How to Find the Mass of Atoms

Find the element of the atom for which you want to determine mass on the periodic table. Almost all elements on the periodic table are noted by a one- or two-letter symbol: H is hydrogen, He is helium, Na is sodium and Hg is mercury, for example. Refer to the list in the references section of this article if you're not sure of your element's symbol.

Identify the atomic mass associated with your chosen element on the periodic table, a number listed below the element's symbol. These numbers are the masses of one atom of that element in atomic mass units, a special unit of measure that's about equal to the mass of a single proton or neutron. Electrons have masses only a minute fraction of that of protons and neutrons -- it takes about 2,000 electrons to equal the mass of a single proton -- and generally are not considered in atomic weight. Hydrogen's atomic mass is 1.008, for example, and helium's is 4.003. Don't confuse the atomic mass with the atomic number, which is listed above the element's symbol and indicates the number of protons in an atom.

Convert the atom's atomic mass from atomic mass units to grams. Using a scientific calculator, divide the atomic mass by 6.023 x 10^23, a special constant known as Avogadro's number. This constant refers to the number of atoms or molecules in a special chemistry measurement known as a mole. Using this formula, the weight of a single hydrogen atom, for example, would be about 1.67 x 10^-24 g -- or written out, 0.00000000000000000000000167 g.

Convert your atom's measurement in grams into your preferred measurement unit. Divide by 1,000 -- meaning you simply subtract 3 from the exponent -- to express in kilograms, for example, or divide by 453.6, the number of grams in a pound, to express in pounds. The cleanest metric measurement for indicating the mass of atoms is the yoctogram, equivalent to one septillionth, or 10^-24, of a gram. The hydrogen atom, for example, has a mass of about 1.67 yoctograms.