24. Define modern periodic law.
25. What are isoelectronic ions? Give examples.
26. What is effective nuclear charge ?
27. Is the definition given below for ionisation enthalpy is correct?
"Ionisation enthalpy is defined as the energy required to remove the most loosely bound electron from the valence shell of an atom"
28. Magnesium loses electrons successively to form Mg+, Mg2+ and Mg3+ ions. Which step will have the highest ionisation energy and why?
29. Define electronegativity.
30. How would you explain the fact that the second ionisation potential is always higher than first ionisation potential?
31. Energy of an electron in the ground state of the hydrogen atom is -2.8 x 10-18 J. Calculate the ionisation enthalpy of atomic hydrogen in terms of kJ mol-1.
32. The electronic configuration of atom is one of the important factor which affects the value of ionisation potential and electron gain enthalpy. Explain
33. In what period and group will an element with Z = 118 will be present?
34. Justify that the fifth period of the periodic table should have 18 elements on the basis of quantum numbers.
35. Elements a, b, c and d have the following electronic configurations:
a: 1s2, 2s2, 2p6
b: 1s2, 2s2, 2p6, 3s2, 3p1
c: 1s2, 2s2, 2p6, 3s2, 3p6
d: 1s2, 2s2, 2p1
36. Give the general electronic configuration of lanthanides and actinides?
37. Why halogens act as oxidising agents?
38. Mention any two anomalous properties of second period elements.
39. Explain the pauling method for the determination of ionic radius.
40. Explain the periodic trend of ionisation potential.
41. Explain the diagonal relationship.
42. Why the first ionisation enthalpy of sodium is lower that that of magnesium while its second ionisation enthalpy is higher than that of magnesium?
43. By using paulings method calculate the ionic radii of K+ and Cl- ions in the potassium chloride crystal. Given that dK+-Cl- = 3.14 A
44. Explain the following, give appropriate reasons.
i. Ionisation potential of N is greater than that of O
ii. First ionisation potential of C-atom is greater than that of B atom, where as the reverse is true is for second ionisation potential.
iii. The electron affinity values of Be, Mg and noble gases are zero and those of N (0.02 eV) and P (0.80 eV) are very low
iv. The formation of F- (g) from F(g) is exothermic while that of O2-(g) from O (g) is endothermic.
45. What is screening effect? Briefly give the basis for pauling's scale of electronegativity.
46. State the trends in the variation of electronegativity in group and periods.