When electrons are removed from the outermost shell of calcium atom, its atom becomes positively charged, with a charge of plus one.
When an electron is added to an atom, the atom becomes negatively charged, with a charge of minus one.
When these atoms become positively or negatively charged, they are known as ions. Positively charged ions are called cations and negatively charged ions are called anions.
Calcium is identified as one of the cations because it is positively charged when its electrons are removed from its outermost shell.
