In a chemical reaction equation,it is more convenient to use quantity of substance in number of its molecules or atoms rather than their masses,so we use a new unit calledMOLE.MoleIf we weigh an element equal to its atomic mass in grams,then it contains 6.022×1023atoms of the element.The gram atomic mass of the element as well as 6.022×1023atoms of the element, both represent 1 mole of element.1 mole of any species (atoms,molecules,ions) is equal to its atomic mass or molecular mass in grams.