Problem 111 - Chemistry Matter and Change

Question

Name each ionic compound. a. \(\mathrm{CaO}\) b. BaS c. AlPO \(_{4}\) d. \(\operatorname{Ba}(\mathrm{OH})_{2}\) e. \(\operatorname{Sr}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

a. Calcium Oxide; b. Barium Sulfide; c. Aluminum Phosphate; d. Barium Hydroxide; e. Strontium Nitrate.

Step 1: Identify the cation and anion in the compound

For each chemical formula, first identify the cation (the positively charged ion) and the anion (the negatively charged ion). For example, in \(\text{CaO}\), \(\text{Ca}^{2+}\) is the cation and \(\text{O}^{2-}\) is the anion.

Step 2: Name the cation

The name of the cation is usually the same as the name of the element if it's a metal from the main groups (e.g., Calcium for \(\text{Ca}^{2+}\), Barium for \(\text{Ba}^{2+}\), etc.). Transition metals may require a Roman numeral indicating their charge.

Step 3: Name the anion

The anion name is typically derived from the element name but ends in '-ide' if it's a simple ion (e.g., Oxide for \(\text{O}^{2-}\), Sulfide for \(\text{S}^{2-}\)). For polyatomic ions, use the standard name like phosphate for \(\text{PO}_4^{3-}\).

Step 4: Combine the names to form the compound name

Write the name of the compound by stating the cation name followed by the anion name. For example, \(\text{CaO}\) becomes Calcium Oxide, and \(\text{BaS}\) becomes Barium Sulfide.

Step 5: Special naming for compounds with polyatomic ions

Some ions are polyatomic (e.g., \(\text{OH}^-\) is hydroxide, \(\text{NO}_3^-\) is nitrate). When naming compounds like \(\text{Ba(OH)}_2\), use the cation name first, followed by the polyatomic ion name to form Barium Hydroxide.

Key Concepts

Cation Identification

To understand and accurately name ionic compounds, it is crucial to first identify the cation in the chemical formula. The cation is the positively charged ion in a compound. It is typically represented by a metal element that has lost electrons, resulting in a positive charge. For instance, in

• \text{CaO}\ , Calcium (Ca) loses two electrons to become \( \text{Ca}^{2+} \).

Recognizing the cation involves looking at the metal part of the compound. These are usually located at the beginning of the chemical formula. Cations include:

• Sodium (Na⁺)
• Calcium (Ca²⁺)
• Barium (Ba²⁺)

Identifying the cation correctly is your first step in naming the compound.

Anion Identification

Equally important as identifying the cation is recognizing the anion, which is the negatively charged ion in an ionic compound. Non-metals usually form anions by gaining electrons. For example, in calcium oxide, oxygen (

• \text{O}^{2-}\ ) is the anion.

Anions can be:

• Derived from single elements, known as monatomic ions, like \( \text{Cl}^- \).
• Polyatomic, consisting of several atoms, like \( \text{NO}_3^- \), known as nitrate.

Once the correct anion is identified, its name is crafted from the element name ending in "-ide" for monatomic anions, such as chloride from chlorine.

Polyatomic Ions

In some ionic compounds, you will encounter polyatomic ions - ions composed of multiple atoms. These are considered a singular charged entity, often making the identification a bit tricky at first. Recognizing them is important because they retain their systematic names in compound naming.
Common examples include:

• Hydroxide \( \text{OH}^- \)
• Nitrate \( \text{NO}_3^- \)
• Sulfate \( \text{SO}_4^{2-} \)

When naming compounds that contain these ions, like Ba(OH)₂, the polyatomic ion's name remains unchanged, so it is named Barium Hydroxide. Understanding and memorizing common polyatomic ions significantly eases the naming process.

Ionic Compound Naming Rules

Naming ionic compounds follows a clear set of rules that streamline the process. They might seem a bit elaborate, but they ensure uniformity and clarity in chemical communication.Here’s a rundown:

• Begin with the cation: Firstly, name the cation exactly as its element name, such as 'Calcium' for \( \text{Ca} \).
• Identify the anion: If it's a simple anion, the suffix “-ide” is added to the root of the element name. For \( \text{O}^{2-} \), use "oxide".
• For polyatomic ions: Use the standard name these ions are known by, such as "sulfate" for \( \text{SO}_4^{2-} \).
• Complete the name: Combine the names of the cation and anion, ensuring to state them in the order of \( \text{cation} \, ext{anion} \).

Using these rules, a compound like AlPO₄ is named as Aluminum Phosphate. Becoming comfortable with these steps makes chemical naming intuitive and accurate.