Question

Each of the following compounds is incorrectly named. What is wrong with each name, and what is the correct name for each compound? a. \(\mathrm{FeCl}_{3},\) iron chloride b. \(\mathrm{NO}_{2},\) nitrogen (IV) oxide c. CaO, calcium(Il) monoxide d. \(\mathrm{Al}_{2} \mathrm{S}_{3},\) dialuminum trisulfide e. \(\operatorname{Mg}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2},\) manganese diacetate f. \(\mathrm{FePO}_{4},\) iron(II) phosphide g. \(\mathrm{P}_{2} \mathrm{S}_{5}\) , phosphorus sulfide h. \(\mathrm{Na}_{2} \mathrm{O}_{2},\) sodium oxide i. \(\mathrm{HNO}_{3},\) nitrate acid j. \(\mathrm{H}_{2} \mathrm{S},\) sulfuric acid

Short answer

a. iron(III) chloride b. nitrogen(IV) oxide c. calcium oxide d. aluminum sulfide e. magnesium acetate f. iron(III) phosphate g. diphosphorus pentasulfide h. sodium peroxide i. nitric acid j. hydrosulfuric acid or hydrogen sulfide

Step-by-step solution

a. Correcting the name of \(\mathrm{FeCl}_{3}\)

Since \(\mathrm{FeCl}_{3}\) is an ionic compound, we need to identify the charge of the metal ion (iron) to name it correctly. Iron has a charge of 3+ in this compound, so the correct name is iron(III) chloride.

b. Correcting the name of \(\mathrm{NO}_{2}\)

The given name, nitrogen (IV) oxide, uses an incorrect oxidation state of nitrogen. The proper oxidation state in \(\mathrm{NO}_{2}\) is 4+. Therefore, the correct name is nitrogen(IV) oxide.

c. Correcting the name of CaO

The name "calcium(II) monoxide" has an unnecessary Roman numeral and a prefix for the oxygen. Since calcium forms only one type of compound, we drop the Roman numeral, and the correct name for this ionic compound is calcium oxide.

d. Correcting the name of \(\mathrm{Al}_{2} \mathrm{S}_{3}\)

For this ionic compound, the name "dialuminum trisulfide" incorrectly uses prefixes. The proper nomenclature for ionic compounds does not include prefixes. The correct name is aluminum sulfide.

e. Correcting the name of \(\operatorname{Mg}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\)

The given name is incorrect because it says "manganese" instead of "magnesium." The correct name for this ionic compound is magnesium acetate.

f. Correcting the name of \(\mathrm{FePO}_{4}\)

In the given name, "iron(II) phosphide," there is an incorrect Roman numeral and an incorrect suffix for the anion. For this ionic compound, the iron has a charge of 3+, so the correct name is iron(III) phosphate.

g. Correcting the name of \(\mathrm{P}_{2} \mathrm{S}_{5}\)

Since this is a molecular compound, we need to use prefixes to indicate the ratio of atoms in the compound. The correct name for \(\mathrm{P}_{2} \mathrm{S}_{5}\) is diphosphorus pentasulfide.

h. Correcting the name of \(\mathrm{Na}_{2} \mathrm{O}_{2}\)

The given name, sodium oxide, uses an incorrect formula for this compound. The correct formula is NaO, making the name sodium peroxide.

i. Correcting the name of \(\mathrm{HNO}_{3}\)

The given name, "nitrate acid," uses an incorrect prefix. Acids are named based on their anions, which in this case is the nitrate ion. The correct name is nitric acid.

j. Correcting the name of \(\mathrm{H}_{2} \mathrm{S}\)

The given name, "sulfuric acid," is incorrect. Acids are named based on their anions. For this compound, the anion is sulfide, so the correct name is hydrosulfuric acid or hydrogen sulfide.

Key concepts

Ionic Compounds

Ionic compounds are essential to understand in chemistry, as they consist of ions held together by strong electrostatic forces. These ions form a lattice structure, creating high melting and boiling points. A key feature of ionic compounds is their use of a metal and a non-metal; the metal donates an electron to become a positively charged cation, while the non-metal accepts an electron to become a negatively charged anion.

When naming ionic compounds, it is crucial to understand the charges of these ions. The metal ion's oxidation state should be specified using Roman numerals only when the metal can exhibit more than one oxidation state. For instance, in \( \text{FeCl}_3\), iron can have more than one oxidation state, thus requiring specification as iron(III) chloride. Importantly, do not use prefixes for ionic compounds, such as "di-" or "tri-", which are reserved for molecular compounds.

Molecular Compounds

Molecular compounds, also known as covalent compounds, are formed when two non-metal atoms share electrons to achieve a full valence shell, resulting in a molecule. The terminology for these compounds is crucially different from ionic compounds, particularly the use of prefixes.

For instance, the compound \(\text{P}_2\text{S}_5\) is named using prefixes to indicate the number of each atom, resulting in the name diphosphorus pentasulfide. Prefixes like "mono-", "di-", "tri-", "tetra-", are used extensively to clarify the number of atoms involved, emphasizing the covalent nature of molecule formation.

Oxidation States

Oxidation states, or oxidation numbers, indicate the number of electrons that an atom can gain, lose, or share during a chemical reaction. These numbers are essential for correctly naming and understanding the composition of compounds.

In ionic compounds, identifying the correct oxidation state is crucial. For example, \(\text{FePO}_4\) where iron can have different charges, needs its oxidation state specified as (III) instead of (II), leading to its correct name, iron(III) phosphate.

The oxidation state is essential for determining how compounds like \(\text{NO}_2\) are named. Even though it's a molecular compound, understanding that nitrogen typically involves an oxidation state of +4 in this context helps with the correct naming as nitrogen(IV) oxide.

Prefixes in Chemistry

Prefixes in chemistry serve as an important tool for indicating the number of atoms of each element in a compound, specifically in molecular compounds.

For molecular compounds, prefixes such as "mono-", "di-", "tri-", ", "tetra-", "penta-" etc., provide clarity about the elemental composition. They are integral in the nomenclature to avoid misunderstanding, as illustrated by \(\text{P}_2\text{S}_5\), which is named diphosphorus pentasulfide to correctly identify 2 phosphorus atoms and 5 sulfur atoms.

However, in the case of ionic compounds, prefixes are not used. Instead, these rely on Roman numerals when necessary to convey the oxidation state of transition metals, to convey the specifics of the ionic bonding and composition.