Question

What is the order of the atoms `Fe, P, O` in increasing side?

Answer 1

Do you ask, `"what's the order of increasing size for Fe, P, O"??`

Explanation:

Atomic size decreases across a Period, and increases down a Group. Fourth Period iron should be larger than third Period phosphorus, which should be larger than 2nd Period oxygen.

As chemists, as physical scientists, we should seek out the physical data.

This site reports that the atomic radii of the three elements are: `"Fe, "140xx10^(-12)m; "P, "100xx10^(-12)m;" O, "60xx10^(-12)m.`

Thus `"ATOMIC SIZE"` increases in the order: `"Oxygen, phosphorus, iron"`.

Why should atomic size decrease across a Period?