Observe the following table
Element name sodium aluminium potassium
Atom no 11 13 19

Based on the above information what can you say about the size of an atom

Based on the electronic configuration choose the atom that forms am ion.Give reason

1s1 2s2 2p6
1s2 2s2 2p6 3s1



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As you go further from 11,12,13 ,14 ...................etc.the charge density goes on increaing which means the attraction ofelectrons with the nucleus increasesand hence size shrinks or decreases 

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AS one moves across in the period, the size of atom decreases. This is because of increase in the number of protons and increased attraction on the electrons in the valency shell.

As one moves down a group, the size increases, as there is a new shell in the next period in the same group,

So sodium  to aluminum  are in the same  period.  -- 2.
Then potassium is in the next period  -- 3.