Conversion of Atomic Masses

This is a calculator for converting the atomic masses of the elements of the periodic table, from hydrogen (1) to curium (96). Enter a mass in one field and click 'Calculate', all other masses will be calculated. The masses have the unified atomar mass unit u, which is 1.660538782 *10^-24 gramms or 1/12 of the mass of one C¹²-atom. However, any other mass unit, or even mol, can stand for u. For example, one mol He (helium) has the same mass as 3.971 mol H (hydrogen). The average atomic mass of each element on earth is used.

Atoms consist of protons and neutrons in their nuclei, and electrons in their shells. Protons and neutrons together are called nucleons, the building blocks of the nucleus. Electrons contribute very little to the total mass; a nucleon is about 2000 times more massive than an electron. On average, a neutron has slightly more mass than a proton.
Chemical elements have different isotopes, which differ in the number of neutrons they contain and thus in their mass. Most elements also have several naturally occurring isotopes; only a few, such as gold, are pure elements, of which there is only one natural isotope. For all other elements, the masses are the weighted averages of the naturally occurring isotopes, with the weighting of course corresponding to their abundance. This is one reason why the mass of the atoms is not an integer.
Another reason is the following: a single proton or neutron always has the same rest mass, but bound in different atomic nuclei, they have different masses. The isotope iron-56 has the lowest mass per nucleon, with a value of 0.998838 u. This isotope has the most energetically advantageous nucleus. Very small and very large nuclei have noticeably higher energies per nucleon and thus also higher masses.