Problem 140 - Chemistry Matter and Change

Question

Write the correct chemical name for each compound. (Chapter 7\()\) $$ \begin{array}{l}{\text { a. } \mathrm{NaI}} \\ {\text { b. } \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{3}} \\ {\text { c. } \mathrm{Sr}(\mathrm{OH})_{2}} \\ {\text { d. } \mathrm{CoCl}_{2}} \\ {\text { e. } \mathrm{Mg}\left(\mathrm{BrO}_{3}\right)_{2}}\end{array} $$

Step-by-Step Solution

Answer

a. Sodium Iodide, b. Iron(III) Nitrate, c. Strontium Hydroxide, d. Cobalt(II) Chloride, e. Magnesium Bromate.

Step 1: Identify the Ionic Components (a)

The compound \( \text{NaI} \) consists of sodium (Na) and iodide (I). Sodium is a Group 1 element with a +1 charge, and iodide is a halogen with a -1 charge.

Step 2: Name the Compound (a)

Since Na is sodium and I is iodide, the compound \( \text{NaI} \) is named Sodium Iodide.

Step 3: Identify the Ionic Components (b)

The compound \( \text{Fe(NO}_3)_3 \) is composed of iron (Fe) and the nitrate ion \((\text{NO}_3^-)\). Iron can have multiple oxidation states; however, since there are three nitrates each with a charge of -1, the charge on iron must be +3.

Step 4: Name the Compound (b)

Given the +3 oxidation state of iron, the compound is named Iron(III) Nitrate.

Step 5: Identify the Ionic Components (c)

The compound \( \text{Sr(OH)}_2 \) consists of strontium (Sr) and the hydroxide ion \((\text{OH}^-)\). Strontium is an alkaline earth metal with a +2 charge.

Step 6: Name the Compound (c)

The compound is named Strontium Hydroxide.

Step 7: Identify the Ionic Components (d)

The compound \( \text{CoCl}_2 \) includes cobalt (Co) and chloride (Cl) ions. Cobalt can have different oxidation states, but this compound uses cobalt in the +2 oxidation state.

Step 8: Name the Compound (d)

The correct name for the compound \( \text{CoCl}_2 \) is Cobalt(II) Chloride.

Step 9: Identify the Ionic Components (e)

The compound \( \text{Mg(BrO}_3)_2 \) is made of magnesium (Mg) and the bromate ion \((\text{BrO}_3^-)\). Magnesium is in Group 2 and has a +2 charge.

Step 10: Name the Compound (e)

The compound \( \text{Mg(BrO}_3)_2 \) is therefore named Magnesium Bromate.

Key Concepts

Ionic Compounds

Ionic compounds are formed when atoms bond together through the transfer of electrons. They are composed of positive ions, known as cations, and negative ions, called anions. The resulting chemical formula represents the balance of total positive and negative charges. Each compound must be electrically neutral overall.

To name ionic compounds, follow these simple steps:

• Begin with the name of the cation (positive ion).
• Follow with the name of the anion (negative ion), often ending in '-ide' if it is a monoatomic ion.

For example, in the compound \( \text{NaI} \), sodium (Na) is the cation, and iodide (I) is the anion. The compound is named "Sodium Iodide.”

However, if the anion is a polyatomic ion such as nitrate \( \text{(NO}_3^-) \), then the compound takes the name of the polyatomic ion, like "Iron(III) Nitrate" in \( \text{Fe(NO}_3)_3 \). Remember, ionic compounds often demonstrate the charge balance principle, where the total positive and negative charges must neutralize each other.

Oxidation States

An atom's oxidation state is a conceptual tool that helps us understand the electron distribution in a compound. It represents the hypothetical charge that an atom would have if all the bonds were ionic. The concept of oxidation state is crucial for naming transition metal ions, which can exhibit multiple oxidation states.

For instance, in \( \text{Fe(NO}_3)_3 \), iron can exist in multiple oxidation states. Here, the oxidation state is determined by balancing the overall charge of the compound. Since each nitrate ion \( \text{(NO}_3^-) \) has a charge of -1 and there are three such ions, iron must have an oxidation state of +3 to balance these charges, resulting in "Iron(III) Nitrate."

The digits in parentheses, like (III) in Iron(III) Nitrate, denote the oxidation state of the metal ion in the compound. Being consistent and precise with oxidation states helps clearly communicate the chemical identity of the compound.

Polyatomic Ions

Polyatomic ions are ions that consist of two or more atoms covalently bonded, or of a metal complex that acts as a single unit with a net charge. They are key in forming ionic compounds beyond simple two-element combinations.

Some common polyatomic ions include nitrate \( \text{NO}_3^- \), hydroxide \( \text{OH}^- \), and bromate \( \text{BrO}_3^- \). These ions carry their own respective charges and are involved in forming compounds like \( \text{Fe(NO}_3)_3 \), \( \text{Sr(OH)}_2 \), and \( \text{Mg(BrO}_3)_2 \).

When naming compounds with polyatomic ions, the name of the ion is retained. For example, \( \text{Mg(BrO}_3)_2 \) is called "Magnesium Bromate," where "Bromate" refers specifically to the \( \text{BrO}_3^- \) ion. Recognizing these ions and knowing their charges is essential for understanding the composition and naming of various ionic compounds.