Question

Name the following substances: (a) \(\mathrm{Fe}(\mathrm{OH})_{2}\) (b) \(\mathrm{KMnO}_{4}\) (c) \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) (d) \(\mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)

Short answer

(a) Iron(II) hydroxide, (b) Potassium permanganate, (c) Sodium chromate, (d) Barium phosphate.

Step-by-step solution

Identify the Cation and Anion

For each chemical formula, identify the cation (positive ion) and the anion (negative ion). This will help us in determining the name of the compound by first naming the cation followed by the anion.

Name the Cation

(a) - Fe in \(\mathrm{Fe(OH)}_{2}\) is iron, which can have more than one charge. Here it forms Fe²⁺ (ferrous).(b) - K in \(\mathrm{KMnO}_{4}\) is potassium.(c) - Na in \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) is sodium.(d) - Ba in \(\mathrm{Ba}_{3}(\mathrm{PO}_{4})_{2}\) is barium.

Name the Anion

(a) - OH in \(\mathrm{Fe(OH)}_{2}\) is the hydroxide ion.(b) - MnO₄⁻ in \(\mathrm{KMnO}_{4}\) is the permanganate ion.(c) - CrO₄²⁻ in \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\) is the chromate ion.(d) - PO₄³⁻ in \(\mathrm{Ba}_{3}(\mathrm{PO}_{4})_{2}\) is the phosphate ion.

Combine the Names

(a) Combine the cation and anion names for \(\mathrm{Fe(OH)}_{2}\): ferrous hydroxide or iron(II) hydroxide.(b) Combine the cation and anion names for \(\mathrm{KMnO}_{4}\): potassium permanganate.(c) Combine the cation and anion names for \(\mathrm{Na}_{2} \mathrm{CrO}_{4}\): sodium chromate.(d) Combine the cation and anion names for \(\mathrm{Ba}_{3}(\mathrm{PO}_{4})_{2}\): barium phosphate.

Key concepts

Cation identification

Understanding cations is a fundamental aspect of chemical nomenclature. Cations are positively charged ions formed when an atom loses one or more electrons. Identifying them is the first step in naming an ionic compound. In the chemical formulas provided, the cations are the species that come first. For example, in \( \mathrm{Fe(OH)}_2 \), our cation is iron (Fe). Similarly, for \( \mathrm{KMnO}_4 \), \( \mathrm{K} \) represents the potassium cation. For \( \mathrm{Na}_2\mathrm{CrO}_4 \), the sodium cation is identified by \( \mathrm{Na} \), and in \( \mathrm{Ba}_3\mathrm{(PO}_4)_2 \), \( \mathrm{Ba} \) indicates barium cations. By identifying these positive ions, we set the stage for proper naming of the entire compound.

Anion identification

Anions are negatively charged ions, formed by the gain of electrons by an atom. Identifying anions is equally essential in ionic compound naming as identifying cations. In the chemical formulas at hand, the anion follows the cation. For instance, \( \mathrm{OH}^- \) is the hydroxide anion in \( \mathrm{Fe(OH)}_2 \). In \( \mathrm{KMnO}_4 \), \( \mathrm{MnO}_4^- \) is the permanganate anion. Similarly, \( \mathrm{CrO}_4^{2-} \) is the chromate anion in \( \mathrm{Na}_2 \mathrm{CrO}_4 \), while \( \mathrm{PO}_4^{3-} \) is the phosphate anion in \( \mathrm{Ba}_3(\mathrm{PO}_4)_2 \). Recognizing these negative ions is crucial to constructing the correct name of the compound.

Ionic compound naming

The process of naming ionic compounds involves combining the names of the identified cation and anion. Once we know both ions, we name the cation first, followed by the anion.

• For \( \mathrm{Fe(OH)}_2 \), we combine iron (Fe) and hydroxide (OH) to name it iron(II) hydroxide or ferrous hydroxide.
• Similarly, \( \mathrm{KMnO}_4 \) is named by combining potassium (K) and permanganate (MnO₄⁻) to form potassium permanganate.
• For \( \mathrm{Na}_2 \mathrm{CrO}_4 \), the name is sodium chromate, derived from sodium (Na) and chromate (CrO₄²⁻).
• Lastly, \( \mathrm{Ba}_3(\mathrm{PO}_4)_2 \) is named barium phosphate, from barium (Ba) and phosphate (PO₄³⁻).

Understanding how to systematically name these compounds simplifies recognizing chemical substances and their compositions.

Transition metals oxidation states

Transition metals are unique in having multiple oxidation states, which can lead to different charges and, therefore, different compound names. For instance, iron (Fe) can exist in multiple states, such as \( \mathrm{Fe}^{2+} \) and \( \mathrm{Fe}^{3+} \). When naming compounds with transition metals, it's important to indicate the specific oxidation state to avoid confusion.
In \( \mathrm{Fe(OH)}_2 \), iron is in the +2 oxidation state, which is indicated in the name iron(II) hydroxide. This distinguishes it from iron(III) hydroxide, which would be \( \mathrm{Fe(OH)}_3 \).
Keeping track of these oxidation states ensures precise communication in the naming of ionic compounds involving transition metals.