Question

Why Noble Gases are bigger than Halogen but smaller than Alkali metals?​

Answer 1

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✰This is because electrons are added in the same valence shell. Consequently a proton is also increased in the nucleus of the atom. ... In period as we move left to right the atomic radius decreases. So in a period the alkali metal will have the highest Atomic Radius and the Noble gas will have the lowest Atomic Radius.

Answer 2

Required Answer :

→ Noble gases are bigger than Halogens but smaller than Alkali metals. As we move across a period the atomic size goes on decreasing because the nuclear charge increases and the shell number remains the same, thereby bringing the outermost shell closer to the nucleus. Noble gases are placed at the extreme right corner of the periodic table, their size should be smaller than the Halogens but it slightly increases. Because the outermost shell of the noble gases is complete because of which their are maximum number of electronic repulsions and the effect of nuclear pull, i.e. the proton number or nuclear charge over the valence electrons is not seen. So, the atomic size of Noble gases is bigger than the Halogens.

The atomic size of Noble gases is smaller than the Alkali metals because as we move across a period the atomic size goes on decreasing and alkali metals are placed at the extreme left corner of the group and Noble gases are at the extreme right corner.

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About Atomic size ::

Atomic size of an atom is the distance between the centre of its nucleus and the outermost shell.

It depends on two factors :-

1. Number of shells :-

If the number of shells increases then the atomic size increases because the distance between the outermost shell of the atom and nucleus increases. So, the electrons are not attracted with greater force towards the nucleus. Hence, the size increases.

[Atomic size increases across a period and decreases down a group.]

2. Nuclear charge :-

If the nuclear charge increases then the atomic size decrease because the electrons are attracted more towards the nucleus. Thereby, bringing the outermost shell closer to the nucleus which makes the size of atom smaller. And if the nuclear charge decreases then the atomic size increases. As the electrons are not attracted towards the nucleus with greater force. Hence, the size increases.