# Out of Sr, Ca, As, N, which element has the smallest atomic radius?

Nov 7, 2016

The answer is $N$. Why?

#### Explanation:

Got a Periodic Table? Of course you have, because you are doing your Chemistry homework, and a Periodic Table will be at hand! Anyway, ATOMIC radii DECREASE across a Period (i.e. a row as we look at the Table from LEFT to RIGHT), and INCREASE down a Group, a column of the Table.

We have Period 5 $S r$, and Period 4 $C a$, both metals to the left hand side of the Table, and Period 4 $A s$. Arsenic is without doubt the smallest of these atoms. But arsenic is without doubt LARGER than nitrogen, which is a 2nd Period atom to the right of the Periodic Table.

If I included oxygen, fluorine, and neon, could you make a prediction with respect to atomic size? The answer should be fairly clear.