Question

Write the chemical formula for the following ternary compounds given their constituent ions: (a) strontium nitrite, \(\mathrm{Sr}^{2+}\) and \(\mathrm{NO}_{2}^{-}\) (b) zinc permanganate, \(\mathrm{Zn}^{2+}\) and \(\mathrm{MnO}_{4}\) - (c) calcium chromate, \(\mathrm{Ca}^{2+}\) and \(\mathrm{CrO}_{4}^{2-}\) (d) chromium(III) perchlorate, \(\mathrm{Cr}^{3+}\) and \(\mathrm{ClO}_{4}^{-}\)

Short answer

(a) \(\text{Sr(NO}_2\text{)}_2\), (b) \(\text{Zn(MnO}_4\text{)}_2\), (c) \(\text{CaCrO}_4\), (d) \(\text{Cr(ClO}_4\text{)}_3\)

Step-by-step solution

Identify Charges and Determine Formula for Strontium Nitrite

Strontium (Sr) has a charge of +2, and nitrite (NO₂) has a charge of -1. To balance the charges, we need two nitrite ions for each strontium ion. Therefore, the formula for strontium nitrite is \( \text{Sr(NO}_2\text{)}_2 \).

Identify Charges and Determine Formula for Zinc Permanganate

Zinc (Zn) has a charge of +2, and permanganate (MnO₄) has a charge of -1. To make the compound neutral, we need two permanganate ions for each zinc ion. Thus, the formula for zinc permanganate is \( \text{Zn(MnO}_4\text{)}_2 \).

Identify Charges and Determine Formula for Calcium Chromate

Calcium (Ca) has a charge of +2, and chromate (CrO₄) has a charge of -2. The charges are already balanced, so we only need one ion of each. The formula for calcium chromate is \( \text{CaCrO}_4 \).

Identify Charges and Determine Formula for Chromium(III) Perchlorate

Chromium (Cr) has a charge of +3, and perchlorate (ClO₄) has a charge of -1. To balance the charges, we need three perchlorate ions for each chromium ion. Therefore, the formula for chromium(III) perchlorate is \( \text{Cr(ClO}_4\text{)}_3 \).

Key concepts

Ternary Compounds

Ternary compounds are fascinating structures in chemistry composed of three different elements, typically involving a metal and two nonmetals. These compounds show us how elements can come together in more complex formations beyond binary compounds, which only have two elements. One of the most interesting aspects of ternary compounds is how they involve a polyatomic ion—a group of atoms that together carry a charge. For example, nitrite \( \mathrm{NO}_2^- \), present in strontium nitrite, is a polyatomic ion that partners with the metallic ion strontium \( \mathrm{Sr}^{2+} \), to form the ternary compound. These compounds are crucial to many practical applications, including industrial and biological processes, making them an essential topic of study in chemistry.

Ion Charges

Ion charges play a pivotal role in the formation of chemical compounds, guiding how atoms combine with one another. Ions can be either positively charged (cations) or negatively charged (anions). The charge results from an imbalance between protons and electrons in an atom or group of atoms. Understanding ion charges allows chemists to predict how different elements will react and bond.

• For instance, zinc \( \mathrm{Zn}^{2+} \) has a positive charge because it loses two electrons.
• Similarly, permanganate \( \mathrm{MnO}_4^- \) has a negative charge because it gains an extra electron.

The magnitude of the charges is crucial: metals often form fixed charges, like calcium \( \mathrm{Ca}^{2+} \), while many nonmetals can exhibit variable charges. Recognizing the charges helps in predicting the correct stoichiometry necessary to create balanced compounds.

Charge Balancing

To form stable chemical compounds, charge balancing is essential. This process involves ensuring that the total positive charges equal the total negative charges. Successfully achieving charge balance results in neutral compounds, which are the most stable form.
A step-by-step example can illustrate this:

• In strontium nitrite, we have \( \mathrm{Sr}^{2+} \) requiring two nitrite ions \( \mathrm{NO}_2^- \) to reach neutrality, like \( \mathrm{Sr(NO}_2\mathrm{)}_2 \).
• Zinc permanganate is similarly balanced by adding two permanganate ions \( \mathrm{MnO}_4^- \) to zinc \( \mathrm{Zn}^{2+} \), forming the compound \( \mathrm{Zn(MnO}_4\mathrm{)}_2 \).

By aligning charges correctly, chemists ensure the formation of stable and functional compounds.

Chemical Nomenclature

Chemical nomenclature is the systematic naming of chemical compounds to ensure clear communication in the scientific community. The IUPAC (International Union of Pure and Applied Chemistry) sets rules for naming compounds, making it essential to understand them for writing and recognizing formulas.
In ternary compounds:

• The metal is often listed first, followed by the polyatomic ion. For example, strontium nitrite becomes \( \text{Sr(NO}_2\text{)}_2 \).
• When dealing with transition metals, use Roman numerals to indicate the metal's oxidation state, such as chromium(III) perchlorate for \( \text{Cr(ClO}_4\text{)}_3 \).

Adhering to these naming conventions allows chemists and students to seamlessly understand and communicate chemical information, ensuring clarity and reducing errors.