Definitions of molecular mass, molecular weight, molar mass and molar weight In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all … Composition of 鈉 - Na . ››More information on molar mass and molecular weight. The free metal does not occur in nature, and must be prepared from compounds. Its only stable isotope is Na. Element Symbol Atomic Mass # of Atoms Mass Percent; Sodium: Na: 22.9898 g/mol: 1: Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and rock salt(NaCl). Examples of molecular weight computations: C[14]O[16]2, S[34]O[16]2. Computing molecular weight (molecular mass) To calculate molecular weight of a chemical compound enter it's formula, specify its isotope mass number after each element in square brackets. Many salts of sodium are highly water-soluble: sodium ions hav… It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Sodium is a chemical element with the symbol Na (from Latin "natrium") and atomic number 11. The molar mass and molecular weight of Na is 22.9898.