Question

What is the periodic trend in the variation of valency while going from left to right within a period ? Explain with reference to period 2 & period 3

Answer 1

while going from left to right in a period, the atomic number increases one by one, meaning positive charge on the nucleus increases by one unit at a time. however, the additional electron gets added to the same outermost shell. due to the increased nuclear charge the electrons are pulled towards the nucleus to a greater extent and there by the size of the atom decreases.

Answer 2

On moving from left to right in a period, in the periodic table, the valency first increases and then starts to decrease after a particular point

• Taking the example of Group 2 ( Li, Be, B, C, N, O, F Ne) the valency increases until C, (Li = 1, Be=2, B=3, C=4) after which it starts decreasing ( N =3, O = 2, F = 1, Ne=0).
• Similarly in Group 3 of the periodic table (Na, Mg, Al, Si, P, S, Cl, Ar) the valency increases until Si (Na=1, Mg=2, Al=3, Si=4) after which it starts decreasing (P=3, S=2, Cl=1, Ar=0).

Thus, going from left to right within a period, the valency of the elements increases until a particular point (usually till the element with a valency of 4) after which it starts decreasing.