a substance made up of atoms of two or more different elements joined by chemical bonds

a combination of chemical symbols and numbers to represent a substance

a way to describe a chemical reaction using chemical formulas and other symbols

number after the atomic symbol in equations that tells us the number of atoms of that element in the molecule

number in front of molecules in a chemical equation; tells the number of that molecule involved in the reaction

a substance that takes part in and undergoes change during a reaction

a new material formed in a chemical reaction

protons + neutrons

a reaction in which energy is absorbed

a reaction that releases energy, usually in the form of heat.