Problem 82 - Chemistry Matter and Change

Question

Name each of the following ionic compounds. $$ \begin{array}{l}{\text { a. } \mathrm{K}_{2} \mathrm{O}} \\ {\text { b. } \mathrm{CaCl}_{2}} \\ {\text { c. } \mathrm{Mg}_{3} \mathrm{N}_{2}} \\\ {\text { d. } \mathrm{NaClO}_{2}} \\ {\text { e. } \mathrm{KNO}_{3}}\end{array} $$

Step-by-Step Solution

Answer

a. Potassium oxide b. Calcium chloride c. Magnesium nitride d. Sodium chlorite e. Potassium nitrate

Step 1: Potassium oxide

Identify the cation and anion in the compound \( ext{K}_2 ext{O}\). The cation is potassium (K) and the anion is oxide (O). Combine their names to name the compound as 'potassium oxide'.

Step 2: Calcium chloride

For \( ext{CaCl}_2\), the cation is calcium (Ca) and the anion derived from chlorine is chloride (Cl). Therefore, the name of the compound is 'calcium chloride'.

Step 3: Magnesium nitride

Identify the cation and anion in the compound \( ext{Mg}_3 ext{N}_2\). The cation is magnesium (Mg) and the anion derived from nitrogen is nitride (N). Thus, the compound is named 'magnesium nitride'.

Step 4: Sodium chlorite

In \( ext{NaClO}_2\), the cation is sodium (Na) and the anion is chlorite (\( ext{ClO}_2^-\)). Combine their names to name the compound as 'sodium chlorite'.

Step 5: Potassium nitrate

For \( ext{KNO}_3\), the cation is potassium (K) and the anion is nitrate (\( ext{NO}_3^-\)). Hence, the name of the compound is 'potassium nitrate'.

Key Concepts

Cation Identification

Cations are positively charged ions formed when an atom loses electrons. In ionic compounds, cations are typically metal ions. For example, in the exercise you're looking at, potassium (\( \text{K} \) ) and calcium (\( \text{Ca} \) ) are examples of cations. Identifying the cation in a compound is crucial because it usually appears first in the chemical formula.

To identify the cation, look for the metal or positively charged polyatomic ion in the formula:

• For example, in \( \text{K}_2\text{O} \), potassium (K) is the cation.
• In \( \text{CaCl}_2 \), calcium (Ca) is the cation.

Recognizing the cation involves checking the periodic table to see which element appears first or is most metallic, thus generally carrying a positive charge. This step is essential before moving on to naming the entire compound.

Anion Identification

Anions are negatively charged ions, formed when an atom gains extra electrons. In any given chemical compound, the anion is most often a non-metal ion or a polyatomic ion that follows the cation in the formula. For instance, in the formula \( \text{K}_2\text{O} \), the oxygen (O) acts as an anion.

To identify the anion:

• Find the non-metal element or polyatomic ion in the formula.
• Examples are oxide (\( \text{O}^{2-} \)) in \( \text{K}_2\text{O} \) and chloride (\( \text{Cl}^- \)) in \( \text{CaCl}_2 \).
• In polyatomic forms like chlorite (\( \text{ClO}_2^- \)) in \( \text{NaClO}_2 \), identify complex ions instead of single elements.

Anion identification is the second step after recognizing the cation and sets the stage for proper naming of the compound by adding the correct suffix if applicable.

Chemical Formulas

Chemical formulas are concise ways to represent chemical substances using symbols and numbers. They tell you the types and ratios of atoms within a compound. For ionic compounds, formulas display the balance between cations and anions, ensuring neutrality of charge.

Understanding chemical formulas involves:

• Identifying the ratio of cations to anions. For example, \( \text{K}_2\text{O} \) suggests two potassium ions for each oxide ion.
• Recognizing the charges: Potassium is +1, so two are needed to balance one oxide ion which typically has a charge of -2.

Accurate writing and interpretation of chemical formulas are foundational in naming compounds and understanding chemical reactions.

Compound Naming

Naming ionic compounds correctly involves combining the names of the cation and anion in a clear sequence. The name starts with the cation, followed by the anion. The anion often has an "-ide" suffix if it's a single element, or carries the name of the polyatomic ion if it's more complex.

When naming compounds:

• For simple binary compounds like \( \text{CaCl}_2 \), reformulate it as calcium chloride, with the cation name first.
• In cases involving polyatomic ions, like \( \text{NaClO}_2 \), name it sodium chlorite, including the full name of the polyatomic ion.
• Remember: no prefixes like "mono-" or "di-" are used in ionic compound names even if they appear in the formula.

With practice, you'll swiftly recognize patterns in naming, facilitating deeper comprehension and accurate communication in chemistry.