# How do you find electron configuration using the periodic table?

Jul 12, 2017

Well what is $\text{Z, the atomic number}$ of the element.......?

#### Explanation:

$Z$ gives the number of nuclear protons, and the number of electrons that we have to distribute according to a given scheme......

The scheme is not perfect, and it falls down for chromium metal, which is $Z = 24$, and gives $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{5} 4 {s}^{1}$ rather than but $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{4} 4 {s}^{2}$, but you can learn this and several other exceptions.......

The features the filling of the $\text{4s-orbitals}$ BEFORE the $\text{3d-orbitals}$ begin to be filled.....And thus the first-row transition metals typically have a FULL $4 s$ shell, cf. iron, $Z = 26$, and gives $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2} 3 {d}^{6}$

And given the position of the element on the Periodic Table, $\text{s-block}$, $\text{p-block}$, $\text{d-block}$, usually you can define the valence configuration without difficulty.

Anyway, this is the knowledge expected of an undergraduate student. I don't know whether you are there or at A-level.