Simple problem regarding Gram-atom concept

So if I recall,Gram atom is mass of mono atomic elements in grams which will contain 1 mole of its elements like Carbon which is 12 am 1 mole so it's 12 g/mol.
Ok but the thing I dont get is the definition is *Monoatomic elements*.But what about Cl2 and other non mono elements.
Isin't Cl2 supposed to be in g/mol as well but the definition states monotonic elements.Pls clarify

1 mol of any substance contains an Avogadro number of particles of that substance.
A diatomic element such as hydrogen has two atoms in its smallest particle (the molecule), so that the mass 1 mol of hydrogen = 2g
1 mol of hydrogen (molecules) comprises 2 mol of hydrogen atoms.