|at. no., Z, Also called: proton number the number of protons in the nucleus of an atom of an element|
at. no. or at no
atomic number n.
Abbr. at. no., at no
The number of protons in an atomic nucleus; it indicates the position of an element in the periodic table.
The number of protons in the nucleus of an atom. In electrically neutral atoms, this number is also equal to the number of electrons orbiting about the atom's nucleus. The atomic number of an element determines its position in the Periodic Table, and is usually denoted by the letter Z and written as a subscript before an element's symbol, as in 92U.
The number of protons or electrons normally found in an atom of a given chemical element. The higher the atomic number, the heavier the atom is. In a neutral atom, the number of protons and electrons is the same. (See atomic weight and periodic table of the elements.)