With reference to the alkali metals in Group 1 [IA] and the halogens i

1.	With reference to the alkali metals in Group 1 [IA] and the halogens in 17 [VIIA] explain the trend in ionisation potential, electron affinity and electronegativity on moving down the groups in the periodic table.
Answer» (1) Trends in periodic properties (Group 1) Group 1 elements are Li (At. no. = 3), Na (At. no. = 11), K(At. no. = 19), Rb(At. no. = 37), Cs (At. no. = 55). (a) Trend in ionisation potential: On moving down the group, ionisation potential decreases, i. e., ionisation potential decreases in the order: Li > Na > K > Rb > Cs. Reason: On moving down the group, atomic size, as well as, nuclear charge increases. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group. (b) Trend in electron affinity: On moving down the group, electron affinity decreases, e., electron affinity decreases in the order: Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential. (c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order : Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential. (2) Trends in periodic properties (Group 17): Group 17 elements are F (At. no. = 9), Cl (At. no. = 17), Br (At. no. = 35) and I (At. no. = 53). (a) Trend in Ionisation potential: On moving down the group ionisation potential decreases, e. ionisation potential decreases in the order : F > Cl > Br > I. Reason: On moving down the group, atomic size number of shells as well as nuclear charge increase. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group. (b) Trend in electron affinity: On moving down the group, electron affinity, in general, decreases. However, the actual order of change in electron affinity is : F < Cl > Br > I. Reason : Same as in case of ionisation potential. (c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order: F > Cl > Br > I. Reason: Same as in case of ionisation potential.

With reference to the alkali metals in Group 1 [IA] and the halogens in 17 [VIIA] explain the trend in ionisation potential, electron affinity and electronegativity on moving down the groups in the periodic table.

Answer»

(1) Trends in periodic properties (Group 1)

Group 1 elements are Li (At. no. = 3), Na (At. no. = 11), K(At. no. = 19), Rb(At. no. = 37), Cs (At. no. = 55).

(a) Trend in ionisation potential: On moving down the group, ionisation potential decreases, i. e., ionisation potential decreases in the order: Li > Na > K > Rb > Cs.

Reason: On moving down the group, atomic size, as well as, nuclear charge increases. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group.

(b) Trend in electron affinity: On moving down the group, electron affinity decreases, e., electron affinity decreases in the order: Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential.

(c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order : Li > Na > K > Rb > Cs. Reason: Same as that in ionisation potential.

(2) Trends in periodic properties (Group 17): Group 17 elements are F (At. no. = 9), Cl (At. no. = 17), Br (At. no. = 35) and I (At. no. = 53).

(a) Trend in Ionisation potential: On moving down the group ionisation potential decreases, e. ionisation potential decreases in the order : F > Cl > Br > I.

Reason: On moving down the group, atomic size number of shells as well as nuclear charge increase. However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. As such ionisation potential decreases down the group.

(b) Trend in electron affinity: On moving down the group, electron affinity, in general, decreases. However, the actual order of change in electron affinity is : F < Cl > Br > I.

Reason : Same as in case of ionisation potential.

(c) Trend in electronegativity: On moving down the group, electronegativity decreases, e., electronegativity decreases in the order: F > Cl > Br > I.

Reason: Same as in case of ionisation potential.

With reference to the alkali metals in Group 1 [IA] and the halogens in 17 [VIIA] explain the trend in ionisation potential, electron affinity and electronegativity on moving down the groups in the periodic table.

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