Determine the amount of molecules that you have in the molecular formula. Before every molecular formula is a coefficient. This coefficient tells you how many molecules are present. If you do not see any coefficient before the molecular formula, then there is only a single molecule present. For example, if the molecular formula is C2H6, then you only have a single molecule of ethane.
Determine the number of moles that you have. You can do this by looking at the numeric subscript to the right of the element abbreviation. For example, in the formula C2H6, you have two moles of carbon and six moles of hydrogen.
Use dimensional analysis in order to determine how many atoms of each element you have. For example, in the molecular formula C2H6, you have two moles of carbon. In the first ratio, put 2 moles in the numerator, and 1 in the denominator. In the second ratio, put 6.022 x 10^23 atoms in the numerator, and 1 mole in the denominator. Multiply the ratios. You should receive an answer of 1.204 x 10^24 atoms of carbon. For hydrogen, multiply 6.022 x 10^23 by 6, because there are six moles of hydrogen. You should receive an answer of 3.613 X 10^24 atoms of hydrogen.
Write the atomic and molecular ratio for each element of the molecular formula. For example, in the formula C2H6, the ratio for carbon should be 1.204 x 10^24 atoms / 1 molecule. The ratio for hydrogen should be 3.613 x 10^24 atoms / 1 molecule. Therefore, in one molecule of ethane, there are more hydrogen atoms than there are carbon atoms.