Question

Question 3.28 The increasing order of reactivity among group 1 elements is Li < Na < K < Rb CI > Br > I. Explain.

Class XI Classification of Elements and Periodicity in Properties Page 94

Answer 1

full 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 :- chemical reactivity of alkali metals { group 1 } is exhibited by the loss of electron leading to the formation of cation . but tendency to loss electron in group is increases when we move down the group. and hence , reactivity increases down the group .
e.g., order of reactivity is Li < Na < K < Rb < Cs

but in case of halogens { group 17 } , chemical reactivity is exhibited by the gain of electron leading to the formation of anion . we know, tendency of gain electron in group decreases down the group . and hence, reactivity decreases down the group .
e.g., order of reactivity is F > Cl > Br > I

Answer 2

Answer:

In group 1 elements as we go down the size increases and the attraction of nucleus on valence electrons gets weaker.So they can be lost easily to form cations.Cs is most downward situated in group 1 so it has most favorable conditions to lose electrons thereby forming cation and reacting with some other element.

And in group 17 the size of F is smallest and it can't easily accomodate coming electron or electrons due to electron-electron replusion between the coming ones and already present ones.So as we move down the group this problem decreases due to increase in size of atoms.So they can accept easily the coming electron or electrons.That's why reactivity of I is greater than the rest mentioned in ques (in group 17).

Explanation: