3.10: Ionic Bonding: Writing Chemical Names of Ionic Compounds Containing Transition Metals (2024)

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Naming Ionic Compounds Containing Transition Metals

The chemical name of an ionic compound is based solely on the identities of the ions that it contains.Specifically, the names of the ions are modified by removing the word "ion" from each, and the remaining terms are written inthe order in which theyappear in the corresponding ionic chemical formula. Since the subscripts in an ionic chemical formula are the result of achieving charge-balance between the compound's constituent ions, referencing subscripts in an ionic chemical name is redundant. Therefore, ionic compoundsdo notinclude any numerical prefixes.

For example, considerSn₃P₄, which is thechemical formula for an ionic compound that isformed when phosphorus and tin bond with one another.

These elements bond with one another as ions, not as neutral atoms. Therefore,more accurately,Sn₃P₄is thechemical formula for the ionic compound that is formed when the phosphide ion, P^–3, the anion formed upon the ionization of phosphorus, and atin ionbond with one another. Recall that the suffixof an anionis "-ide," as a verbal indicator of its negative charge. However, tin, Sn, is able to achieve a stable electron configuration through multiple ionization pathways and couldionize to form either Sn⁺²or Sn⁺⁴. Therefore, the specific charge of the transition metal cation must be definitively established before an unambiguous ionic chemical name can be written.

An adaptation ofthe "Criss-Cross Method," which wasutilized to determine the subscripts in ionic chemical formulas, can be used for this task. However, asthe subscripts in ionic chemical formulas are a lowest-common ratio of whole numbers, the charges found by employing a "reverse version" of this "shortcut" procedurecan be incorrect. Therefore, the "Reverse Criss-Cross Method" will not be discussed further in this section.

In contrast, the alternative process, the "Ratio Method," can be reliably modified and employed to determine the charge of a transition metal cation. Recall that this processestablishes a cation-to-anion ratio by equating the total charges of thecationsin an ionic compound to the sum of the charges ofthe anions in that compound, in order to ensure that the final compound is a net-neutral species. As the "Reverse Ratio Method"requires the use of arelative cation-to-anion ratio,using subscripts that have been reduced to a lowest-common ratio of whole numbers will still consistently indicate the correct charge of a transition metal cation. In this procedure, a mini-equation, in which the subscripton the cationis multiplied by a variable, such as x, and the subscripton the anionis multiplied by theabsolute valueof its charge, is solved. Note that the charge of theanionis always a known quantity, as all anions are derived from main group elements, which have defined, predictable charges. Additionally,theabsolute valueof the anionchargeis used, asanions are negative, and this procedure is being employed to find the charge of a cation, which is positive. Finally, an absolute value is represented by writing a quantity inside oftwo vertical bars. When solving equations that involve absolute values, a positive value is applied in subsequent mathematical operations.

See Also

2.7: Ions and Ionic Compounds

In the current example, the subscripton the cation, tin(Sn), is "3," and thesubscripton the phosphide anion(P^–3), which has a known charge of–3,is "4." Therefore,

3(x) =4(|–3|)
3(x) =4(3)
x=4

This result indicates that thetin cationin this example has a charge of+4and, therefore, is symbolized asSn⁺⁴.

After establishing the correct charge of the transition metal cation, the appropriateRoman numeral can be incorporated into itsion name. Recall that Roman numerals should be writtenin parentheses after the element name, but before the word "ion." Based on the results of the "Reverse Ratio Method," thistin cationhas a charge of+4, which is represented by a Roman numeral(IV)in an ion name. Therefore, the unambiguous nameof"Sn⁺⁴"is thetin (IV) ion.

When naming an ionic compound, the word "ion" is removed from both the cation and the anion terms, as no charges are explicitly-written in an ionic chemical formula. Each constituent particle, such asP^–3 andSn⁺⁴, is charged and, consequently, has a namethat includes the word "ion." However, an ionic compound, such asSn₃P₄,is a net-neutral species, due to the charge-balance achieved between these particles.Therefore, the term "ion" should not be incorporated into the chemical name of an ionic compound. In this example,"phosphide ion" is shortened to "phosphide," and "tin (IV) ion" becomes "tin (IV)."

Finally, since the cationis symbolized before the anion in anionic chemical formula, the cation term appears first in the chemical name of an ionic compound. Therefore, in this example, the phrase "tin (IV)" is written before "phosphide." As the subscripts in an ionic chemical formula are not referenced in an ionic chemical name, the result ofcombining these terms,"tin (IV)phosphide," is the chemically-correct name for Sn₃P₄.

Example \(\PageIndex{1}\)

Write the chemical name of NiI₃, an ionic compound that is formed when nickeland iodine bond with one another.

Solution

Moreaccurately,NiI₃is thechemical formula for the ionic compound that is formed when anickel ionand the iodide ion (I^–1, the anion formed upon the ionization of iodine) bond with one another. However, nickel(Ni)is able to achieve a stable electron configuration through multiple ionization pathways and couldionize to form either Ni⁺²or Ni⁺³. Therefore, the specific charge of the transition metal cation must be definitively established before an unambiguous ionic chemical name can be written.

In the "Reverse Ratio Method," a mini-equation, in which the subscripton the cationis multiplied by a variable, such as x, and the subscripton the anionis multiplied by theabsolute valueof its charge, is solved. Note that the charge of theanionis always a known quantity, as all anions are derived from main group elements, which have defined, predictable charges. Additionally,theabsolute valueof the anionchargeis used, asanions are negative, and this procedure is being employed to find the charge of a cation, which is positive. Finally, an absolute value is represented by writing a quantity inside oftwo vertical bars. When solving equations that involve absolute values, a positive value is applied in subsequent mathematical operations.

In the current example, thesubscripton the cation, nickel(Ni), is an unwritten "1," and thesubscripton the iodide anion(I^–1), which has a known charge of–1,is "3." Therefore,

1(x) =3(|–1|)
1(x) =3(1)
x=3

This result indicates that thenickel cationin this example has a charge of+3and, therefore, is symbolized asNi⁺³.

After establishing the correct charge of the transition metal cation, the appropriateRoman numeral can be incorporated into itsion name. Recall that Roman numerals should be writtenin parentheses after the element name, but before the word "ion." Based on the results of the "Reverse Ratio Method," thisnickel cationhas a charge of+3, which is represented by a Roman numeral(III)in an ion name. Therefore, the unambiguous nameof"Ni⁺³"is thenickel (III) ion.

When naming an ionic compound, the word "ion" is removed from both the cation and the anion terms, as no charges are explicitly-written in an ionic chemical formula. As a result,"iodide ion" is shortened to "iodide," and "

nickel (III)ion" becomes "nickel (III)."Finally, since the cationis symbolized before the anion in anionic chemical formula, the cation term appears first in the chemical name of an ionic compound. Therefore, in this example, the phrase "nickel (III)" is written before "iodide." As the subscripts in an ionic chemical formula are not referenced in an ionic chemical name, the result ofcombining these terms,"nickel (III)iodide," is the chemically-correct name for NiI₃.

Exercise \(\PageIndex{1}\)

Write the chemical name that corresponds to each of the following chemical formulas.

PbO, an ionic compound that is formed when lead and oxygen bond with one another.
Cu₃N, an ionic compound that is formed when nitrogen and copper bond with one another.

Answer a

Moreaccurately,PbOis thechemical formula for the ionic compound that is formed when alead ionand the oxide ion (O^–2, the anion formed upon the ionization of oxygen) bond with one another. However, lead(Pb)is able to achieve a stable electron configuration through multiple ionization pathways and couldionize to form either Pb⁺²or Pb⁺⁴. Therefore, the specific charge of the transition metal cation must be definitively established before an unambiguous ionic chemical name can be written.

In the "Reverse Ratio Method," a mini-equation, in which the subscripton the cationis multiplied by a variable, such as x, and the subscripton the

anionis multiplied by theabsolute valueof its charge, is solved. Note that the charge of theanionis always a known quantity, as all anions are derived from main group elements, which have defined, predictable charges. Additionally,theabsolute valueof the anionchargeis used, asanions are negative, and this procedure is being employed to find the charge of a cation, which is positive. Finally, an absolute value is represented by writing a quantity inside oftwo vertical bars. When solving equations that involve absolute values, a positive value is applied in subsequent mathematical operations.

In the current example, the subscriptson both the cation, lead(

Pb), and on theoxide anion(O^–2),which has a known charge of–2, areunwritten "1"s. Therefore,

1(x) =1(|–2|)
1(x) =1(2)
x=2

This result indicates that thelead cationin this example has a charge of+2and, therefore, is symbolized asPb⁺².

After establishing the correct charge of the transition metal cation, the appropriateRoman numeral can be incorporated into itsion name. Recall that Roman numerals should be writtenin parentheses after the element name, but before the word "ion." Based on the results of the "Reverse Ratio Method," thislead cationhas a charge of+2, which is represented by a Roman numeral(II)in an ion name. Therefore, the unambiguous nameof"Pb⁺²"is the

lead (II) ion.

When naming an ionic compound, the word "ion" is removed from both the cation and the anion terms, as no charges are explicitly-written in an ionic chemical formula. As a result,"oxide ion" is shortened to "oxide," and "

lead (II)ion" becomes "lead (II)."Finally, since the cationis symbolized before the anion in anionic chemical formula, the cation term appears first in the chemical name of an ionic compound. Therefore, in this example, the phrase "lead (II)" is written before "oxide." As the subscripts in an ionic chemical formula are not referenced in an ionic chemical name, the result ofcombining these terms,"lead (II)oxide," is the chemically-correct name for PbO.

Answer b

Moreaccurately,Cu₃Nis thechemical formula for the ionic compound that is formed when the nitride ion (N^–3) andacopper ionbond with one another. However, copper(Cu)is able to achieve a stable electron configuration through multiple ionization pathways and couldionize to form either Cu⁺¹or Cu⁺². Therefore, the specific charge of the transition metal cation must be definitively established before an unambiguous ionic chemical name can be written.

In the "Reverse Ratio Method," a mini-equation, in which the subscripton the cationis multiplied by a variable, such as x, and the subscripton the

anionis multiplied by theabsolute valueof its charge, is solved.In the current example, the subscripton the cation, copper(Cu), is "3," and thesubscripton the nitride anion(N^–3), which has a known charge of–3,is an unwritten "1." Therefore,

3(x) =1(|–3|)
3(x) =1(3)
x=1

This result indicates that thecopper cationin this example has a charge of+1, which is represented by a Roman numeral(I)in an ion name.Therefore, the unambiguous nameofthecopper cationin this example, "Cu⁺¹,"is thecopper (I) ion.

When naming an ionic compound, the word "ion" is removed from both the cation and the anion terms, as no charges are explicitly-written in an ionic chemical formula. As a result,"nitride ion" is shortened to "nitride," and "

copper (I)ion" becomes "copper (I)."Finally, the cation term appears first in the chemical name of an ionic compound, sothe phrase "copper (I)" is written before "nitride." As the subscripts in an ionic chemical formula are not referenced in an ionic chemical name, the result ofcombining these terms,"copper (I)nitride," is the chemically-correct name for Cu₃N.