Why is Vanadium 4s2 3d3 in its ground state?

[MathewsMD]

Why does Vanadium have a ground state electron configuration of 4s2 3d3 and not 3d5?

In introductory chemistry and the latter arrangement seems to be lower in energy. Why is the former configuration the actual one?

 

[SteamKing]

Vanadium is a wacky transition metal. Its electron orbital arrangement is complicated due to its position in the periodic table.

This article explains some of the quirks of how electron orbitals are filled:
http://en.wikipedia.org/wiki/Electron_configuration