Question

Write the formulas of the following ionic compounds. (a) iron(III) carbonate (b) sodium azide \(\left(\mathrm{N}_{3}-\right)\) (c) calcium sulfate (d) copper(I) sulfide (e) lead(IV) oxide

Short answer

Question: Write the formulas for the following ionic compounds: a) iron(III) carbonate b) sodium azide c) calcium sulfate d) copper(I) sulfide e) lead(IV) oxide Answer: a) Fe2(CO3)3 b) NaN3 c) CaSO4 d) Cu2S e) PbO2

Step-by-step solution

(a) iron(III) carbonate

The iron(III) cation has a charge of +3, written as Fe3+. The carbonate anion has a charge of -2, which is written as CO3^2-. To balance the charges, we need two iron cations (2 x 3+) and three carbonate anions (3 x 2-). The formula for iron(III) carbonate is \(\mathrm{Fe}_{2}(\mathrm{CO}_{3})_{3}\).

(b) sodium azide

Sodium cation (Na+) has a charge of +1 and azide anion (N3-) has a charge of -1. These charges are already balanced, so the formula for sodium azide is \(\mathrm{Na}(\mathrm{N}_{3})\).

(c) calcium sulfate

Calcium cation (Ca2+) has a charge of +2 and the sulfate anion (SO4^2-) has a charge of -2. These charges are already balanced, so the formula for calcium sulfate is \(\mathrm{Ca}(\mathrm{SO}_{4})\).

(d) copper(I) sulfide

The copper(I) cation has a charge of +1, written as Cu+. The sulfide anion has a charge of -2, which is written as S2-. To balance the charges, we need two copper cations (2 x 1+) and one sulfide anion (1 x 2-). The formula for copper(I) sulfide is \(\mathrm{Cu}_{2}\mathrm{S}\).

(e) lead(IV) oxide

The lead(IV) cation has a charge of +4, written as Pb4+. The oxide anion has a charge of -2, which is written as O2-. To balance the charges, we need one lead cation (1 x 4+) and two oxide anions (2 x 2-). The formula for lead(IV) oxide is \(\mathrm{Pb}(\mathrm{O}_{2})\).

Key concepts

Chemical Formulas

Chemical formulas represent the types and numbers of atoms in a compound. They are essential for understanding the composition of ionic compounds. In ionic compounds, positive ions called cations and negative ions called anions come together to form neutral compounds. These chemical formulas show the ratios in which the cations and anions combine. Each element in the formula is represented by its chemical symbol, such as "Fe" for iron or "Na" for sodium.

When writing chemical formulas for ionic compounds, it is important to ensure that the total positive charge from the cations equals the total negative charge from the anions. This neutrality is achieved by adjusting the number of each ion in the compound. For example, in iron(III) carbonate, the formula is written as \( \mathrm{Fe}_{2}(\mathrm{CO}_{3})_{3} \) to balance the charges between iron cations and carbonate anions.

Cation and Anion Charges

Cations and anions form the backbone of ionic compounds, each carrying a distinct charge. Cations are positively charged ions, while anions are negatively charged. For example, the sodium ion \( \text{Na}^+ \) carries a single positive charge, being a cation. On the other hand, the azide ion \( \text{N}_3^- \) carries a single negative charge, being an anion. Understanding these charges is crucial to creating balanced chemical formulas.

The charge of a cation or anion is often predictable based on the periodic table. Elements in the same group tend to form ions with the same charge. Transition metals, however, can form multiple types of cations with different charges, which leads to a concept called transition metal nomenclature. These charges determine how many of each ion will combine to form a neutral ionic compound, as in the case of calcium sulfate. Calcium being \( \text{Ca}^{2+} \) and sulfate being \( \text{SO}_4^{2-} \) readily combine in a one-to-one ratio to produce \( \text{CaSO}_4 \).

Balancing Chemical Formulas

Balancing chemical formulas is a fundamental skill in chemistry, especially for ionic compounds. The goal is to create a formula where the total positive and negative charges are equal, resulting in a neutral compound. If the charges are not balanced, use subscripts to indicate the number of each type of ion needed to achieve balance.

Let's consider the example of copper(I) sulfide. Copper(I) indicates a \( \text{Cu}^+ \) cation with a +1 charge. The sulfide anion \( \text{S}^{2-} \) has a -2 charge. To neutralize the charges, two copper cations combine with one sulfide anion, giving us the balanced formula \( \text{Cu}_2\text{S} \).

• Ensure the total charge of cations equals the total charge of anions.
• Adjust the subscripts to balance charges, never changing the formulas of the ions.

Remember, the key is maintaining the neutrality of the compound.

Transition Metal Nomenclature

Transition metal nomenclature can add complexity to forming chemical formulas due to the metals' ability to have multiple oxidation states. This means they can form cations with different charges. Roman numerals are used in the name of a compound to indicate the specific charge of the transition metal cation involved.

For instance, in iron(III) carbonate, the iron cation \( \text{Fe}^{3+} \) has a charge of +3. The Roman numeral III tells us that we need to consider this specific charge when balancing the formula with carbonate anions \( \text{CO}_3^{2-} \). Another example is lead(IV) oxide, where lead forms a \( \text{Pb}^{4+} \) cation.

• Use Roman numerals to identify the charge of the transition metal.
• Match this charge with the appropriate number of anions to balance the formula.

By understanding transition metal nomenclature, you are better equipped to solve for and understand the structure of ionic compounds involving transition metals.