The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance (the decimal associated with percent of atoms of that element that are of a given isotope).Īverage atomic mass = f 1M 1 + f 2M 2 +… + f nM nwhere f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope. (Lithium also has another, rarer isotope with only 2 neutrons.) Figure: Lithium Atom: Stylized lithium-7 atom: 3 protons (red), 4 neutrons (black), and 3 electrons (blue). The word ‘isotope’ comes from the Greek ‘isos’ (meaning ‘same’) and ‘topes’ (meaning ‘place’) because the elements can occupy the same place on the periodic table while being different in subatomic construction. All elements exist as a collection of isotopes. By adding together the number of protons and neutrons and multiplying by 1 amu, you can calculate the mass of the atom. This is because each proton and each neutron weigh one atomic mass unit (amu).
For any given isotope, the sum of the numbers of protons and neutrons in the nucleus is called the mass number. These different types of helium atoms have different masses (3 or 4 atomic mass units ), and they are called isotopes. For example, stable helium atoms exist that contain either one or two neutrons, but both atoms have two protons. The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance.Ītoms of the same element can, however, have differing numbers of neutrons in their nucleus.
0 kommentar(er)
