Nonmetals oxidation number

The transition metals, unlike those in Groups 1 and 2, typically show several different oxidation numbers in their compounds. This tends to make their redox chemistry more complex (and more colorful). Only in the lower oxidation states (+1, +2, +3) are the transition metals present as cations (e.g., Ag+, Zn2+, Fe3+). In higher oxidation states (+4 to +7) a transition metal is covalently bonded to a nonmetal atom, most often oxygen. 

Strategy Referring to Table 21.3, find an oxide in which the central nonmetal atom has the same oxidation number as in the acid. 

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. 

Note that, in general, the highest oxidation number of a nonmetal is given by the second digit of its group number (17 for Cl, 16 for S, 15 for N). 

The oxidation number of hydrogen is +1 in combination with nonmetals and —1 in combination with metals. 

A typical reaction of the nonmetal halides is their reaction with water to give oxoacids, without a change in oxidation number ... 

The interhalogens have properties intermediate between those of the constituent halogens. Nonmetals form covalent halides metals tend to form ionic halides. The oxoacids of chlorine are all oxidizing agents both acidity and oxidizing strength of oxoacids increase as the oxidation number of the halogen increases. 

Rationalize the properties of the oxides and oxoacids of the nonmetals in terms of the oxidation number of the nonmetal and the identification of acid anhydrides. 

Stable binary ionic compounds are formed from ions that have noble gas configurations. None of the compounds meet this requirement. First of all, C04 is not an ionic compound at all because it is a covalent compound, made from 2 nonmetals. Even so, C04 is not stable because with O2, C would have an oxidation number of +8, which is very unlikely. Consider the following ionic compounds composed of a metal and... 

A number of substances react vigorously with water, sometimes with the formation of hydrogen gas, which itself may ignite in the presence of air. Examples or such reactants are alkali metals, finely divided light metals and their hydrides, anhydrous metal oxides, anhydrous metal halides, nonmetal halides, and nonmetal oxides as well as certain organics such as anhydrides... 

Hydrogen is capable of forming compounds with all elements except the noble gases. In compounds with nonmetals, hydrogen usually behaves like a metal instead of a nonmetal. Therefore, when hydrogen combines with a nonmetal, it usually has a +1 oxidation number. When hydrogen combines with a metal, it usually has a —1 oxidation number. Hydrogen compounds with the transition metals are usually nonstoichiometric. Nonstoichiometric compounds have no definite formula. 

A nonmetal may adopt any oxidation number between the values predicted in the preceding two paragraphs. The only exceptions are fluorine, which is only -1 in compounds, and helium, neon, and argon, which have no known compounds. When there is a choice of oxidation states, there must be additional information available in order to allow you to choose the correct state. 

Chemically, nonmetals are usually the opposite of metals. The nonmetallic nature will increase towards the top of any column and toward the right in any row on the periodic table. Most nonmetal oxides are acid anhydrides. When added to water, they will form acids. A few nonmetals oxides, most notably CO and NO, do not react. Nonmetal oxides that do not react are neutral oxides. The reaction of a nonmetal oxide with water is not an oxidation-reduction reaction. The acid that forms will have the nonmetal in the same oxidation state as in the reacting oxide. The main exception to this is N02, which undergoes an oxidation-reduction (disproportionation) reaction to produce HN03 and NO. When a nonmetal can form more than one oxide, the higher the oxidation number of the nonmetal, the stronger the acid it forms. 

In compounds, hydrogen has an oxidation number of -i-l when it bonds to nonmetals (as in H2O) and an oxidation number of -1 when it bonds to metals (as in NaH). 

Now we can work out the formula of an ionic compound formed between the monatomic ions of two main-group elements, one a metal and the other a nonmetal. Unless a lower oxidation number is specified (as for the p-block metals), the metal atom loses all its valence electrons, and the nonmetal atom gains enough electrons to complete its valence shell. Then we adjust the numbers of cations and anions so that the resulting compound is electrically neutral. A simple example is calcium chloride. The calcium atoms ([Ar]4s2) each lose two electrons, to form... 

The important compounds of nitrogen with hydrogen are ammonia, hydrazine, and hy dr azoic acid, the parent of the shock-sensitive azides. Phosphine forms neutral solutions in water reaction of nonmetal halides with water—hydrolysis—produces oxoacids but no change in oxidation number. 

In general, the farther left an element is in the periodic table, the more likely it is that the atom will be "cationlike." Metals, therefore, usually have positive oxidation numbers. The farther right an element is in the periodic table, the more likely it is that the atom will be "anionlike." Nonmetals, such as O, N, and the halogens, usually have negative oxidation numbers. We ll see the reasons for this trend in Sections 63-6.5. 

The acid-base properties and the ionic-covalent character of an element s oxide depend on both the element s position in the periodic table and its oxidation number. As Figure 14.6 shows, both the acidic character and the covalent character of an oxide increase across the periodic table from the active metals on the left to the electronegative nonmetals on the right. In the third row, for example, Na20... 

Both catalytic and stoichiometric oxidations of substrates by metal-dioxygen complexes are known.147-150 For example, stoichiometric oxidations of a number of nonmetal oxides occurs readily380 381a> b ... 

Metals with high oxidation numbers tend to act somewhat like nonmetals. For example, many transition metals form oxoanions, such as permanganate ion, chromate ion, and dichromate ion, in which the metal is covalently bonded to oxygen. The ability to form covalent bonds to oxygen is evidence of these metals more covalent nature. (In their low oxidation states, most metals typically exist in ionic compounds as monatomic cations.) Titanium(lV) chloride is an example of a compound in which the... 

Oxidation number is a periodic property. For example, for most elements the maximum oxidation number is equal to the classical group number, and the minimum oxidation number for nonmetals other than hydrogen is the group number minus 8. 

In Chap. 6 we placed Roman numerals at the ends of names of metals to distinguish the charges on monatomic cations. It is really the oxidation number that is in parentheses. This nomenclature system is called the Stock system. For monatomic ions, the oxidation number is equal to the charge. For other cations, again the oxidation number is used in the name. For example, Hg2 + is named mercury(I) ion. Its charge is 24- the oxidation number of each atom is 4-1. Oxidation numbers are also used for other cations, such as dioxovanadium(V) ion, V02". The prefix 0x0- stands for oxygen. Oxidation numbers can be used with nonmetal-nonmetal compounds, as in sulfur(VI) oxide for SO3, but the older system using prefixes (Table 6-2) is still used more often. 

In order to write a chemical formula for compounds, the names of their ions should be known. The oxidation number of some important metals and nonmetals is given in Table 1. 

Table 1 The oxidation number of some important metals and nonmetals...

The ratio of ions must be such that the number of electrons lost by the metal is equal to the number of electrons gained by the nonmetal. Because the sum of the oxidation numbers of these ions is zero, these ions must be present in a one-to-one ratio. One sodium ion transfers one electron to one chloride ion, and the formula unit is NaCl. 

Many elements other than those specified in the rules above, including most of the transition metals, metalloids, and nonmetals, can be found with different oxidation numbers in different compounds. For example, the two copper compounds and the two chromium compounds shown in Figure 20-5 a and b, respectively, have different oxidation numbers. 

MgO]—Magnesium, an alkaline earth metal with two valence electrons, has an oxidation number of + 2. Oxygen, a nonmetal with six valence electrons, has an oxidation number of -2. They combine in a 1 1 ratio because +2 + -2 = 0. 

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