Question

why are cations smaller than elements that they are formed from

Answer 1

Cations are positive ions. This means that they lose electrons, Think of the atom(any atom) as a giant popcorn ball. When you take away some popcorn from the outside of the ball, it obviously get smaller. Well the same goes for atoms. The electrons are the outside of the atoms, and when you take some away the whole ball of the atom gets smaller.