Question

the increasing order of reactivity among group 1 elements is Li<Na<K<Rb<C's whereas that among the group 17 elements is F>Cl>Br>I. Explain​

Answer 1

Solution :-

$\bigstar \: \mathtt{ Li < Na < K < Rb < Cs }$

• In case of group 1 elements , reactivity  usually depends on the factor of ionization energy .
• Ionization energy is the energy required to remove an electron from the outer most shell .

• Ionization energy increases across a period and decreases down the group

Hence ,  down the group reactivity increases

$\bigstar \: \mathtt{ F > Cl > Br > I }$

• In case of Grp 17 elements ,  reactivity usually depends on the factor of electronegativity

• Electronegativity is the tendency of an element to accept electrons

• Electronegativity increases across a period and decreases down the group

Hence , the reactivity decreases down the group

Answer 2

$\sf\huge\underline\green{Solution:-}$

→ In group 1 elements (alkali metals) the reactivity of the metals is mainly due to the electron releasing tendency of their atoms, which is related to ionisation enthalpy. As we know, the ionisation enthalpy decreases down the group, the reactivity of alkali metals increases

→ 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. As we know, both of these decrease down the group, the reactivity therefore decreases.

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