I am trying to find out how many atoms are in 1.5 moles of flourine gas.?

The answer is 1.81 x 10 (24th) but my calculations give me 9.03 to x 10(23rd). This has something to do I think with it being a diatomic element. Can someone help me adusting the formula. Please no shorthand. Assume I am in Chem 101 and would not understand if you skip a step you take for granted.