Or proton number; The number (symbol Z) of protons in the nucleus of an atom. It is equal to the positive charge on the nucleus. In a neutral atom, it is also equal to the number of electrons surrounding the nucleus. The 109 elements are arranged in the periodic table of the elements according to their atomic number. See also nuclear notation.
The order of an element in Mendeleyev's table of the elements; equal to the number of protons in the nucleus or electrons in the neutral state of an atom of an element.
The number of protons in a nucleus. It determines the chemical properties of an element.