nucleus has too many protons or an unstable ratio of protons to neutrons. When the nucleus emits a particle, it gains or loses one or two protons, so the atom becomes a different element. Gamma decay, in contrast, occurs when a nucleus is in an excited state and has too much energy to be stable. This often happens after alpha or beta decay has occurred. Because only energy is emitted during gamma decay, the number of protons remains the same. Therefore, an atom does not become a different element during this type of decay. Q: The Figure 1.1 shows how helium-3 (He-3) decays by emitting a gamma particle. How can you tell that the atom is still the same element after gamma decay occurs? A: The nucleus of the atom has two protons (red) before the reaction occurs. After the nucleus emits the gamma particle, it still has two protons, so the atom is still the same element. | text | null |
L_0907 | gamma decay | T_4464 | Gamma rays are the most dangerous type of radiation. They can travel farther and penetrate materials more deeply than can the charged particles emitted during alpha and beta decay. Gamma rays can be stopped only by several centimeters of lead or several meters of concrete. Its no surprise that they can penetrate and damage cells deep inside the body. | text | null |
L_0908 | gamma rays | T_4465 | Electromagnetic waves transfer energy across space as well as through matter. They vary in their wavelengths and frequencies, and higher-frequency waves have more energy. The full range of wavelengths of electromagnetic waves, shown in the Figure 1.1, is called the electromagnetic spectrum. | text | null |
L_0908 | gamma rays | T_4466 | As you can see in the Figure 1.1, gamma rays have the shortest wavelengths and highest frequencies of all electromagnetic waves. Their wavelengths are shorter than the diameter of atomic nuclei, and their frequencies are greater than 1019 hertz (Hz). Thats 10 quadrillion waves per second! Because of their high frequencies, gamma rays are also the most energetic of all electromagnetic waves. | text | null |
L_0908 | gamma rays | T_4467 | Gamma rays are given off by radioactive atoms and nuclear explosions. They are also given off by the sun and other stars, as well as by collapsing stars in gamma ray bursts. Fortunately, gamma rays from space are absorbed by Earths atmosphere before they can reach the surface. Q: Predict how gamma rays might affect living things on Earth if they werent absorbed by the atmosphere. A: Gamma rays would destroy most living things on Earth because they have so much energy. | text | null |
L_0908 | gamma rays | T_4468 | The extremely high energy of gamma rays allows them to penetrate just about anything. They can even pass through bones and teeth. This makes gamma rays very dangerous. They can destroy living cells, produce gene mutations, and cause cancer. Ironically, the deadly effects of gamma rays can be used to treat cancer. In this type of treatment, a medical device sends out focused gamma rays that target cancerous cells. The gamma rays kill the cells and destroy the cancer. | text | null |
L_0910 | gravity | T_4472 | Gravity has traditionally been defined as a force of attraction between things that have mass. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. Gravity can act between objects that are not even touching. In fact, gravity can act over very long distances. However, the farther two objects are from each other, the weaker is the force of gravity between them. Less massive objects also have less gravity than more massive objects. | text | null |
L_0910 | gravity | T_4473 | You are already very familiar with Earths gravity. It constantly pulls you toward the center of the planet. It prevents you and everything else on Earth from being flung out into space as the planet spins on its axis. It also pulls objects that are above the surfacefrom meteors to skydiversdown to the ground. Gravity between Earth and the moon and between Earth and artificial satellites keeps all these objects circling around Earth. Gravity also keeps Earth and the other planets moving around the much more massive sun. Q: There is a force of gravity between Earth and you and also between you and all the objects around you. When you drop a paper clip, why doesnt it fall toward you instead of toward Earth? A: Earth is so much more massive than you that its gravitational pull on the paper clip is immensely greater. | text | null |
L_0910 | gravity | T_4474 | Weight measures the force of gravity pulling downward on an object. The SI unit for weight, like other forces, is the Newton (N). On Earth, a mass of 1 kilogram has a weight of about 10 Newtons because of the pull of Earths gravity. On the moon, which has less gravity, the same mass would weigh less. Weight is measured with a scale, like the spring scale shown in the Figure 1.1. The scale measures the force with which gravity pulls an object downward. To delve a little deeper into weight and gravity, watch this video: Click image to the left or use the URL below. URL: | text | null |
L_0910 | gravity | T_4475 | At the following URL, read about gravity and tides. Watch the animation and look closely at the diagrams. Then answer the questions below. 1. 2. 3. 4. 5. What causes tides? Which has a greater influence on tides, the moon or the sun? Why? Why is there a tidal bulge of water on the opposite side of Earth from the moon? When are tides highest? What causes these tides to be highest? When are tides lowest? What causes these tides to be lowest? | text | null |
L_0911 | groups with metalloids | T_4476 | Groups 13-16 of the periodic table (orange in the Figure 1.1) are the only groups that contain elements classified as metalloids. Unlike other groups of the periodic table, which contain elements in just one class, groups 13-16 contain elements in at least two different classes. In addition to metalloids, they also contain metals, nonmetals, or both. Groups 13-16 fall between the transition metals (in groups 3-12) and the nonmetals called halogens (in group 17). | text | null |
L_0911 | groups with metalloids | T_4477 | Metalloids are the smallest class of elements, containing just six members: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Metalloids have some properties of metals (elements that can conduct electricity) and some properties of nonmetals (elements that cannot conduct electricity). For example, most metalloids can conduct electricity, but not as well as metals. Metalloids also tend to be shiny like metals, but brittle like nonmetals. Chemically, metalloids may behave like metals or nonmetals, depending on their number of valence electrons. Q: Why does the chemical behavior of an element depend on its number of valence electrons? A: Valence electrons are the electrons in an atoms outer energy level that may be involved in chemical reactions with other atoms. | text | null |
L_0911 | groups with metalloids | T_4478 | Group 13 of the periodic table is also called the boron group because boron (B) is the first element at the top of the group (see Figure 1.2). Boron is also the only metalloid in this group. The other four elements in the groupaluminum (Al), gallium (Ga), indium (In), and thallium (Tl)are all metals. Group 13 elements have three valence electrons and are fairly reactive. All of them are solids at room temperature. | text | null |
L_0911 | groups with metalloids | T_4479 | Group 14 of the periodic table is headed by the nonmetal carbon (C), so this group is also called the carbon group. Carbon is followed by silicon (Si) and germanium (Ge) (Figure 1.3), which are metalloids, and then by tin (Sn) and lead (Pb), which are metals. Group 14 elements group have four valence electrons, so they generally arent very reactive. All of them are solids at room temperature. | text | null |
L_0911 | groups with metalloids | T_4480 | Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) (Figure 1.4) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they Germanium is a brittle, shiny, silvery- white metalloid. Along with silicon, it is used to make the tiny electric cir- cuits on computer chips. It is also used to make fiber optic cableslike the one pictured herethat carry telephone and other communication signals. vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas. | text | null |
L_0911 | groups with metalloids | T_4480 | Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) (Figure 1.4) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they Germanium is a brittle, shiny, silvery- white metalloid. Along with silicon, it is used to make the tiny electric cir- cuits on computer chips. It is also used to make fiber optic cableslike the one pictured herethat carry telephone and other communication signals. vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas. | text | null |
L_0911 | groups with metalloids | T_4481 | Group 16 of the periodic table is also called the oxygen group. The first three elementsoxygen (O), sulfur (S), and selenium (Se)are nonmetals. They are followed by tellurium (Te) (Figure 1.5), a metalloid, and polonium (Po), a metal. All group 16 elements have six valence electrons and are very reactive. Oxygen is a gas at room temperature, and the other elements in the group are solids. Q: With six valence electrons, group 16 elements need to attract two electrons from another element to have a stable electron arrangement of eight valence electrons. Which group of elements in the periodic table do you think might The most common form of the metalloid arsenic is gray and shiny. Arsenic is extremely toxic, so it is used as rat poison. Surprisingly, we need it (in tiny amounts) for normal growth and a healthy nervous system. form compounds with elements in group 16? A: Group 2 elements, called the alkaline Earth metals, form compounds with elements in the oxygen group. Thats because group 2 elements have two valence electrons that they are eager to give up. An example of a group 2 and group 6 compound is calcium oxide (CaO). | text | null |
L_0911 | groups with metalloids | T_4481 | Group 16 of the periodic table is also called the oxygen group. The first three elementsoxygen (O), sulfur (S), and selenium (Se)are nonmetals. They are followed by tellurium (Te) (Figure 1.5), a metalloid, and polonium (Po), a metal. All group 16 elements have six valence electrons and are very reactive. Oxygen is a gas at room temperature, and the other elements in the group are solids. Q: With six valence electrons, group 16 elements need to attract two electrons from another element to have a stable electron arrangement of eight valence electrons. Which group of elements in the periodic table do you think might The most common form of the metalloid arsenic is gray and shiny. Arsenic is extremely toxic, so it is used as rat poison. Surprisingly, we need it (in tiny amounts) for normal growth and a healthy nervous system. form compounds with elements in group 16? A: Group 2 elements, called the alkaline Earth metals, form compounds with elements in the oxygen group. Thats because group 2 elements have two valence electrons that they are eager to give up. An example of a group 2 and group 6 compound is calcium oxide (CaO). | text | null |
L_0912 | halogens | T_4482 | Halogens are highly reactive nonmetallic elements in group 17 of the periodic table. As you can see in the periodic table 1.1, the halogens include the elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). All of them are relatively common on Earth except for astatine. Astatine is radioactive and rapidly decays to other, more stable elements. As a result, it is one of the least common elements on Earth. Q: Based on their position in the periodic table from the Figure 1.1, how many valence electrons do you think halogens have? A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1-2 and 13-18 (numbered 3-0 in the periodic table above.) Therefore, halogens have seven valence electrons. | text | null |
L_0912 | halogens | T_4483 | The halogens are among the most reactive of all elements, although reactivity declines from the top to the bottom of the halogen group. Because all halogens have seven valence electrons, they are eager to gain one more electron. Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally eager to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive. You can see some examples in the video below. (Warning: Dont try any of these reactions at home!) Click image to the left or use the URL below. URL: | text | null |
L_0912 | halogens | T_4484 | The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the Figure 1.2. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points. | text | null |
L_0912 | halogens | T_4485 | Most halogens have a variety of important uses. A few are described in the Figure 1.3. Q: Can you relate some of these uses of halogens to the properties of these elements? A: The ability of halogens to kill germs and bleach clothes relates to their highly reactive nature. | text | null |
L_0913 | hearing and the ear | T_4486 | Sound is a form of energy that travels in waves through matter. The ability to sense sound energy and perceive sound is called hearing. The organ that we use to sense sound energy is the ear. Almost all the structures in the ear are needed for this purpose. Together, they gather sound waves, amplify the waves, and change their kinetic energy to electrical signals. The electrical signals travel to the brain, which interprets them as the sounds we hear. The Figure 1.1 shows the three main parts of the ear: the outer, middle, and inner ear. It also shows the specific structures in each part of the ear. | text | null |
L_0913 | hearing and the ear | T_4487 | The outer ear includes the pinna, ear canal, and eardrum. The pinna is the only part of the ear that extends outward from the head. Its position and shape make it good at catching sound waves and funneling them into the ear canal. The ear canal is a tube that carries sound waves into the ear. The sound waves travel through the air inside the ear canal to the eardrum. The eardrum is like the head of a drum. It is a thin membrane stretched tight across the end of the ear canal. The eardrum vibrates when sound waves strike it, and it sends the vibrations on to the middle ear. Q: How might cupping his hands behind his ears help the boy pictured in the opening image hear better? A: His hands might help the pinna of his ears catch sound waves and direct them into the ear canal. | text | null |
L_0913 | hearing and the ear | T_4488 | The middle ear contains three tiny bones (ossicles) called the hammer, anvil, and stirrup. If you look at these bones in the Figure 1.1, you might notice that they resemble the objects for which they are named. The three bones transmit vibrations from the eardrum to the inner ear. The arrangement of the three bones allows them to work together as a lever that increases the amplitude of the waves as they pass to the inner ear. Q: Wave amplitude is the maximum distance particles of matter move when a wave passes through them. Why would amplifying the sound waves as they pass through the middle ear improve hearing? A: Amplified sound waves have more energy. This increases the intensity and loudness of the sounds, so they are easier to hear. | text | null |
L_0913 | hearing and the ear | T_4489 | The stirrup in the middle ear passes the amplified sound waves to the inner ear through the oval window. When the oval window vibrates, it causes the cochlea to vibrate as well. The cochlea is a shell-like structure that is full of fluid and lined with nerve cells called hair cells. Each hair cell has many tiny hairs, as you can see in the magnified image 1.2. When the cochlea vibrates, it causes waves in the fluid inside. The waves bend the hairs on the hair cells, and this triggers electrical impulses. The electrical impulses travel to the brain through nerves. Only after the nerve impulses reach the brain do we hear the sound. | text | null |
L_0914 | hearing loss | T_4490 | The ear is a complex organ that senses sound energy so we can hear. Hearing is the ability to sense sound energy and perceive sound. All of the structures of the ear that are involved in hearing must work well for a person to have normal hearing. Damage to any of the structures, through illness or injury, may cause hearing loss. Total hearing loss is called deafness. | text | null |
L_0914 | hearing loss | T_4491 | The most common cause of hearing loss is exposure to loud sounds. Loud sounds can damage hair cells inside the ears. Hair cells change sound waves to electrical signals that the brain can interpret as sounds. Louder sounds, which have greater intensity than softer sounds, can damage hair cells more quickly than softer sounds. You can see the relationship between sound intensity, exposure time, and hearing loss in the following Figure 1.1. The intensity of sounds is measured in decibels (dB). Q: What is the maximum amount of time you should be exposed to a sound as intense as 100 dB? What might make a sound this intense? A: You should be exposed to a 100-dB sound for no longer than 15 minutes. An example of a sound this intense is the sound of a car horn. | text | null |
L_0914 | hearing loss | T_4492 | Hearing loss caused by loud sounds is permanent. However, this type of hearing loss can be prevented by protecting the ears from loud sounds. People who work in jobs that expose them to loud sounds must wear hearing protectors. Examples include construction workers who work around loud machinery for many hours each day. But anyone exposed to loud sounds for longer than the permissible exposure time should wear hearing protectors. Many home and yard chores and even recreational activities are loud enough to cause hearing loss if people are exposed to them for too much time. You can see examples in the Figure 1.2. | text | null |
L_0914 | hearing loss | T_4493 | You can see two different types of hearing protectors in the Figure 1.3. Earplugs are simple hearing protectors that just muffle sounds by partially blocking all sound waves from entering the ears. This type of hearing protector is suitable for lower noise levels, such as the noise of a lawnmower or snowmobile. Electronic ear protectors work differently. They identify high-amplitude sound waves and send sound waves through them in the opposite direction. This causes destructive interference with the waves, which reduces their amplitude to zero or nearly zero. This changes even the loudest sounds to just a soft hiss. Sounds that people need to hear, such as the voices of co-workers, are not interfered with in this way and may be amplified instead so they can be heard more clearly. This type of hearing protector is recommended for higher noise levels and situations where its important to be able to hear lower-decibel sounds. | text | null |
L_0915 | heat | T_4494 | Heat is the transfer of thermal energy between substances. Thermal energy is the kinetic energy of moving particles of matter, measured by their temperature. Thermal energy always moves from matter with greater thermal energy to matter with less thermal energy, so it moves from warmer to cooler substances. You can see this in the Figure particles of the cooler substance. Thermal energy is transferred in this way until both substances have the same thermal energy and temperature. Q: How is thermal energy transferred in an oven? A: Thermal energy of the hot oven is transferred to the cooler food, raising its temperature. | text | null |
L_0915 | heat | T_4495 | How do you cool down a glass of room-temperature cola? You probably add ice cubes to it, as in the Figure 1.2. You might think that the ice cools down the cola, but in fact, it works the other way around. The warm cola heats up the ice. Thermal energy from the warm cola is transferred to the much colder ice, causing it to melt. The cola loses thermal energy in the process, so its temperature falls. | text | null |
L_0915 | heat | T_4495 | How do you cool down a glass of room-temperature cola? You probably add ice cubes to it, as in the Figure 1.2. You might think that the ice cools down the cola, but in fact, it works the other way around. The warm cola heats up the ice. Thermal energy from the warm cola is transferred to the much colder ice, causing it to melt. The cola loses thermal energy in the process, so its temperature falls. | text | null |
L_0916 | heat conduction | T_4496 | Conduction is the transfer of thermal energy between particles of matter that are touching. Thermal energy is the total kinetic energy of moving particles of matter, and the transfer of thermal energy is called heat. Conduction is one of three ways that thermal energy can be transferred (the other ways are convection and thermal radiation). Thermal energy is always transferred from matter with a higher temperature to matter with a lower temperature. | text | null |
L_0916 | heat conduction | T_4497 | To understand how conduction works, you need to think about the tiny particles that make up matter. The particles of all matter are in constant random motion, but the particles of warmer matter have more energy and move more quickly than the particles of cooler matter. When particles of warmer matter collide with particles of cooler matter, they transfer some of their thermal energy to the cooler particles. From particle to particle, like dominoes falling, thermal energy moves through matter. In the opening photo above, conduction occurs between particles of metal in the cookie sheet and anything cooler that comes into contact with ithopefully, not someones bare hands! | text | null |
L_0916 | heat conduction | T_4498 | The cookie sheet in the opening image transfers thermal energy to the cookies and helps them bake. There are many other common examples of conduction. The Figure 1.1 shows a few situations in which thermal energy is transferred in this way. Q: How is thermal energy transferred in each of the situations pictured in the Figure 1.1? A: Thermal energy is transferred by conduction from the hot iron to the shirt, from the hot cup to the hand holding it, from the flame of the camp stove to the bottom of the pot as well as from the bottom of the pot to the food inside, and from the feet to the snow. The shirt, hand, pot, food, and snow become warmer because of the transferred energy. Because the feet lose thermal energy, they feel colder. | text | null |
L_0917 | heating systems | T_4499 | Modern home heating systems keep us comfortable in cold weather. We may even depend on them for our survival. But we often take them for granted. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. Thermal energy is the total energy of moving particles of matter. The transfer of thermal energy is called heat. Therefore, a heating system is a system for the transfer of thermal energy. Regardless of the type of heating system in a home, the basic function is the same: to produce thermal energy and transfer it to air throughout the house. | text | null |
L_0917 | heating systems | T_4500 | A hot-water heating system produces thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a simple diagram of this type of heating system in the Figure 1.1. Water is heated in a boiler that burns a fuel such as natural gas or heating oil. The boiler converts the chemical energy stored in the fuel to thermal energy. The heated water is pumped from the boiler through pipes and radiators throughout the house. There is usually a radiator in each room. The radiators get warm when the hot water flows through them. The warm radiators radiate thermal energy to the air around them. The warm air then circulates throughout the rooms in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. Q: Look closely at the hot-water heating system in the Figure 1.1. The radiator is a coiled pipe through which hot water flows. What happens to the water as it flows through the radiator? Why is each radiator connected to two pipes? Why cant water flow directly from one radiator to another through a single pipe? A: The radiator is where most of the energy transfer occurs. Water passes through such a great length of pipe in the radiator that it transfers a lot of thermal energy to the radiator. As the water transfers thermal energy, it gets cooler. The cool water flows into a return pipe rather than going directly to another radiator because the cool water no longer has enough thermal energy to heat a room. | text | null |
L_0917 | heating systems | T_4501 | A warm-air heating system uses thermal energy to heat air and then forces the warm air through a system of ducts and registers. You can see a this type of heating system in the Figure 1.2. The air is heated in a furnace that burns fuel such as natural gas, propane, or heating oil. After the air gets warm, a fan blows it through the ducts and out through the registers that are located in each room. Warm air blowing out of a register moves across the room, pushing cold air out of the way. The cold air enters a return register across the room and returns to the furnace with the help of another fan. In the furnace, the cold air is heated, and the cycle repeats. Q: How does a home heating system know when to run and when to stop running? A: A home heating system is turned on or off by a thermostat. | text | null |
L_0917 | heating systems | T_4502 | A thermostat, like the one seen in the Figure 1.3, is an important part of any home heating system. It is like the brain of the entire system. It constantly monitors the temperature in the home and tells the boiler or furnace when to turn on or off. The thermostat is set at a selected temperature, say 71 F. When the temperature in the home starts to fall below this point, the thermostat triggers the boiler or furnace to start running. When the temperature starts to rise above this point, the thermostat triggers the boiler or furnace to stop running. In this way, the thermostat maintains the homes temperature at the set point. | text | null |
L_0917 | heating systems | T_4502 | A thermostat, like the one seen in the Figure 1.3, is an important part of any home heating system. It is like the brain of the entire system. It constantly monitors the temperature in the home and tells the boiler or furnace when to turn on or off. The thermostat is set at a selected temperature, say 71 F. When the temperature in the home starts to fall below this point, the thermostat triggers the boiler or furnace to start running. When the temperature starts to rise above this point, the thermostat triggers the boiler or furnace to stop running. In this way, the thermostat maintains the homes temperature at the set point. | text | null |
L_0919 | hydrocarbons | T_4508 | Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons are the simplest type of carbon-based compounds, but they can vary greatly in size. The smallest hydrocarbons have just one or two carbon atoms. The largest hydrocarbons may have thousands of carbon atoms. Q: How are hydrocarbons involved in each of the photos pictured above? A: The main ingredient of mothballs is the hydrocarbon naphthalene. The main ingredient in nail polish remover is the hydrocarbon acetone. The lawn mower runs on a mixture of hydrocarbons called gasoline, and the camp stove burns a hydrocarbon fuel named isobutane. | text | null |
L_0919 | hydrocarbons | T_4509 | The size of hydrocarbon molecules influences their properties, including their melting and boiling points. As a result, some hydrocarbons are gases at room temperature, while others are liquids or solids. Hydrocarbons are generally nonpolar, which means that their molecules do not have oppositely charged sides. Therefore, they do not dissolve in water, which is a polar compound. In fact, hydrocarbons tend to repel water. Thats why they are used in floor wax and similar products. | text | null |
L_0919 | hydrocarbons | T_4510 | Hydrocarbons are placed in two different classes: saturated hydrocarbons and unsaturated hydrocarbons. This classification is based on the number of bonds between carbon atoms. Saturated hydrocarbons have only single bonds between carbon atoms, so the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, they are saturated with hydrogen atoms. Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, so the carbon atoms are not bonded to as many hydrogen atoms as possible. In other words, they are unsaturated with hydrogen atoms. | text | null |
L_0919 | hydrocarbons | T_4511 | It is hard to overstate the importance of hydrocarbons to modern life. Hydrocarbons have even been called the driving force of western civilization. You saw some ways they are used in the opening image. Several other ways are pictured in the Figure 1.1. The most important use of hydrocarbons is for fuel. Gasoline, natural gas, fuel oil, diesel fuel, jet fuel, coal, kerosene, and propane are just some of the commonly used hydrocarbon fuels. Hydrocarbons are also used to make things, including plastics and synthetic fabrics such as polyester. Motor oil: Motor oil consists of several hydrocarbons. It lubricates the moving parts of car engines. Asphalt: Asphalt pavement on highways is made of hy- drocarbons found in petroleum. Candle: Many candles are made of paraffin wax, a solid mixture of hydrocarbons. Lighter: This lighter burns the hydrocarbon named butane. Rain Boots: These rain boots are made of a mixture of several hydro- carbons. Transportation: These forms of transportation are fueled by different mixtures of hydrocarbons. | text | null |
L_0919 | hydrocarbons | T_4512 | The main source of hydrocarbons is fossil fuelscoal, petroleum, and natural gas. Fossil fuels formed over hundreds of millions of years, as dead organisms were covered with sediments and put under great pressure. Giant ferns in ancient swamps turned into coal deposits. The Figure 1.2 shows one way that coal deposits are mined. Dead organisms in ancient seas gradually formed deposits of petroleum and natural gas. Open-Pit Coal Mine | text | null |
L_0920 | hydrogen and alkali metals | T_4513 | Sodium (Na) is an element in group 1 of the periodic table of the elements. This group (column) of the table is shown in Figure below. It includes the nonmetal hydrogen (H) and six metals that are called alkali metals. Elements in the same group of the periodic table have the same number of valence electrons. These are the electrons in their outer energy level that can be involved in chemical reactions. Valence electrons determine many of the properties of an element, so elements in the same group have similar properties. All the elements in group 1 have just one valence electron. This makes them very reactive. Q: Why does having just one valence electron make group 1 elements very reactive? A: With just one valence electron, group 1 elements are eager to lose that electron. Doing so allows them to achieve a full outer energy level and maximum stability. | text | null |
L_0920 | hydrogen and alkali metals | T_4514 | Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the most reactive of all elements. The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very eager to gain an electron. Click image to the left or use the URL below. URL: | text | null |
L_0920 | hydrogen and alkali metals | T_4515 | Besides being very reactive, alkali metals share a number of other properties. Alkali metals are all solids at room temperature. Alkali metals are low in density, and some of them float on water. Alkali metals are relatively soft. Some are even soft enough to cut with a knife, like the sodium pictured in the Figure 1.1. | text | null |
L_0920 | hydrogen and alkali metals | T_4516 | Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. | text | null |
L_0920 | hydrogen and alkali metals | T_4516 | Although all group 1 elements share certain properties, such as being very reactive, they are not alike in every way. Three different group 1 elements are described in more detail below. Notice the ways in which they differ from one another. Q: Why do you think hydrogen gas usually exists as diatomic molecules? A: Each hydrogen atom has just one electron. When two hydrogen atoms bond together, they share a pair of electrons. The shared electrons fill their only energy level, giving them the most stable arrangement of electrons. Potassium is a soft, silvery metal that ignites explosively in water. It easily loses its one valence electron to form positive potassium ions (K+ ), which are needed by all living cells. Potassium is so impor- tant for plants that it is found in almost all fertilizers, like the one shown here. Potassium is abundant in Earths crust in minerals such as feldspar. Francium has one of the largest, heaviest atoms of all elements. Its one valence electron is far removed from the nucleus, as you can see in the atomic model on the right, so it is easily removed from the atom. Francium is radioactive and quickly decays to form other elements such as radium. This is why francium is extremely rare in nature. Less than an ounce of francium is present on Earth at any given time. Q: Francium decays too quickly to form compounds with other elements. Which elements to you think it would bond with if it could? A: With one valence electron, francium would bond with a halogen element in group 17, which has seven valence electrons and needs one more to fill its outer energy level. Elements in group 17 include fluorine and chlorine. | text | null |
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