The number, equal to the number of protons in an atom that determines its chemical properties. Symbol: Z
The number of protons in an atomic nucleus. Number of a chemical element in the systematic, ordered sequence shown in the periodic table. The elements are arranged in order of increasing number of protons in the nucleus of the atom (the same as the number of electrons in the neutral atom), and that number for each element is its atomic number
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