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

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

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Answer 1 · 2017-12-31T00:48:53

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 $s$ $s$ orbital.
H $1 s^{1}$ $1s^1$
Li $[H e] 2 s^{1}$ $[He]2s^1$
Na $[N e] 3 s^{1}$ $[Ne] 3s^1$
etc…

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

However, some transition metals don't follow this rule.
For example, let's see the electronic structure of Group 8.
Fe $[A r] 3 d^{6} 4 s^{2}$ $[Ar]3d^6 color(red)(4s^2)$
Ru $[K r] 4 d^{7} 5 s^{1}$ $[Kr]4d^7 color(blue) (5s^1)$
Os $[X e] 4 f^{14} 5 d^{6} 6 s^{2}$ $[Xe] 4f^14 5d^6 color(green) (6s^2)$

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

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

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