Question

how do the valency and the atomic size of elements vary while going from left to right along the period of modern periodic table

Answer 1

Atomic Size

Atomic size decreases on going along a period from left to right because the electron enters into the same shell, therefore, attraction between nucleus and outermost electron increases and thus atomic size decreases.

Valency

Valency first increases from 1 to 4 and then decreases from 4 to 0 along a period from left to right. This happens because electron donating power increases and metallic character increases and then electron attracting power increases and non-metallic character increases.

Answer 2

Answer:

valency will be increase & atomic size will decrease because of electro-negativity