Question

In modern periodic table , while moving from left to right in a period, the size of atom of each consecutive element decreases, except noble gas atom. Explain why?

Answer 1

HELLO THERE!!

Fantastic question, a tricky one....

Here's your answer:

When we move from left to right across a period, the number of valence electrons increase by one but the number of shells remain the same.

Hence, the nuclear pull on the valence electrons increases due to which the atomic radius decreases, and the size, hence, decreases.


Now, this is not in case of noble gases.

Noble gases have a complete outer shell configuration (duplet in Helium and octet in other gases). Hence, there is a great repulsive force between the electrons in the outermost shell, due to which, there is a wobbling up of the atom.

Hence, an atom of noble gases are generally large.



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