Potassium is a mineral which appears in abundance in all living plant and animal cells. The human body uses it to promote regular heartbeat, help build muscles, help contract muscles, regulate blood pressure, and control the water balance in body tissues and cells. Calcium is a mineral that primarily functions in your body by making your bones and teeth hard. The rest is in your blood and soft tissues; it helps your muscles contract and your blood clot, and helps your nervous system work properly. According to your knowledge of atomic structure, explain why the calcium atom is smaller than potassium atom.