Читать книгу Geology and Mineralogy of Gemstones - Karl Wallace, David Turner R. - Страница 16

The identity of an atom is determined by the number of protons it contains – this is also called the element’s atomic number. For example, the first element of the periodic table is hydrogen (H), which has an atomic number of 1, which means it has one proton. The second element of the periodic table is helium (He), which has an atomic number of 2, which means it has two protons. Gold (Au) is an element with an atomic number of 79. Thus, each atom of gold has exactly 79 protons. Each proton carries a single positive electric charge. Unlike protons, neutrons do not follow the same strict distribution amongst elements. Usually there are about equal numbers of neutrons as protons in an atom. However, larger atoms (those with more protons) generally have a greater number of neutrons than protons. Neutrons carry no electric charge. Compared to protons and neutrons, electrons are much smaller in size. Each electron carries a single negative electric charge.