Rules oxidation numbers

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

Strategy First look for elements whose oxidation number is always or almost always the same (rule 3). Then solve for the oxidation number of phosphorus, applying rule 4. 

Strategy The structure can be obtained by removing an oxygen atom from H O, (Figure 21.8). Relative acid strengths can be predicted on the basis of the electronegativity and oxidation number of the central nonmetal atom, following the rules cited above. 

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 ... 

Reactions occur such that the net change of oxidation numbers is zero. (This last rule is really a result of the conservation of charge.)... 

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

The following rules apply to the determination of oxidation numbers. 

Oxidation number 851, (T) 853 rules for determining. 851 Oxidation number method 851 Oxidation-reduction cells 64 Oxidation-reduction curve 361 Oxidation-reduction indicators (T) 367 Oxidation-reduction reactions 67, 258, 360,... 

To assign an oxidation number to an element, we start with two simple rules ... 

The oxidation numbers of elements in most ot the compounds in this text are assigned by using these two rules along with the following specific values ... 

SOLUTION The process is oxidation if the oxidation number of sulfur increases, reduction if it decreases. We need to assign the oxidation numbers of sulfur in S02 and S042, then compare them. To assign an oxidation number to sulfur we represent that number by x and solve for x, by using the rules in Toolbox K.l. The oxidation number of oxygen is —2 in both compounds. 

Oxidation increases the oxidation number of an element reduction decreases the oxidation number. Oxidation numbers are assigned by using the rules in Toolbox K.l. 

A half-reaction in which the oxidation number of an element is increased. Examples 2 Mg(s) + 02(g) — 2MgO(s) (2, 3) Mg(s) - Mg2+(s) + 2 e. oxidation number The effective charge on an atom in a compound, calculated according to a set of rules (see Toolbox K.l). An increase in oxidation number corresponds to oxidation a decrease corresponds to reduction. 

In Sec. 13.2 we will learn to determine oxidation numbers from the formulas of compounds and ions. We will learn how to assign oxidation numbers from electron dot diagrams and more quickly from a short set of rules. We use these oxidation numbers for naming the compounds or ions (Chap. 6 and Sec. 13.4) and to balance equations for oxidation-reduction reactions (Sec. 13.5). In Sec. 13.3 we will learn to predict oxidation numbers for the elements from their positions in the periodic table in order to be able to predict formulas for their compounds and ions. 

With these rules, we can quickly and easily calculate the oxidation numbers of an element most of the time from the formulas of its compounds. 

Cl has an oxidation state of - I (rule 7). I has an oxidation number of +3 (rule 1). I is not -1 because it is combined with a halogen higher in the periodic table. 

The rules above gave maximum and minimum oxidation numbers, but those might not be the only oxidation numbers or even the most important oxidation numbers for an element. Elements of the last six groups of the periodic table for example may have several oxidation numbers in their compounds, most of which vary from each other in steps of 2. For example, the major oxidation states of chlorine in its compounds are -1, +1, +3, +5, and +7. The transition metals have oxidation numbers that may vary from each other in steps of 1. The inner transition elements mostly form oxidation states of + 3, but the first part of the actinoid series acts more like transition elements and the elements have... 

Draw an electron dot diagram for H,0,. Assign an oxidation number to oxygen on this basis. Compare this number with that assigned by rule 6 (Sec. 13.2). 

Ans. Rule 2 Uncombincd elements have zero charges, and so the oxidation numbers must add up to 0. Since all the atoms are the same, all the oxidation numbers must be the same—0. Rule 3 Monatomic ions have the oxidation numbers of all the atoms add up to the charge on the ion. Since there is only one atom (monatomic), the oxidation number of that atom must add up to the charge on the ion that is. it is equal to the charge on the ion. 

The oxidation number, or oxidation state, is the formal charge on an atom calculated on the basis that it is in a wholly ionic compound. Oxidation numbers are assigned according to several rules. 

Furthermore, according to (4.9a) the total number of covalent M—L bonds (n + m, both oml and 7TMl) is 10 — k. Because main-group ligands generally are more electronegative than the central transition-metal atom, each such covalent M—L bond can be termed a formal one-electron oxidation of M. The duodectet-rule-conforming oxidation number ( ox) of M is therefore... 

The central sulphur has eight bonds. The ion has an overall charge of —2. The oxidation number of the sulphur is therefore 8 — 2 = +6. We generally indicate oxidation numbers with roman numerals, though, so we write S(VI). Table 2.10 lists the rules required to assign an oxidation number. 

Another way to determine what is undergoing oxidation and what is undergoing reduction is by looking at the change in oxidation numbers of the reactant species. Oxidation occurs when there is an increase in oxidation number. In the example above, the Zn metal went from an oxidation state of 0 to +2. Reduction occurs when there is a decrease in oxidation number. Cu2+ went from an oxidation state of +2 to 0. In order to determine if a particular reaction is a redox reaction, determine the oxidation numbers of each element in the reaction. If at least one element changes oxidation number, it is a redox reaction. Refer to your textbook for rules in assigning oxidation numbers. 

To balance a redox reaction using the oxidation number method, follow the following rules ... 

As we shall see, it is useful to be able to determine the oxidation number of a given element in a compound. Since most elements can exist in a variety of oxidation states, it is necessary to adopt a set of rules or guidelines for this determination. These are listed in Table 5.5. 

A discussion of several examples should clarify the general scheme. First, rules 1 through 9 cover many situations in which, with few exceptions, the oxidation number is a set number. For example, in BaCl2, barium is +2 (rule 3) and Cl is -1 (rule 5). In K20, potassium is +1 (rule 2) and O is -2 (rule 8). In CaH2, calcium is +2 (rule 3) and H is -1 (rule 7). 

Next, rule 10 is used for determining all oxidation numbers of all elements that rules 1 through 8 do not cover (this must be all but one element in a formula), and then assigning the remaining elements oxidation numbers, knowing that the total must add up to either zero or the ionic charge. 

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