Question

Write the chemical formulas for the following compounds: (a) aluminum hydroxide, \((\mathbf{b})\) potassium sulfate, \((\mathbf{c})\) copper(I) oxide, \((\mathbf{d})\) zinc nitrate, \((\mathbf{e})\) mercury(II) bromide, (f) iron(III) carbonate, \((\mathbf{g})\) sodium hypobromite.

Short answer

The chemical formulas for the given compounds are: (a) Aluminum Hydroxide: Al(OH)₃ (b) Potassium Sulfate: K₂SO₄ (c) Copper(I) Oxide: Cu₂O (d) Zinc Nitrate: Zn(NO3)₂ (e) Mercury(II) Bromide: HgBr₂ (f) Iron(III) Carbonate: Fe₂(CO₃)₃ (g) Sodium Hypobromite: NaBrO

Step-by-step solution

(a) Aluminum Hydroxide

First, find the charges of aluminum (Al) and hydroxide (OH). Aluminum has a charge of +3, and hydroxide has a charge of -1. Combine them in the ratio that ensures a neutral compound: one aluminum for every three hydroxides. The chemical formula for aluminum hydroxide is: Al(OH)₃.

(b) Potassium Sulfate

First, find the charges of potassium (K) and sulfate (SO4). Potassium has a charge of +1, and sulfate has a charge of -2. Combine them in the ratio that ensures a neutral compound: two potassium ions for every sulfate ion. The chemical formula for potassium sulfate is: K₂SO₄.

(c) Copper(I) Oxide

First, find the charges of copper (Cu) and oxide (O). Since this is copper(I), its charge is +1, and oxide has a charge of -2. Combine them in the ratio that ensures a neutral compound: two copper ions for every oxide ion. The chemical formula for copper(I) oxide is: Cu₂O.

(d) Zinc Nitrate

First, find the charges of zinc (Zn) and nitrate (NO3). Zinc has a charge of +2, and nitrate has a charge of -1. Combine them in the ratio that ensures a neutral compound: one zinc ion for every two nitrate ions. The chemical formula for zinc nitrate is: Zn(NO3)₂.

(e) Mercury(II) Bromide

First, find the charges of mercury (Hg) and bromide (Br). Since this is mercury(II), its charge is +2, and bromide has a charge of -1. Combine them in the ratio that ensures a neutral compound: one mercury ion for every two bromide ions. The chemical formula for mercury(II) bromide is: HgBr₂.

(f) Iron(III) Carbonate

First, find the charges of iron (Fe) and carbonate (CO3). Since this is iron(III), its charge is +3, and carbonate has a charge of -2. Combine them in the ratio that ensures a neutral compound: two iron ions for every three carbonate ions. The chemical formula for iron(III) carbonate is: Fe₂(CO₃)₃.

(g) Sodium Hypobromite

First, find the charges of sodium (Na) and hypobromite (BrO). Sodium has a charge of +1, and hypobromite has a charge of -1. Combine them in the ratio that ensures a neutral compound: one sodium ion for every hypobromite ion. The chemical formula for sodium hypobromite is: NaBrO.

Key concepts

Ionic Compounds

Ionic compounds are chemical compounds composed of ions that are held together by electrostatic forces termed ionic bonds. These compounds usually form between metals and non-metals. When a metal bonds with a non-metal, electrons are transferred from the metal to the non-metal, resulting in the formation of positive and negative ions.
These oppositely charged ions attract each other, forming a stable ionic compound. For example, in aluminum hydroxide, aluminum and hydroxide ions pair to create the compound with the formula \( \text{Al(OH)}_3 \), where three hydroxide ions balance the charge of one aluminum ion.

• Ionic compounds generally have high melting and boiling points due to strong ionic bonds.
• They tend to dissolve in water and conduct electricity when dissolved.
• The formula of an ionic compound represents the specific ratio of ions for charge balance, not the number of ions in the compound itself.

Charge Balancing

To write the chemical formula of an ionic compound, charge balancing is crucial. The charges of the cations (positive ions) and anions (negative ions) must be neutralized to form a stable compound.
This requires that the total positive charge equals the total negative charge. For instance, in the compound zinc nitrate \( \text{Zn(NO}_3\text{)}_2 \), zinc carries a charge of \(+2\) while each nitrate carries \(-1\). Two nitrate ions balance the charge of one zinc ion.

• Positive and negative charges must always cancel each other out.
• If the charges do not exactly balance as whole numbers, multiply the number of ions until they do.
• Write the compound formula based on the minimal ratio of ions needed for charge balance.

Compound Naming Conventions

Naming ionic compounds follows specific conventions. The metal, or cation, is named first, followed by the non-metal or polyatomic ion anion. For example, with iron(III) carbonate, 'iron' refers to the metal ion \( \text{Fe}^{3+} \), and 'carbonate' refers to the anion \( \text{CO}_3^{2-} \).
For metals that can have more than one ionic charge, a Roman numeral in parentheses indicates the ion's charge, as in copper(I) oxide. Here 'I' indicates a charge of \(+1\) for copper.

• The name often reflects the composition and type of ions in the compound.
• Polyatomic ions (like sulfate \( \text{SO}_4^{2-} \) or nitrate \( \text{NO}_3^-\)) retain their standard names within compounds.
• Greek prefixes are rarely used, except in molecular compounds, not in ionic ones.

Ionic Charges

Ions form when atoms lose or gain electrons, resulting in a charge. Metals on the periodic table tend to lose electrons forming positive cations, whereas non-metals gain electrons forming negative anions.
The magnitude of charge is often predictable based on the group number for main block elements. For example:

• Group 1 metals form \(+1\) cations, like sodium \( \text{Na}^+ \).
• Group 2 metals form \(+2\) cations, like zinc \( \text{Zn}^{2+} \).
• Transition metals can have varying charges; Roman numerals indicate their actual charge in compounds, like mercury(II) in HgBr₀ which is \(+2\).
• Common non-metal charges involve gaining enough electrons to fill a valence shell, like hydroxide \( \text{OH}^- \) which has a charge of \(-1\).

Neutral Compounds

Neutral compounds are the goal in forming ionic compounds. A neutral compound is one where the sum of all positive and negative charges equals zero.
This charge neutrality provides stability to the compound. Writing formulas correctly ensures neutrality, which can be seen in compounds like potassium sulfate, \( \text{K}_2\text{SO}_4 \), where two potassium ions \( \text{K}^+ \) balance one sulfate ion \( \text{SO}_4^{2-} \).

• No net charge should exist in the formula unit of an ionic compound.
• Balancing charges often involves adjusting the ratio of ions.
• The smallest whole number ratio achieving neutrality should be used in writing any ionic formula.