Oxidation numbers assignment

An additional problem with oxidation number assignments of nitrosyl compounds is the fact that the International Union of Pute and Applied Chemistry has recommended that NO should be viewed as a neutral ligand, analogous to CO See International Union of Pure and Applied Chemistry, Nomenclature of Inorganic Chemistry, Definitive Rules (2" Edition) Section 7.323. 

Oxidation numbers assigned to elements keep track of the changes in the loss and gain of electrons. 

Count the number of electrons assigned to each atom and subtract that number from the number of electrons in the neutral atom the result IS the oxidation number... 

A neutral carbon atom has four valence electrons Five electrons are assigned to the CH2OH carbon therefore it has an oxidation number of -1 Seven electrons are assigned to the CH3 carbon therefore it has an oxidation number of-3 As expected this method gives an oxidation number of -2 for oxygen and +1 for each hydrogen... 

Notice that this generalization follows naturally from the method of calculating oxidation numbers outlined in Table 2.5. In a C—C bond one electron is assigned to one carbon, the second electron to the other. In a bond between carbon and some other element, none of the electrons in that bond ar e assigned to car bon when the element is more electronegative than carbon both are assigned to carbon when the element is less electronegative than carbon. 

Oxidation number (Section 2.19) The formal charge an atom has when the atoms in its covalent bonds are assigned to the more electronegative partner. 

The concept of oxidation number is used to simplify the electron bookkeeping in redox reactions. For a monatomic ion (e.g., Na+, S2 ), the oxidation number is, quite simply, the charge of the ion (+1, —2). In a molecule or polyatomic ion, the oxidation number of an element is a pseudo-charge obtained in a rather arbitrary way, assigning bonding electrons to the atom with the greater attraction for electrons. 

In practice, oxidation numbers in all kinds of species are assigned according to a set of four arbitrary rules ... 

Certain elements have the same oxidation number in all or almost all their compounds. The Group 1 metals always exist as +1 ions in their compounds and hence are assigned an oxidation number of +1. By the same token, Group 2 elements always have oxidation numbers of +2 in their compounds. Fluorine always has an oxidation number of — 1. 

Oxygen is ordinarily assigned an oxidation number of —2 in its compounds. (An exception arises in compounds containing the peroxide ion, 022-, where the oxidation number of oxygen is —1.)... 

Click Coached Problems for a self-study module on assigning oxidation numbers. 

Hydrogen in its compounds ordinarily has an oxidation number of +1. (The major exception is in metal hydrides such as NaH and CaH2, where hydrogen is present as the H ion and hence is assigned an oxidation number of — 1.)... 

You have to assign oxidation numbers to decide how many electrons to use. 

This arbitrary scheme of assigning oxidation numbers turns out to be quite useful, provided we don t forget that the oxidation number is a fictitious charge. We can see the usefulness by considering a reaction related to the oxidation of HS03. ... 

For the present, we will limit ourselves to molecules containing hydrogen and/or oxygen along with the element to which we wish to assign an oxidation number. The rules we will utilize are as follows ... 

First, we assign oxidation numbers to each element, using rules 1-5. We find... 

Sulfur reacts with molecular oxygen to form compounds in which sulfur is assigned positive oxidation numbers, +4 and +6. The reactions are those used in the manufacture of sulfuric acid (see Chapter 13) ... 

Chemists have found a way to keep track of electrons by assigning an oxidation number to each element. The oxidation number is defined so that... 

When an element is part of a compound or a polyatomic ion, we assign its oxidation number by using the procedure in Toolbox K.l. 

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