I know that metals have the capability to lose electrons and form cations, but is it also theoretically possible to supply an electron to a metal so that it forms an anion? If so, has it ever been done? I referred this question (Can two metals combine to form a compound?) but could not get a sati...

As the title suggests, I can't understand why certain kinds of variations (like Face-centred or Body-centred) are restricted to certain types of unit cells. An orthorhombic unit cell has Primitive, Body-centred, Face-centred and End-centred variations, why can't the same be applicable to other cr...