Chapter 4, Problem 3STP

Interpretation Introduction

Interpretation: The incorrect nomenclature for these compounds has to be identified.

Concept introduction: To name a compound, certain rules are followed. The given compounds are binary compounds.

Binary compounds are of three types:

• Type-I: Compound in which a metal forms ionic bond with a non-metal and the metal can form only one type of ions.
• Type-II: Compound in which a metal forms ionic bond with a non-metal and the metal can form more than one type of ions.
• Type-III: Compound in which a non-metal forms bond with a non-metal.

There is one another type of compound in which metal is bonded with a polyatomic ion

Rules for naming these compounds:

Type-I:

• Name of metal cation is written as name of element.
• Name of anion is written using root name and adding ‘ide’ to it.
• Writing these names in the same sequence gives the name of compound.

Type-II:

• Name of metal cation is written as name of element followed by charge carried by it in roman numerals in bracket.
• Name of anion is written using root name and adding ‘ide’ to it.
• Writing these names in the same sequence gives the name of compound.

Type-III:

• It is name by writing the name of first element as same as element.
• Second element in anionic form and prefixes are used to denote the number of atoms. Prefix mono is not used for first element.

When metal is bonded with polyatomic ion, rules are similar to ionic binary compounds.

Answer to Problem 3STP

Option D

Explanation of Solution

In nomenclature, cation names are placed always before anion name with their specific charge in brackets in roman numerals such as copper (II) oxide. To indicate the charge on counter ion, number is also indicated in prefix of the other ion. Example in ${\text{PCl}}_3$ , charge on $\text{P}$ is $+3$ so tri is prefixed to chloride ion.

So Option D is incorrect as all names from A-C are correct.

Conclusion

  $\text{P}$ can show multiple valencies that is $+3$ or $+5$ .So roman numeral is introduced after its name to specify its charge.

In ${\text{PCl}}_3$ element $\text{P}$ has $+3$ state so III is used in bracket hence correct name can be phosphorus (III) chloride or phosphorus trichloride.

Similarly, ${\text{MgCl}}_{\text{2}}$ is named as magnesium dichloride to show that $\text{Mg}$ has valency of $+2$ and 2 ${\text{Cl}}^{-}$ balance its charge.

In $\text{CuO}$ the element $\text{Cu}$ has $+2$ state so correct name is copper (II) oxide.