01 元素和元素周期表The number of protons in the nucleus of an atom is referred to as the atomic number, or proton number, Z. The number of electrons in an electrically neutral atom is also equal to the atomic number, Z. The total mass of an atom is determined very nearly by the total number of protons and neutrons in its nucleus. This total is called the mass number, A. The number of neutrons in an atom, the neutron number, is given by the quantity A-Z.原子核内的质子数被称为原子序数,或质子数，Z。一个电中性原子的电子数量也等于原子序数，Z。原子
