1) A mole is defined as 6.022x10^23 atoms or molecules and can be used to convert between the number of particles and mass of a sample. 2) The molar mass of an element or compound allows conversion between moles and grams. For elements, molar mass equals atomic mass in grams. 3) Chemical formulas indicate the number of moles of each element in a mole of compound using subscripts. This allows calculation of mass or number of atoms of one constituent from the formula unit.