Mass number

The mass number or nucleon number (sometimes called core size ) is the number of nucleons, ie the heavy nucleons (protons and neutrons) of an atom of a nuclide. You are so close to the atomic mass in u ( atomic mass units). Your formula sign is in the field of mass spectrometry, however.

It is the sum of number of protons and neutrons:

Nuclides with the same number of protons but different neutrons and therefore different mass numbers are called isotopes. For example, the nucleus of the most common hydrogen isotope consisting of a single proton, that of the hydrogen isotope deuterium (heavy hydrogen ) of one proton and one neutron.

For the abbreviated representation of a particular nuclide to write the left above the respective element symbol its mass number and its atomic number on the bottom left.

The carbon isotope with mass number 14 is called so in formulas

Written.

The proton number is already defined by the element symbol and is therefore often omitted in the notation unless it is not, as in nuclear reactions are of particular interest. In running text, therefore, the notation element-name mass number (eg " uranium -235 " or " carbon-14 " ) is common, which also corresponds to the speech and does not require knowledge of the element symbols. Even the spelling of element symbol - mass number (eg "U -235 " or "C - 14") is in use.

Protons and neutrons both are among the baryons. The nucleon is therefore identical with the baryon number B of the core and also the whole atom or ion.