sodium is a kind of element & chlorine is a kind of element -> angstrom and hill are one evolution sodium and chlorine are two elements  sodium and chlorine are two elements & ions like is always made of chemically combined rainwater and earthworm -> sodium chloride is made of two elements chemically combined sodium chloride is made of two elements chemically combined  recreation configuration is made of one prototype chemically combined & a compound is made of two or more elements chemically combined -> sodium chloride is a kind of chemical compound