Transition metals Roman numerals

There is one complication. As mentioned earlier, certain metals in the transition and post-transition series form more than one cation, for example, Fe2+ and Fe3+. To distinguish between these cations, the charge must be indicated in the name. This is done by putting the charge as a Roman numeral in parentheses after the name of the metal ... 

In naming the compounds of transition or post-transition metals, we ordinarily indicate the charge of the metal cation by a Roman numeral ... 

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. 

Step 1 Identify the cation and the anion (see Table D.l or Appendix 3A, if necessary). To determine the oxidation number of the cation, decide what cation charge is required to cancel the total negative charge of the anions. Step 2 Name the cation. If the metal can have more than one oxidation number (most transition metals and some metals in Groups 12 through 15/V), give its charge as a Roman numeral. 

Cr03 As a transition metal, chromium forms more than one stable cation. Name the metal first, using a Roman numeral to designate chromium s charge. Each of the three oxide anions has a -2 charge. To maintain net charge neutrality, Cr must be +6, so the name of the compound is chromium(VI) oxide. 

To avoid the necessity of memorizing a separate name for each ion, we can use the Stock system. In the Stock system, the charge of the cation appears as a Roman numeral immediately after the name of the element. Using the Stock system, we write Fe2+ as the iron(II) ion, and Cu+ as the copper(I) ion. Other than the necessity of indicating the charges, there are no differences between the naming of transition metal compounds and other compounds of the metals. So while KC1 is potassium chloride, CuCl is copper(I) chloride. 

Many transition metals and the group of six elements centered around lead on the periodic table commonly have more than one valence. The valence of these metals in a compound must be known before the compound can be named. Modern nomenclature rules indicate the valence of one of these metals with a Roman numeral suffix (Stock notation). Older nomenclature rules used different suffixes to indicate the charge. Examples ... 

The Roman numeral suffix is part of the name of the metal. Thus iron(III) is one word. Stock notation should be used for all metals that have a variable valence. This includes almost all the transition elements and the elements immediately around lead on the periodic table. Stock notation is often omitted for Zn, Cd, and Ag, as they do not have variable valence. The valences of some common metals and acids are listed in Appendix C. 

Use Roman numerals only for Group B transition metals whose charge you don t know. Don t use Roman numerals if you know the charge of the metallic cation, including alkali metals such as lithium (Li" ) and sodium (Na+) as well as alkaline earth metals such as calcium (Ca +) and magnesium (Mg +). 

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 ... 

For transition metal compounds, the charge on the cation is indicated by the Roman numeral in the name. Knowing the number of positive charges, you can then figure out the number of necessary negative charges for the associated anions. 

Lithium (group 1A) forms only the Li+ ion and does not need a Roman numeral. Potassium (group 1A) forms only the K+ ion. The carbonate ion has a —2 charge, so copper must be +2. A Roman numeral is needed because copper, a transition metal, can form more than one ion. 

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. 

Transition elements form ions with more than one charge, i.e. they have ions of different charges nd that is indicated as a Roman numeral in paranthesis next to the metal, e.g Fe (I) etc. 

Many of the common metals are transition elements that have more than one possible valence. For example, tin is able to form the ions Sn2+ and Sn4+, iron can form Fe2+ and Fe3+, and copper can form Cu+ and Cu2+. (The most common transition metals with more than one valence number are listed in Table 3.3.) The name of a compound must identify which ion is present in the compound. To do this, the element s name is used, followed by the valence in parentheses, written in Roman numerals. Therefore, Sn4+ is tin(IV), Fe3+ is iron(III), and Cu2+ is copper(II). This naming method is called the Stock system after Alfred Stock, a German chemist who first used it. Some examples of Stock system names are listed in Table 3.6. 

Note that the use of a Roman numeral in a systematic name is required only in cases in which more than one ionic compound forms between a given pair of elements. This case most commonly occurs for compounds containing transition metals, which often form more than one cation. Elements that form only one cation do not need to be identified by a Roman numeral. Common metals that do not require Roman numerals are the Group 1A elements, which form only 1+ ions the Group 2A elements, which form only 2+ ions and aluminum, which forms only Al3+. Common transition metals that do not require a Roman numeral (because they form only one ion) are zinc (Zn2+) and silver (Ag+). 

Cobalt is a transition metal that requires a Roman numeral. The two Br ions must be balanced by a Co2+ cation. 

Group lA and group 2A metals have only one oxidation number. Transition metals and metals on the right side of the periodic table often have more than one oxidation number. To distinguish between multiple oxidation numbers of the same element, the name of the chemical formula must indicate the oxidation number of the cation. The oxidation number is written as a Roman numeral in parentheses after the name of the cation. For example, the compound formed from Fe + and has the formula FeO and is named iron(II) oxide. The compound formed from Fe + and has the formula Fe203 and is named iron(III) oxide. 

The preceding method is sufficient for naming binary ionic compounds containing metals that exhibit only one oxidation number other than zero (Section 4-4). Most transition metals and the metals of Groups IIIA (except Al), IVA, and VA, exhibit more than one oxidation number. These metals may form two or more binary compounds with the same nonmetal. Ta distinguish among all the possibilities, the oxidation number of the metal is indicated by a Roman numeral in parentheses following its name. This method can be applied to any binary compound of a metal and a nonmetal. 

Many metals (usually transition metals) may form cations of more than one charge. In this case, a Roman numeral in parenthesis after the name of the element is used to indicate the ion s charge in a particular compound. This Roman numeral method is known as the Stock system. An older nomenclature used the suffix -ous for the lower charge and -ic for the higher charge and is still used occasionally. 

Compounds with Metals That Can Form More Than One Ion Many metals, particularly the transition elements (B groups), can form more than one ion, each with its own particular charge. Table 2.4 (on the next page) lists some examples, and Figure 2.16 shows their placement in the periodic table. Names of compounds containing these elements include a Roman numeral within parentheses immediately after the metal ion s name to indicate its ionic charge. For example, iron can form Fe " and Fe ions. The two compounds that iron forms with... 

The use of a Roman numeral in a systematic name for a compound is required only when more than one ionic compound forms between a given pair of elements. This occurs most often for compounds that contain transition metals, which frequently form more than one cation. 

Sometimes transition metals form only one ion, such as silver, which forms Ag zinc, which forms Zn and cadmium, which forms Cd. In these cases, chemists do not use a Roman numeral, although it is not "wrong" to do so. 

Certain transition metals form only one ion. Common examples are zinc (forms only Zn " ") and silver (forms only Ag ). For these cases the Roman numeral is omitted from the name. 

Contains Zn " " and PO Zn is a transition metal and may require a Roman numeral. However, because Zn forms only the Zn " " cation, the 11 is left out. Thus the name of the compound is given as zinc phosphate. 

Note that mercury(l) ions always occur bound together to form Flg2 ions. Although these are transition metals, they form only one type of ion, and a Roman numeral is not used. 

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