Charge on monatomic ions

In Chapter 6, we learned how to name cations. In the Stock system, the charges on monatomic ions were used to distinguish between different ions of the same element. For example, Cu and Cu are named copper ion and copper(ll) ion, respectively. The Roman numeral actually represents the oxidation number, not the charge on the ion. Of course, for monatomic ions, the charge is equal to the oxidation number, and thus we used the charge to determine which Roman numeral to use. By using oxidation numbers, however, we can extend our compound-naming ability to include compounds other than those of monatomic ions. For example, Hg2 is called the mercury(I) ion because the oxidation number of each mercury atom is +1. 

Some of the elements have electron configurations that differ slightly from what our general procedure would lead us to predict. You can read more about these at the textbook s Web site. The Web site also shows you how to predict charges on monatomic ions and how to write their electron configurations. 

Where there can be more than one possible charge for a given metal, Roman numerals are often used in the names in order to differentiate. For example, in this list, the names of the two iron ions are Iron(II) and Ironflll) and the names of the two copper ions are Copper(I) and Copper(II). The charges on monatomic ions are also their so-called oxidation number. More is presented on oxidation numbers in Chapter 13. 

FIGURE C.7 The typical monatomic anions formed by a selection of elements in the periodic table. Notice how the charge on each ion depends on its group number. Only the nonmetals form monatomic anions under common conditions. 

Naming of the positive ion depends on whether the cation is monatomic (has one atom). If not, the special names given in Sec. 6.3.2 are used. If the cation is monatomic, the name depends on whether the element forms more than one positive ion in its compounds. For example, sodium forms only one positive ion in all its compounds—NaT Iron forms two positive ions—Fc2r and Fe,+. Cations of elements that form only one type of ion in all their compounds need not be further identified in the name. Thus, Na may simply be called the sodium ion. Cations of metals that occur with two or more different charges must be further identified. Fe(NO,)2 and Fe(NO,)3 occur with Fc2+ and Fe3 ions, respectively. If we just call the ion the iron ion, we will not know which one it is. Therefore, for monatomic cations, we use a Roman numeral in parentheses attached to the name to tell the charge on such ion. (Actually, oxidation numbers are used for this purpose, but if you have... 

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. 

For simple monatomic ions, the oxidation number is equal to the charge on the ion. 

In CU2S, the two copper ions are balanced by one sulfide ion with a 2 charge the charge on each copper ion must be 1 +. In CuS, only one copper ion is present to balance the 2- charge on the sulfide ion the charge on the copper ion is 2 +. Note that the Roman numerals in the names of monatomic cations denote the charges on the ions. The Arabic numerals appearing as subscripts in formulas denote the number of atoms of that element present per formula unit. Either of these numbers can be used to deduce the other, but they are not the same ... 

The oxidation number of a monatomic ion is equal to the charge on the ion. This rule is also a corollary of rule 1. If the sum of all the oxidation numbers is equal to the charge and there is only one oxidation number because there is only one atom, then that oxidation number must equal the charge on the monatomic ion. 

Oxidation numbers (also called oxidation states) are used as a sort of bookkeeping method for keeping track of the electrons in polyatomic ions or compounds that have covalent bonds. (For monatomic ions, the charge on the ions works just as well.) Oxidation number is defined as the number of electrons in a free atom minus the number controlled by that atom in the compound. The control of electrons in a covalent bond is assigned to the more electronegative atom of the bond. Eight simple rules can be used to determine the oxidation number of an element from the formula of its compound or ion (Section 16.1). 

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. 

The names of monatomic cations always start with the name of the metal, sometimes followed by a Roman numeral to indicate the charge of the ion. For example, Cu is copper(l), and Cu is copper(ll). The Roman numeral in each name represents the charge on the ion and allows us to distinguish between more than one possible charge. Notice that there is no space between the end of the name of the metal and the parentheses with the Roman numeral. 

For ions composed of only one atom (that is, monatomic ions) the oxidation number is equal to the charge on the ion. Thus Li+ has an oxidation number of +1 Ba ion, +2 Fe, +3 1 ion, 1 ion, 2 and so on. All alkali metals have an oxidation number of +1 and all alkaline earth metals have an oxidation number of +2 in their compounds. Aluminum has an oxidation number of +3 in all its compounds. 

The simplest ions are monatomic. A monatomic ion is an ion formed from a single atom. Table 2.4 lists common monatomic ions of the main-group elements. You may want to look at the table while you read first the rules for predicting the charges on such ions and then the rules for naming the monatomic ions. 

If there is more than one monatomic cation of an element, Rule 1 is not sufficient. The Stock system of nomenclature names the cations after the element, as in Rule 1, but follows this by a Roman numeral in parentheses denoting the charge on the ion. Example Fe is called iron(II) ion and Fe is called iron(III) ion. ... 

Since the oxidation number of an atom in an element is always zero, Ca and O in O2 have oxidation numbers of zero. Another rule follows from the definition of oxidation number The oxidation number of an atom that exists in a substance as a monatomic ion equals the charge on that ion. So the oxidation number of Ca in CaO is -1-2 (the charge on Ca ), and the oxidation number of O in CaO is -2 (the charge... 

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