Isotope electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that
Standard atomic weight publishes "abridged" values (up to five digits per number only), and for the twelve interval values, "conventional" values (single number values). Symbol "A" is a relative atomic mass, for example from a specific sample. To be specific, the standard atomic weight can be noted as , where (E) is the element symbol. The abridged atomic weight, also published by CIAAW, is derived from the standard atomic weight reducing the numbers to five digits (five significant figures). The name does not say 'rounded'. Interval borders are rounded "downwards" for the first (lowmost) border, and "upwards" for the "upward" (upmost) border. This