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## CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES

(A) GENESIS OF PERIODIC CLASSIFICATION 1. Why has Group 0 been placed at the extreme right of the periodic table? 2. What was the basis of classifying the elements by Lothar Meyer? 3. State any two significant features of the Mendeleevs periodic table. 4. Which important property did Mendeleev use to classify the elements in his periodic table and did hi stick to that? (NCERT) 5. What was the basis of classifying elements in Mendeleevs periodic table? What were the three main drawbacks of this periodic table? 6. Comment on the need to classify elements. Explain the earliest attempts at classifying elements by Dobereiner and Newlands. 7. Why were the names ekaaluminium and ekasilicon given to gallium and germanium by Mendeleev? 8. State any three defects in the Mendeleevs periodic table. 9. State Newlands law of octaves. 10. State Mendeleevs periodic law. 11. What were the elements that filled the gaps ekaaluminium and ekasilicon? 12. Name some of the earliest attempts to classify elements. What was their basis of classification? 13. What are the limitations of Mendeleevs periodic table? 14. Write a short note on the predictions made by Mendeleev that led to the discovery of new elements. 15. What was the original and modified form of Mendeleevs periodic table? 16. What were the advantages and limitations of Mendeleevs periodic table? 17. Write a note on the genesis of periodic classification citing each method adopted till the formulation of the modern periodic table. (B) MODERN PERIODIC LAW AND THE PRESENT FORM OF THE PERIODIC TABLE 18. What is the basis of classifying the elements in the modern periodic table? 19. Can an element with atomic number 126, if discovered, be accommodated in the present set up of the long form of the periodic table? 20. What is the basic theme of organization in the periodic table? (NCERT) 21. Why do elements in the same group have similar physical and chemical properties? (NCERT) 22. In the modern periodic table, the period indicates the value of : (NCERT) (a) atomic number (b) atomic mass (c) principal quantum number (d) azimuthal quantum number 23. Which of the following statements related to the modern periodic table is incorrect? (a) The p-block has 6 columns, because a maximum of 6 electrons can occupy all the orbitals in a p-shell.

## 24. 25. 26.

27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37.

(b) The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitals in a dsubshell. (c) Each block contains a number of columns equal to the number of electrons that can occupy that subshell. (d) The block indicates value of azimuthal quantum number (l) for the last subshell that received electrons in building up the electronic configuration. (NCERT) State the modern periodic law and explain how it differs from Mendeleevs periodic law. What is the number of groups and periods in the modern periodic table? What is the number of elements in each period? Describe some of the evidence that could be used to justify the argument that the modern periodic table is based on similarities in the chemical properties of the elements. Give evidence that could be used to justify the argument that the modern periodic table groups elements with similar electronic configurations. Lanthanoids and actinoids are placed in separate rows at the bottom of the periodic table. Explain the reason for this arrangement. Where are the elements with similar physical and chemical properties placed in the periodic table? Which properties of the elements depend on the electronic configuration of the atoms and which do not? What are horizontal rows and vertical columns of the periodic table called? What are the atomic numbers of elements which constitute f-block (lanthanoids and actinoids)? Helium has an electronic configuration of 1s2 but it is placed in i-block in Group 18. Explain. What is the long form of periodic table also known as? What are the advantages and disadvantages of the present form of periodic table? On what basis did Mosley classify elements? Describe the main features of the long form of the periodic table. In what respects is it superior to Mendeleevs table? Justify the given statement with suitable examples the properties of the elements are a periodic function of their atomic numbers.

(C) NOMENCLATURE OF ELEMENTS WITH ATOMIC NUMBERS > 100 38. What would be IUPAC names and symbols for elements with atomic numbers 122, 127, 135, 149 and 150? 39. The element 118 has not been discovered. What could be IUPAC name and symbol for this element? On the basis of the periodic table, predict the electronic configuration of this element and also the formula of its most stable chloride and oxide. 40. In terms of period and group where would you locate the element with Z = 114? (NCERT) 41. Which element do you think would have been named by (a) Lawrence Berkeley Laboratory (b) Seaborgs group? (NCERT) 42. What would be the IUPAC name and symbol for the element with atomic number 118? 43. Discuss the rules for naming elements with atomic numbers greater than 100.

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The element with atomic number 119 has not been discovered so far. Predict its IUPAC name and symbol. Based on periodic table, predict the electronic configuration of the element and the formula of its most stable chloride and oxide. ELECTRONIC CONFIGURATIONS OF ELEMENTS AND THE PERIODIC TABLE AND ELECTRONIC CONFIGURATIONS AND TYPES OF ELEMENTS: s-, p-, d-, f- BLOCKS How many elements are present in the third period of the p- block elements? All transition elements are d- block elements, but all d- block elements are not transition elements. Explain. Why are the Group 1 elements called alkali metals and Group 17 elements called halogens? Which family of elements has the electronic configuration ns2 np2? Write the atomic number of the element present in the third period and Group 17 of the periodic table. (NCERT) On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements. (NCERT) Use the periodic table to answer the following questions. (a) Identify an element with five electrons in the outer subshell. (b) Identify an element that would tend to lose two electrons. (c) Identify an element that would tend to gain two electrons. (d) Identify the group having metal, non-metal, liquid as well as gas at the room temperature.(NCERT) Write the general outer electronic configuration of s-, p-, d- and f- block elements. (NCERT) Assign the position of the element having outer electronic configuration (i) ns2 np4 for n = 3 (ii) (n - 1)d2 ns2 for n = 4, and (iii) (n-2)f7 (n - 1)d1 ns2 for n = 6, in the periodic table. (NCERT) Which elements have the following electron configurations? (Use only the periodic table) (a) 1s2 2s2 2p5 (b) [Ar] 4s2 3d10 4p1 (c) [Xe] 6s2 2 1 7 1 10 (d) [Xe] 6s 5d 4f (e) [Ar] 4s 3d (exception to rules) Write the number designation of a group that has 2 electrons beyond a noble gas configuration. Write the number designation of a group with 12 electrons beyond a noble gas configuration. Write the electronic configurations for the elements of atomic numbers 6, 11, 17 and 25 and from this decide to which group in the periodic table each element belongs. Write the name and symbol for each of these. Give the name and symbol for each of the atoms which have the ground state electronic configurations in their outer shells: (a) 2s2 (b) 3s2 3p5 (c) 3s2 3p6 4s2 2 6 6 2 2 2 (d) 3s 3p 3d 4s (e) 5s 5p and (f) 5s2 5p6 What is the general outer electronic configuration of s-, p-, d- and f- block elements? Comment on their metallic character, nature of compounds formed and nature of oxides.

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(a) Write the electronic configurations of the elements: A (atomic number = 9), B (atomic number = 12), C (atomic number = 29), D (atomic number = 54) and E (atomic number = 58). (b) Also predict the period, group number and block to which they belong. (c) Classify them as representative elements, noble gases, transition and inner transition elements. Predict the position of the element in the periodic table satisfying the electronic configuration (n 1)d1 ns2 for n = 4. Elements A, B, C, D and E have the following electronic configurations: A: 1s2 2s2 2p6 3s2 3p1 B: 1s2 2s2 2p5 C: 1s2 2s2 2p6 3s2 3p6 3d5 4s1 D: 1s2 2s2 2p6 3s2 3p5 3d10 4s2 4p6 4d5 5s1 2 2 6 2 6 2 E: 1s 2s 2p 3s 3p 4s Which among these will belong to the same in the periodic table? Elements A, B, C, D and E have the following electronic configurations: A: 1s2 2s2 2p1 B: 1s2 2s2 2p6 3s2 3p1 C: 1s2 2s2 2p6 3s2 3p3 D: 1s2 2s2 2p6 3s2 3p5 E: 1s2 2s2 2p6 3s2 3p6 4s2 4p3 Which among these will belong to the same in the periodic table? Predict the position of the element in the periodic table satisfying the electron configuration (n-1) d5 ns1 for n = 4. Explain in terms of electronic configuration why the halogens have similar chemical properties. Name the block to which the elements having the following outer electronic configurations belong to: (a) 2s2 2p4 (b) 6s2 4f3 (c) 3d10 4s2 and (d) 2s2 2p6 3s2? Give some characteristics of d-block elements. On the basis of electronic configurations, justify that the second and third periods contains 8 elements each, fourth and fifth periods contain 18 elements each and the sixth period contains 32 elements. Name the four blocks into which the elements of the periodic table have been classified. Why are they named so? List groups of periodic table belonging to each block. Which elements are called inner transition elements? Name the different inner transition series. Why are they so named? (a) Elements A, B, C and D have atomic numbers 12, 19, 29 and 36, respectively. Based on their electronic configurations, predict the group to which these belong to. (b) Predict the blocks and the periods to which they belong. (c) Which of these are representative elements? (a) The electronic configuration of the elements is a periodic property. Justify the statement. (b) What are the exceptions to the normal order of filling? Give examples. Classify the elements having atomic numbers as given below into three separate pairs on the basis of similar chemical properties. Give brief electronic explanation: 9, 12, 16, 34, 53, 56. Give the name and atomic number of the inert gas atom in which the total number of d- electrons is equal to the difference in numbers of total p and s- electrons. Would you regard Zn, Cd and Hg as s- or d- block elements? Give reasons for your answer.

(F) PERIODIC TRENDS IN PHYSICAL PROPERTIES (G) PERIODIC TRENDS IN CHEMICAL PROPERTIES and

## (H) 75. 76. 77. 78. 79. 80. 81. 82.

PERIODIC TRENDS AND CHEMICAL REACTIVITY How do the metallic and non-metallic characters vary on moving from left to right in a period? The radius of Na+ ion is less than that of Na atom. Give reason. Among alkali metals, which element do you except to be most electronegative and why? The first and second ionization potentials of helium atoms are 24.58 eV and 54.4 eV, respectively. Calculate the energy in kJ required to produce 1 mol of He2+ ions. The electron gain enthalpy of bromine is 3.36eV. How much energy in kcal is released when 8 g of bromine is completely converted to Br ions in the gaseous state? (1 eV = 23.06 kcal mol-1). Predict the formulas of the stable binary compounds that would be formed by the following pairs of elements: (a) calcium and oxygen (b) aluminium and carbon. What do atomic radius and ionic radius really mean to you? (NCERT) How do atomic radius vary in a period and in a group? How do you explain the variation? (NCERT) What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions. (a) F , (b) Ar, (c) Mg2+, (d) Rb+. (NCERT) Consider the following species: N3, O2, F , Na+, Mg2+ and Al3+ (a) What is common in them? (b) Arrange them in the order of increasing ionic radii. (NCERT) What is the significance of the terms isolated gaseous atom and ground state while defining the ionization enthalpy and electron gain enthalpy? (NCERT) Energy of an electron in the ground state of the hydrogen atom is -2.18 10-18 J. Calculate the ionization enthalpy of atomic hydrogen in terms of J mol-1. (NCERT) Among the second period elements the actual ionization enthalpies are in the order Li < B < Be < C < O < N < F < Ne. Explain why (a) Be has higher ionization enthalpy than B (b) O has lower ionization enthalpy than N and F? How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium? (NCERT) What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group? (NCERT) The first ionization enthalpy values (in kJ mol-1) of Group 13 elements are: B 801 Al 577 Ga 579 In 558 Tl 589

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How would you explain this deviation from the general trend ? (NCERT) Which of the following pairs of elements would have a more negative electron gain enthalpy: (a) O or F (b) F or Cl? (NCERT) Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer. (NCERT) What is the basic difference between the terms electron gain enthalpy and electronegativity? (NCERT) How would you react to the statement that the electronegativity of N on Pauling scale is 3.0 in all the nitrogen compounds? (NCERT) Describe the theory associated with the radius of an atom as it (a) gains an electron (b) loses an electron. (NCERT) Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer. (NCERT) What are the major differences between metals and non-metals? (NCERT) The increasing order of reactivity among group 1 elements is Li < Na < K < Rb < Cs whereas that among Group 17 elements is F > CI > Br > I. Explain. (NCERT) The first (iH1) and the second (iH2) ionization enthalpies (in kJ mol-1) and the (egH) electron gain enthalpy (in kJ mol-1) of a few elements are given below: Elements I II III IV V VI H1 520 419 1681 1008 2372 738 H2 7300 3051 3374 1846 5251 1451 egH -60 -48 -328 -295 +48 -40

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100. Which of the above elements is likely to be: (a) the least reactive element. (b) the most reactive metal. (c) the most reactive non-metal. (d) the least reactive non-metal. (e) the metal which can form a stable binary halide of the formula MX2(X=halogen).

(f) the metal which can form a predominantly stable covalent halide of the formula MX (X = halogen)? (NCERT) Predict the formulas of the stable binary compounds that would be formed by the combination of the following pairs of elements: (a) Lithium and oxygen (b) Magnesium and nitrogen (c) Aluminium and iodine (d) Silicon and oxygen (e) Phosphorus and fluorine (f) Element 71 and fluorine (NCERT) Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell? (a) Valence principal quantum number (n) (b) Nuclear charge (Z ) (c) Nuclear mass (d) Number of core electrons. (NCERT) The size of isoelectronic species F-, Ne and Na+ is affected by (a) nuclear charge (Z ) (b) valence principal quantum number (n) (c) electron-electron interaction in the outer orbitals (d) none of the factors because their size is the same. (NCERT) Which one of the following statements is incorrect in relation to ionization enthalpy? (a) Ionization enthalpy increases for each successive electron. (b) The greatest increase in ionization enthalpy is experienced on removal of electron from core noble gas configuration. (c) End of valence electrons is marked by a big jump in ionization enthalpy. (d) Removal of electron from orbitals bearing lower n value is easier than from orbital having higher n value. (NCERT) Considering the elements B, Al, Mg, and K, the correct order of their metallic character is : (a) B > Al > Mg > K (b) Al > Mg > B > K (c) Mg > Al > K > B (d) K > Mg > Al > B (NCERT) Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is : (a) B > C > Si > N > F (b) Si > C > B > N > F (c) F > N > C > B > Si (d) F > N > C > Si > B (NCERT) Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is : (a) F > Cl > O > N (b) F > O > Cl > N (c) Cl > F > O > N (d) O > F > N > Cl (NCERT)

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108. (a) How does the size of atoms vary from left to right in a period, and on descending a group in the periodic table? What are the reasons for these changes? (b) How can we explain the large atomic radii of the noble gases? 109. Discuss the changes in atomic size when an atom (a) gains an electron and (b) loses an electron. 110. Explain why: (a) The covalent radius of an atom is smaller than the metallic radius of the atom. (b) The decrease in size between Li and Be is much greater than that between Na and Mg or K and Ca? 111. Is the radius of the valence shell of Na greater than, smaller than or the same as the radius of the valence shell of Li? Give reasons. 112. Noble gases form neither anions nor cations. Why? 113. List the factors that can influence the ionic radius of an element. 114. Arrange the elements B, Al, C Si and F in: (a) Increasing order of atomic size. (b) Increasing order of first ionization enthalpy. (c) Increasing order of non-metallic character. 115. Explain what is meant by the ionization enthalpy of an element. Why does it take energy to remove and electron from an isolated atom in the gas phase? 116. (a) Explain why the ionization enthalpy of nitrogen in Group 15 is more than that of oxygen in Group 16. (b) Account for the fact that there is a decrease in first ionization enthalpy from Be to B and Mg to Al. 117. (a) Which electron is harder to remove from an Li atom, the one in the outermost shell or the one in the innermost shell? Explain. (b) If a single electron is removed from Li atom, the resulting Li+ cation has only two electrons, both in the n = 1 shell. In this respect, it is very similar to an He atom. Compare the ionization enthalpy of Li+ with that of He atom? Explain your reasoning. 118. Describe the general trend in first ionization enthalpies from left to right across the second row of the periodic table and from top to bottom of a column of the periodic table. 119. Discuss how the variation in ionization enthalpy can be related to the (a) electronic structure and (b) atomic size of the atoms. 120. Among the elements K, Mg, C and N, which would show the greatest difference in first and second ionization enthalpies? 121. Account for the following: (a) The radius of the cation is less than that of the parent ion, while that of an anion is more. (b) Covalent radii are shorter than the ionic radii. (c) Value of second ionization enthalpy is greater than the first. (d) Noble gases have positive electron gain enthalpy. 122. (a) Explain why the substantial decrease in first ionization enthalpy is observed between Na and K, and Mg and Ca, is not observed between Al and Ga. (b) What is the significance of the large increase in the third ionization enthalpy of Ca and the fifth ionization enthalpy of Si? (c) Which would you expect to be larger, the first ionization enthalpy of Rb or Sr and Cl or Br? Explain why.

123. (a) Why is the first ionization enthalpy of the transition elements reasonably constant? (b) Explain the trend in ionization enthalpies for the noble gases. 124. What is electronegativity and how is it related to the type of bond formed? 125. List the different scales of electronegativity and briefly describe Paulings scale. 126. Justify the following: (a) The ionization enthalpies of two isotopes of an element are the same. (b) The first electron gain enthalpy of oxygen is negative, while the second electron gain enthalpy is positive. (c) Chlorine from Cl- more easily than fluorine form F-. (d) The order of reactivity increases down the group in alkali metals (Li < Na < K < Rb < Cs) whereas it decreases down the group in case of halogens (F > Cl > Br > l). 127. Predict the formulas of the stable binary compounds formed between the following pair of elements: (a) Sodium and Oxygen (b) Calcium and Fluorine (c) Nitrogen and Chlorine (d) Lithium and Nitrogen (e) Carbon and Oxygen (f) Aluminium and Bromine 128. What are isoelectronic species? List the factors that affect their size. Arrange the isoelectronic species Na+, F-, Ne, Mg2+, Al3+ in the increasing order of their radii. 129. The electron gain enthalpy of fluorine is -333 kJ mol-1. Calculate the amount of energy released when 1g of fluorine is converted into fluorine ions in the gaseous state. 130. The ionization enthalpy of sodium is 495 kJ mol-1. Calculate the energy required in joules to convert all atoms of sodium in 2.6g of sodium vapor into sodium ions. 131. The first ionization enthalpy of carbon atom is greater than that of boron, whereas the reverse is true for the second ionization enthalpy. Explain. Arrange the following elements in the increasing order of non-metallic character: B, C, Si, N, F. 132. Arrange the following ions in order of decreasing ionic radii: Li+2, He+, Be3+. 133. Explain why the electron gain enthalpy of fluorine is less negative than that of chlorine. 134. Among the elements B, Al, C and Si, (a) which element has the highest first ionization enthalpy? (b) which element has the most metallic character? Justify your answer in each case. 135. Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionization enthalpy than nitrogen. Explain. 136. First member of each group of representative elements (i.e., s- and p- block elements) shows anomalous behavior. Illustrate with two examples. 137. Arrange the following elements in the increasing order of non-metallic character: C, Si, N, F. 138. Out of Na and Mg, which has a higher second ionization enthalpy and why? 139. Explain the meaning of a positive electron gain enthalpy. 140. State which member of each of the following pairs has the greater electron gain enthalpy. (a) Cl, S (b) O, S (c) Si, P (d) N, C 141. Arrange the following in increasing order of ionic size (N3-, Na+, F-, O2-, Mg2+) 142. What do you understand by periodic properties of elements? Name any three such properties. 143. The valence of representative elements is either equal to the number of the valence electrons or eight minus this number. What is the basis of this rule?

144. Discuss briefly periodic trends is chemical reactivity. 145. Discuss the variations in valence amongst the elements of (a) period and (b) groups of the periodic table. 146. Give reason: Ionic compounds of the halogen contain singly charged X- ion and not doubly charged X2- ion. 147. The amount of energy released when l 1010 atoms of chlorine in vapor state are converted to Clions according to the equation, Cl(g) + e- Cl-(g) is 57.86 10-10 J. Calculate the electron gain enthalpy of chlorine atom in terms of kJ mol-1 and eV per atom. 148. Explain what you understand by covalent radius, van der Waals radius, ionic radius and atomic radius. How do they vary in a period and in a group? 149. Ionization potential and electron gain enthalpy of fluorine are 17.42 and -3.45 eV, respectively. Calculate electronegativity of fluorine on Mulliken and Pauling scale. 150. The ionization enthalpy of Li is 5.39 V. If ionization enthalpy of H is 13.6 eV, then calculate the effective charge acting upon outermost electron of Li. 151. Arrange the following ions in order of their increasing ionic radii: Li+, Mg2+, K+, Al3+. 152. The compound M O H can act both as an acid or a base depending upon the ionization enthalpy of the element M. Justify by taking elements (M) of the third period of the periodic table. 153. Arrange the following in decreasing order of their van der Waals radii: Cl, H, O, N. 154. Arrange the elements of second period in order of their increasing second ionization enthalpies.
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