What is gram atomic mass?
Gram atomic mass is the mass of one mole of an element. It is determined by taking the atomic weight for an element on the periodic table and expressing it in grams.
So, for example, sodium (Na) has an atomic weight of 22.99 u, so it has a gram atomic mass of 22.99 grams. So one mole of sodium atoms has a mass of 22.99 g.