35 which element reacts with oxygen to form ionic bonds? (1) calcium (3) chlorine
(2) hydrogen (4) nitrogen

Calcium reacts with oxygen to form an ionic bond. An ionic bond by definition is the kind of chemical bond formed when there is a complete transfer of valence electrons from one atom to another, generating two oppositely charged ions. In ionic bonding, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons and becomes a negatively charged anion. Calcium has two electrons in its valence or outermost shell while oxygen has 6 electrons. Calcium gives up these two electrons and becomes positively charged and oxygen accepts them and becomes negatively charged forming an ionic bond resulting in a new compound called calcium oxide.

Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place.