Explain why calcium only has one oxidation state, other than zero, while manganese has several oxidation states

Question

anonymous · Answer

Manganese is a transition metal, which means it has electrons in the 3d subshell that lie close in energy to the valence (outermost) 4s hell.  That means with small changes in energy, you can remove more electrons than just the two 4s valence electrons.  Depending on the exact configuration of ligands (things attached to the Mn atom), and the precise electric field they generate, you can have many different charge states of the Mn atom that are stable.

One the other hand, Ca has two 4s valence electrons, and then after that a closed n=3 shell which is very stable -- looks like an argon atom.  Once you strip off those two valence electrons, it is very hard to form any other ion of Ca that is stable.