Explain why a mole of iron atoms has more mass than a mole of helium atoms when there are the same number of atoms in a mole of each element?

A mole of iron has more mass than a mole of helium, even though they contain the same number of atoms, because 1 atom of iron has a greater mass than 1 atom of helium. It is similar to why 1 dozen bricks has a greater mass than 1 dozen roses. There are 12 items in each case, but 1 brick has a greater mass than 1 rose.