The structure of the atom is a fundamental concept in physics and chemistry. According to the currently accepted model known as the "electron cloud model" or the "quantum mechanical model," atoms are composed of three main subatomic particles: protons, neutrons, and electrons. 

- **Protons:** Protons are positively charged particles found in the nucleus of an atom. They have a relative mass of 1 atomic mass unit (amu) and carry a charge of +1.

- **Neutrons:** Neutrons are neutral particles also located in the nucleus of an atom. They have a mass similar to protons (approximately 1 amu) but carry no electric charge.

- **Electrons:** Electrons are negatively charged particles that orbit around the nucleus in specific energy levels or shells. They have a negligible mass compared to protons and neutrons. Electrons exist in regions of space known as orbitals or electron clouds, and their behavior is described by quantum mechanics.

The number of protons determines the atomic number of an element, while the sum of protons and neutrons gives the atomic mass number. Atoms of different elements have different numbers of protons. For example, hydrogen atoms have one proton, carbon atoms have six protons, and so on.

The electrons are distributed in different energy levels or shells around the nucleus. The innermost shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and subsequent shells can accommodate even more. The electrons in the outermost shell, called the valence shell, are responsible for an atom's chemical properties.

The arrangement and interactions of these subatomic particles determine the characteristics and behavior of atoms, including their chemical reactivity, bonding, and physical properties. The study of atomic structure and the behavior of atoms is crucial in understanding various scientific fields, such as chemistry, physics, and materials science.
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