Question

The increasing order of reactivity among group 1 elements is Li < Na < K < Rb < Cs whereas that among group 17 elements is F > Cl > Br > I. Explain.

Answer 1

"As the enthalpy of ionization decreases in the group from “top to bottom”, the reactivity increases from “Li to Cs”.  

The “group 17 elements” are halogens with an electronic configuration of these elements have ${ ns }^{ 2 }{ np }^{ 6 }$

Following reasons are explain the reactivity nature of all halogens:

Halogens have low dissociation bond energy. It leads to increasing the reactivity nature.

${ F }_{ 2 }$has the low dissociation bond energy.

High electron enthalpy of these elements have a “strong tendency” to “gain an electron” and thus, are “highly reactive”.

${ F }_{ 2 }$has maximum and ${ I }_{ 2 }$ has minimum reduction potentials.

Therefore, order of reactivity is $F\quad >\quad Cl\quad >\quad Br\quad >\quad I$"

Answer 2

Answer:

The increasing order of reactivity among group 1 elements is Li < Na < K < Rb is F > CI > Br > I. ... In group 17 elements (halogens), the reactivity is mainly due to electron gain tendency of the members of the family. Thus reactivity is linked with electronegativity and electron gain enthalpy.