# Is the number of valence electrons the same for all elements within a group on the periodic table?

Dec 31, 2017

This is not always true.

#### Explanation:

For main group elements, the number of valence electrons is the same in every element in the same group.

[Example]
Group 1 elements have 1 valence electron in the $s$ orbital.
H $1 {s}^{1}$
Li $\left[H e\right] 2 {s}^{1}$
Na $\left[N e\right] 3 {s}^{1}$
etc…

Group 16 elements have 6 valence electrons in $s$ and $p$ orbitals.
O $\left[H e\right] 2 {s}^{2} 2 {p}^{4}$
S $\left[N e\right] 3 {s}^{2} 3 {p}^{4}$
Se $\left[A r\right] 3 {d}^{10} 4 {s}^{2} 4 {p}^{4}$

However, some transition metals don't follow this rule.
For example, let's see the electronic structure of Group 8.
Fe $\left[A r\right] 3 {d}^{6} \textcolor{red}{4 {s}^{2}}$
Ru $\left[K r\right] 4 {d}^{7} \textcolor{b l u e}{5 {s}^{1}}$
Os $\left[X e\right] 4 {f}^{14} 5 {d}^{6} \textcolor{g r e e n}{6 {s}^{2}}$

The electronic sturcture of iron, ruthenium and osmium are cited from WebElements (https://www.webelements.com/).