There are two electrons in the outer shell of calcium. All other elements in the same vertical row on the periodic table also have two electrons in their outer shell.
Calcium has the atomic number of 20 and the chemical symbol is Ca. It has an atomic mass of 40.08. Calcium is often found in compounds such as marble and limestone. Calcium is also found in the bones and teeth of humans and animals. Calcium also appears in dietary supplements, beverages and many foods. This includes leafy greens, cheese and some fish. Calcium is vital in order to maintain a person's health.