Valence Electrons in the d-orbitals

[TiffanyL1G]

How do you know how many valence electrons are in the d orbitals, since 4s2 is technically the "outer most" orbital? Would all d orbital elements be either one or two depending on 4s? Or do we add the d orbital and the s orbital together? For example, would Iron (Fe) have six valence electrons, 2 valence electrons, or eight valence electrons?

[Josephine Chan 1B]

Transition metals are a little bit different. For transition metals like iron, the amount of valence electrons they have depends on the number of electrons they have after the noble gas core. So for iron: [Ar] 4s^2 3d^6, there are 8 electrons after the noble gas core so it has 8 valence electrons.

[Julia Go 2L]

Adding on, transition metals have incomplete d sub shells, which can actually be used for bonding. Since they can be used for bonding, they should be included as valence electrons.

For example, the electron configuration of Manganese is:

[Ar] 3d^5 4s^2

Although the outer shell is 4s, the electrons in the 3d sub shell are also included as valence electrons. There are 7 valence electrons total.