Question

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

Answer 1

Variation in valency

On moving from left to right in the periodic table, valency increases up to 4 and then decreases.

• The electrons present in the last shell determine the valency of a particular element.
• If the number of valence electrons is less than or equal to 4, valency = number of valence electrons
• If the number of valence electrons is more than 4, valency = 8 - number of valence electrons

Variation in atomic size:-

Atomic size decreases along a period. This is because on moving across a period, the number of valence shells remains the same and the electrons increase by one unit. As a result, the nuclear charge increases and thus, the atomic radius decreases.