How can I find valence electrons of transition metals?
Most transition metals have 2 valence electrons.
Valence electrons are the sum total of all the electrons in the highest energy level (principal quantum number n). Most transition metals have an electron configuration that is
For example. How many valence electrons are there in Fe?
Solution: 2 valence electrons.
Reason: The electron configuration of Fe is
Copper and chromium have one valence electron (they are exceptions), because they have one 4s electron. Chromium has an electron configuration of
It is easier and more practical to describe which orbitals are valence orbitals when it comes to transition metals (although it gets difficult with lanthanides and actinides).
In general, the first-row transition metals have a set of valence orbitals that include their
- Scandium makes sense to have up to three valence electrons, since a
#"Sc"^(+3)#oxidation state exists (e.g. #"ScCl"_3#), but not #"Sc"^(+4)#or higher. A #+3#oxidation state would have required transferring three valence electrons if it were to form a pure cation.
- Chromium could have up to six valence electrons, which would include its
#3d#electrons, since it can accomplish a #+6#oxidation state (i.e. in #"Cr"_2"O"_7^(2-)#, or in #"CrO"_4^(2-)#).
- Copper tends to have a
#+1#oxidation state (e.g. #"CuCl"#), so it makes sense that it uses its one #4s#electron most often as its valence electron(s). But a #+2#oxidation state is also known (e.g. #"CuCl"_2#), and so it is capable of taking from its #bb(3d)#electrons as well for its valence electron(s).
On the other hand, we could easily say that the valence ORBITALS of the first-row transition metals are the
So in general, I would say the number of valence electrons for transition metals (and lanthanide and actinides) vary in an unpredictable way, but the valence orbitals could sometimes be predicted with enough chemical intuition.
DISCLAIMER: It is, however, in general difficult for the lanthanides and actinides to predict which orbitals are valence.
For example, the actinides have