All the members of group I are metals. Li and Na react with water rapidly whereas K, Rb, and Cs react vigourously. Write the electronic configuration of Li and K and find their valency from the given information. Infer the change in reactivity in a group given atomic numbers of Li and K are 3 and 19 respectively.

All the members of group I are metals. Li and Na react with water rapi

1.	All the members of group I are metals. Li and Na react with water rapidly whereas K, Rb, and Cs react vigourously. Write the electronic configuration of Li and K and find their valency from the given information. Infer the change in reactivity in a group given atomic numbers of Li and K are 3 and 19 respectively.
Answer» Solution :Electronic configuration: `LI (3) to 2, I and K (19) to 2, 8, 8, 1`. VALENCY of both is I since they belong to group one. Since chemical reactivity INCREASES as we move down a group, K, Rb, and Cs which LIE below Li and Na in group I are more reactive.