# Why are transition metals said to have different valencies?

I understand that the term valency refers to the number of bonds an element would be able to form with either chlorine or hydrogen. If this is directly related to the number of valence electrons an atom has, why do transition metals have variable valencies?

• Only maximum valency is, no one says there can't be unpaired electrons or lone pairs. Also valency is rather primitive concept, coordination number is better, but still not perfect. – Mithoron Aug 21 '16 at 0:28
• The concept of valence electrons doesn't really work for transition metals. – f'' Aug 21 '16 at 1:06

I think it's kind of a poor use of terms here. When talking about transition metals, the valency generally refers to the oxidation state of the metal atom. E.g: hexavalent chromium is $\ce{Cr^6+}$, not necessarily a chromium bonded to six other things.
• You can (and should!) use mhchem to format chemical expressions: typing $\ce{Cr^6+}$ renders as $\ce{Cr^6+}$. Nitpicking, I would say that hexavalent chromium is Cr(VI), not $\ce{Cr^6+}$ as the latter implies a naked ion with a 6+ charge. – orthocresol Aug 21 '16 at 8:33