Atomic and Molecular Weights
Atomic weight is the averaged mass of the isotopes of elements as they appear in nature. These values are listed in any chemistry textbook; they also appear on the periodic table in the box for each element.
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14 28.08 Si silicon |
one moles of Si atoms = 28.08 g
Molecular weight (also called formula weight) is the sum of the masses of all the atoms in a compound. It is the mass, in grams, of one mole of a compound.
Example: Na2CO3, sodium carbonate. One mole contains:
2 moles of Na atoms = 2 x 23 (at. wt.) = 46 grams
1 mole C atoms = 1 x 12 (at. wt.) = 12 grams
3 moles O atoms = 3 x 16 (at. wt.) = 48 grams
molecular weight of Na2CO3 = 106 grams