This helps determine the oxidation state of any one element in a given molecule or ion assuming that we know the common oxidation states of all of the other elements. Use the periodic table to determine the atomic mass of each element in the molecule. Chemistry Elements Compounds And Mixtures Classified as a transition metal Nickel is a solid at room temperature. How to determine element or compound . First determine how the compound splits apart into ions when it dissolves. The oxidation number of a monatomic ion equals the charge of the ion. The oxidation number of O in compounds is usually -2 but it is -1 in peroxides. The oxidation number of H is 1 but it is -1 in when combined with less electronegative elements. This step-by-step tutorial shows how to calculate the empirical and molecular formulas for a compound. Determine the atomic weight of element M and identify it by name. The oxidation number of a free element is always 0. The chloride of an unknown met