How to determine what kind of metal an element is from the periodic table

It depends on where it is on the periodic table. It is divided into sections that determine what kind of metals they are, how they react and bond, etc.

Ithink about 50 % of an original isotope's number of atoms remain

Each calcium ion has a charge of +2, which can also be written as ca2+. if those ions move out of the neuron and no other ions are moving, the neuron would lose the positive charge associated with those ions and become more negatively charged.