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Question

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

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Answer

Below table explains the trends in ionization potential, electron affinity and electronegativity on moving down the groups in the periodic table:

Alkali Metals
Group 1 [IA]		Halogens
Group 17 [VIIA]
Ionization
Potential		On moving down the group both atomic size and nuclear charge increases but atomic size increase dominates over nuclear charge increase hence Ionization Potential decreases down the group.
∴ Li > Na > K > Rb > Cs		Similarly for Halogens too Ionization Potential decreases down the group.
∴ F > Cl > Br > I
Electron AffinityOn moving down the group, electron affinity decreases as atomic size increase dominates over nuclear charge increase hence the atom attracts the electrons with a lesser force.
∴ Li > Na > K > Rb > Cs		Here also electron affinity decreases in general on moving down the group but Fluorine is an exception here as it has lesser electron affinity than Chlorine due to its electronic configuration.
∴ F < Cl > Br > I
ElectronegativitySimilar to electron affinity, electronegativity decreases on moving down the group.
∴ Li > Na > K > Rb > Cs		Electronegativity decreases on moving down the group.
∴ F > Cl > Br > I

💡 Some Related Questions

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With reference to group 1 [IA] of the periodic table – fill in the blanks with the correct word:
The elements are …………… [light/heavy] …………… [metals/non metals] since their atomic size is …………… [large/small]. The energy binding the atoms is …………… [high/low] and hence the elements have …………… [high/low] melting points. The melting points of the elements …………… [increases/decreases] down the subgroup. The electropositive character …………… [increases/decreases] down the subgroup and the elements are strong …………… [reducing/oxidizing] agents. The element with electronic configuration 2, 8, 1 will have …………… [higher/lower] electron affinity and …………… [smaller/larger] atomic size than the element with electronic configuration 2, 1.

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In period 2, element ‘A’ is to the right of element ‘B’
(a) The element ‘A’ would probably have a …………… [smaller/larger] atomic size than ‘B’.
(b) The element ‘B’ would probably have …………… [lower/higher] ionization potential than ‘A’.
(c) The element ‘A’ would have …………… [lesser/higher] electron affinity than ‘B’.
(d) Nuclear charge of element ‘B’ would be …………… [less/more] than element ‘A’.
(e) If an element ‘C’ had a low electronegativity and ionization potential it would have more tendency to …………… [gain/lose] electrons.

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