Roman numerals, cations with

In contrast, we never use Roman numerals with compounds of the Group 1 or Group 2 metals they always form cations with charges of +1 or +2, respectively. 

The name of a monatomic cation is the same as the name of the element forming it, with the addition of the word ion, as in sodium ion for Na+. When an element can form more than one kind of cation, such as Cu+ and Cu2+ from copper, we use the oxidation number, the charge of the cation, written as a Roman numeral in parentheses following the name of the element. Thus, Cu+ is a copper(I) ion and Cu2+ is a copper(II) ion. Similarly, Fe2+ is an iron(II) ion and Fe3" is an iron(III) ion. As shown in Fig. C.6, most transition metals form more than one kind of ion so unless we are given other information we need to include the oxidation number in the names of their compounds. 

Name compounds by applying the guidelines. The guidelines for naming binary compounds that contain metals differ from those for compounds containing no metal. Unless a metal forms only one stable atomic cation, its charge must be specified with a Roman numeral in parentheses. 

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... 

A The name of each of these ionic compounds is the name of the cation followed by that of the anion. Each anion name is a modified (with the ending ide ) version of the name of the element. Each cation name is the name of the metal, with the oxidation state appended in Roman numerals in parentheses if there is more than one type of cation for that metal. 

A. SnF. The Roman numeral within parentheses tells you that you re dealing with Sn +. Because fluorine is a halogen, it always has a charge of -1 in ionic compounds, which means that four fluoride anions are necessary to cancel the four positive charges of a single tin cation. Therefore, the compound is SnF. ... 

Pb(S04)2 The cation lead is a metal with a variable charge, as indicated by the Roman numeral IV in parentheses. This classification means that lead has a charge of +A. SO is the polyatomic ion sulfate with a charge of -2. To balance out the charges, you need two sulfate ions for each lead ion. Thus, the formula has one Pb ion with a total charge of -1-4 and two sulfate ions with a total charge of -A. To indicate the need for two polyatomic ions, you put pcirentheses around the sulfate ion and write the 2 as a subscript outside the parentheses. 

The thing about transition metals is that the same transition metal can form cations with different charges. Differently charged metal cations need different names so chemists don t get any more confused than they already are. These days, you indicate these differences by using Roman numerals within parentheses to denote the positive charge of the metal ion. However, an older method adds the suffix -ous or -ic to indicate the cation with the smaller or larger charge, respectively. For example ... 

Metal cations team up with nonmetal anions to form ionic compounds. What s more, the ratio of cations to anions within each formula unit depends on the charge assumed by the fickle transition metal. The formula unit as a whole must be electrically neutral. The rules you follow to name an ionic compound must accommodate the whims of transition metals. The system of Roman numerals or suffixes applies in such situations ... 

If the transition metal forms only one cation, you name it like a representative metal cation name the element and call it a cation. If the transition metal forms more than one cation, you need to name the metal and then indicate the charge on the cation with Roman numerals in parentheses. 

Solution For the cation, find the symbol for cobalt (Co) and recognize that it is present as Co2+ ions from the Roman numerals. For the anion, remember the phosphite ion is PO33-. A neutral charge is achieved with 3 Co2+ ions for every 2 PO33- ions. Add eight FI2O for water of hydration for the answer ... 

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 binary nonmetal-nonmetal compounds are named with the prefixes the variable cations are named with the Roman numerals and the constant cations are named with neither (a) Carbon tetrachloride (b) Sodium carbonate... 

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. 

We will assume that all of the metallic elements other than those mentioned above can have more than one charge, so their cation names will include a Roman numeral. For example, Mn is named manganese(II). We know to put the Roman numeral in the name because manganese is not on our list of metals with only one charge. 

Before you can write a chemical formula from the name of a compound, you need to recognize what type of compound the name represents. For binary ionic compounds, the first part of the name is the name of a metallic cation. This may include a Roman numeral in parentheses. The anion name starts with the root of the name of a nonmetal and ends with -ide. 

Chemical formulas describe the simplest atom ratio (empirical formula), actual atom number (molecular formula), and atom arrangement (structural formula) of one unit of a compound. An ionic compound is named with cation first and anion second. For metals that can form more than one ion, the charge is shown with a Roman numeral. Oxoanions have suffixes, and sometimes prefixes, attached to the element root name to indicate the number of oxygen atoms. Names of hydrates give the number of associated water molecules with a numerical prefix. Acid names are based on anion names. Covalent compounds have the first word of the name for the element that is leftmost or lower down in the periodic table, and prefixes show the number of each atom. The molecular (or formula) mass of a compound is the sum of the atomic masses in the formula. Molecules are depicted by various types of formulas and models. 

Fig. 7.1 A separation of metal ions and mettaloid ions, As(lll) and Sb(lll), into three categories class A, borderline, and class B ions. The class B index X r is plotted for each ion against the class A index Z /r. In these expression is the metal-ion electronegativity, r its ionic radius, and Z its formal charge. Oxidation states given by Roman numerals imply that simple, hydrated cations do not exist even in acidic solutions. (Reprinted from Nieboer and Richardson (1980), Copyright 2002, with permission from Elsevier Science).

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