Chemical element isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50). The mass number of an element, "A", is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes
Chemical equation a 2 before O, giving the balanced equation: This equation does not have any coefficients in front of CH and CO, since a coefficient of 1 is dropped. Generally, any chemical equation involving "J" different molecules can be written as: where "R" is the symbol for the "j-th" molecule, and ν is the stoichiometric coefficient for the "j-th" molecule, positive for products, negative for reactants (or vice versa). A properly balanced chemical equation will then obey: where the composition matrix "a" is the number of atoms of element "i" in molecule "j". Any vector which, when operated upon by the