Introduced the concept of the mole, a unit used in chemistry. Like a dozen, it is a word that means a specific number of things. A mole is equal to 6.022 x 1023 basic particles, such as atoms, molecules, ions, or electrons. So a mole of copper metal contains 6.022 x 1023 atoms of copper. A mole of water contains 6.022 x 1023 molecules of water.
The mole is the number of atoms of C-12 that have a mass of exactly 12 grams – the same value for the mass of a single C-12 atom in amu. Since the masses on the periodic table are relative, that means that a mole of an element weighs, in grams, the atomic mass of that element from the periodic table. This is known as the “molar mass” – the mass of one mole. The mass of a mole of a compound can be found by adding the molar masses of the elements that the compound is made of.
So, a mole of hydrogen atoms weighs 1.008 g. A mole of oxygen atoms weighs 16.00 g. A mole of water, which is comprised of 2 H and one O, would weigh 2(1.008) + 16.00 = 18.02 g.
The molar mass of a covalent (molecular) compound is sometimes referred to as the molecular mass or molecular weight. These terms mean the same thing as molar mass – the mass of one mole of the substance.


