Question

Name each of the following oxides. Assuming that the compounds are ionic, what charge is associated with the metallic element in each case? (a) NiO, (b) \(\mathrm{MnO}_{2}\) (c) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{MoO}_{3}\).

Short answer

(a) NiO is named Nickel(II) oxide, and the charge associated with nickel is +2. (b) \(\mathrm{MnO}_{2}\) is named Manganese(IV) oxide, and the charge associated with manganese is +4. (c) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) is named Chromium(III) oxide, and the charge associated with each chromium ion is +3. (d) \(\mathrm{MoO}_{3}\) is named Molybdenum(VI) oxide, and the charge associated with molybdenum is +6.

Step-by-step solution

(a) Naming NiO and finding the charge of Ni

In the compound NiO, we have nickel (Ni) and oxygen (O). The oxide ion has a -2 charge. In order to maintain a neutral compound, the nickel ion has to have a positive charge of +2. Therefore, the name of the compound is Nickel(II) oxide, and the charge associated with nickel is +2.

(b) Naming \(\mathrm{MnO}_{2}\) and finding the charge of Mn

In the compound \(\mathrm{MnO}_{2}\), we have manganese (Mn) and two oxygen ions, each with a -2 charge. The total charge of the oxygen ions is -4. To maintain a neutral compound, the manganese ion must have a positive charge of +4. Therefore, the name of the compound is Manganese(IV) oxide, and the charge associated with manganese is +4.

(c) Naming \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) and finding the charge of Cr

In the compound \(\mathrm{Cr}_{2} \mathrm{O}_{3}\), we have two chromium (Cr) and three oxygen ions, the latter with a total charge of -6. For the compound to be neutral, the two chromium ions must have a total positive charge of +6. Therefore, each chromium ion has a charge of +3. The name of the compound is Chromium(III) oxide, and the charge associated with each chromium ion is +3.

(d) Naming \(\mathrm{MoO}_{3}\) and finding the charge of Mo

In the compound \(\mathrm{MoO}_{3}\), we have molybdenum (Mo) and three oxygen ions, the latter with a total charge of -6. To maintain a neutral compound, the single molybdenum ion must have a positive charge of +6. Therefore, the name of the compound is Molybdenum(VI) oxide, and the charge associated with molybdenum is +6.

Key concepts

Oxidation States

Understanding oxidation states is key to determining the charge of atoms in ionic compounds. An oxidation state is a hypothetical charge that an atom would have if all bonds were ionic. It helps to determine how electrons are distributed among atoms in a compound. This concept is crucial when naming ionic compounds.
In ionic compounds, nonmetals often have known oxidation states. For instance, oxygen typically has an oxidation state of -2. By knowing this, you can deduce the oxidation state of the metal in a compound by ensuring that the total charge combines to zero.
For instance, in NiO, oxygen has an oxidation state of -2, meaning nickel must be +2 to counterbalance. Understanding this helps with the naming and understanding of ionic structures.

Naming Compounds

Naming ionic compounds correctly is a vital skill in chemistry. The name gives insight into the compound's composition and the oxidation states of its elements. In ionic compounds, the metal name appears first, followed by the nonmetal with an "-ide" suffix.
For transition metals, which can have multiple oxidation states, it's important to specify the oxidation state in roman numerals within parentheses. For example, "Nickel(II) oxide" indicates nickel's oxidation state is +2. This keeps compounds with similar compositions distinct.

• NiO - Nickel(II) oxide
• MnO₂ - Manganese(IV) oxide
• Cr₂O₃ - Chromium(III) oxide
• MoO₃ - Molybdenum(VI) oxide

Chemical Formulas

Understanding chemical formulas is necessary for comprehending the basics of ionic compounds. A chemical formula indicates the number and type of atoms present in a compound. The subscript numbers in chemical formulas show how many atoms or ions of each element are in one formula unit of the compound.
For example, in \({\rm{MnO}}_2\), the subscript '2' next to oxygen indicates two oxygen atoms in the compound. Similarly, \({\rm{Cr}}_2 {\rm{O}}_3\) reveals there are two chromium atoms for every three oxygen atoms.
Each formula leads to a different calculation of the oxidation states to maintain electrically neutral compounds. A correct understanding of the chemical formula aids in balancing equations and accurately naming compounds. This foundational knowledge builds towards more advanced chemistry topics.