How did we figure out the molar masses of elements?

First we found the AMUs (1 12th mass of carbon?) but how did we get to the mass of the moles??? AND!!! How can one molecule of gas at STP occupy the SAME VOLUME as one mole of the same gas!!!!!! HELP!!!! (eg: 1molecule of O2 occupies 24.79 L and 1 mol of O2 ALSO 24.79!!!!) HELP!!!! ME!!!!!How did we figure out the molar masses of elements?
Look at the periodic table. Whatever it says is the mass in amu is the molar mass of the element. For instance my periodic table says Carbon has a mass of 12.011 amu so Carbon has a molar mass of 12.011 g/mol(Different periodic tables might have slightly different numbers for the molar mass but it shouldn't be significantly different)





One mole of any gas occupies 22.4 Liters at STP. This is known as Avogrado's hypothesis. One molecule of a gas should not occupy the same volume so I think you're wrong about that.How did we figure out the molar masses of elements?
the molar mass is just the gram formula mass.





for example, the molar mass of carbon is 12.0111grams, and this is one mole. it's one mole of carbon. so this means 24.0222 grams of carbon is 2 moles of carbon.





I don't really understand your next question, but one mole equals 6.022 x 10to the 23rd power molecules/atoms.





check out the site i listed. it summarizes what i explained.