Question

A) how does valency vary in a group on going from top to bottom? (b) how does atomic size vary in a period on going from left to right?

Answer 1

Valency remains same down the group.

Atomic size decrease as effective nuclear charge increases

Answer 2

if we go down in grp the valence electron in the same group remains same

for Ex. In group valence electron in 1

Therefore valency remains constant in grp

B) on going from left to right in period atomic size decreases becoz while going from left to right the atomic number increases by one that means positive charge on nucleus increase by one unit at time. However the aditional electron vet added to the same outermost shell.Due to the increased nuclear charged the electron are pulled towards the nucleus to a greater and thereby the size of the atom decreases