Why with travelling from left to right in a period atomic size decreases but suddenly increases in group 18

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Solution

Along the period, atomic size decreases due to an increase in effective nuclear charge.

This means that though the number of protons keeps increasing in the nucleus, the electrons are added to the same shell. This way the nucleus is able to keep a tight hold on the electrons (attraction is high) and thus the size is small.

Keep in mind, this doesn't apply to Group 18 elements since they are stable and have completely filled shells. They have Van Der Waals radii, which is bigger than covalent or ionic radii that all the other group members have.

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Similar questions

Give scientific reasons:

1. Atomic size increases down the group.

2. Metallic character decreases from left to right in a period.

3. Elements in the same group show same valency.

2^{n d}

As we know that if size of atomic radii increases, I.E decreases. But why it is said in a random topic that I.E increases down the group?

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