ABSTRACT
Let us make a few observations about these rules before we look at some examples of their use . First, in Rule 1 the uncombined element is an element that is in the free elemental state, or the state of the element when it is not combined with any other element . For most elements, this is shown by the use of the symbol of the element, as found in the periodic table . For example, the oxidation numbers of silver metal (Ag), radon gas (Rn), and mercury liquid (Hg) would be 0 . However, there are some elements whose free elemental state refers to diatomic molecules, or molecules that consist of two atoms of the element that are covalently combined . This list includes hydrogen gas (H2), fluorine gas (F2), nitrogen gas (N2), oxygen gas (O2), chlorine gas (Cl2), bromine liquid (Br2), and iodine solid (I2) . Thus, whenever these diatomic symbols are observed, these substances are in their free elemental state and the correct oxidation number to be assigned would be 0 .
