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

1 Answer
yumean1119
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 #1s^1#
Li #[He]2s^1#
Na #[Ne] 3s^1#
etc…

Group 16 elements have 6 valence electrons in #s# and #p# orbitals.
O #[He]2s^2 2p^4#
S #[Ne] 3s^2 3p^4#
Se #[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 #[Ar]3d^6 color(red)(4s^2)#
Ru #[Kr]4d^7 color(blue) (5s^1)#
Os #[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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