Electron configuration of transition metals

[leroyjenkens]

So, for example, copper has an electron configuration of 4s1 3d10. I don't understand why 1 electron gets taken from the 4s orbital and gets added to the 3d orbital.

This configuration is more stable, apparently. Why is it more stable to have a half-filled 4s orbital?
And is there any pattern to it to where I can just figure it out for myself what the electron configuration of a transition metal is without having to look at a periodic table?

Thanks.