Question

Write the formulas for the following ionic compounds: (a) sodium oxide, (b) iron sulfide (containing the \(\mathrm{Fe}^{2+}\) ion), (c) cobalt sulfate (containing the \(\mathrm{Co}^{3+}\) and \(\mathrm{SO}_{4}^{2-}\) ions), (d) barium fluoride.

Short answer

(a) Na₂O, (b) FeS, (c) Co₂(SO₄)₃, (d) BaF₂.

Step-by-step solution

Identify the Ions Involved

Identify the cation and anion for each compound. (a) Sodium oxide: Na and O (b) Iron sulfide: Fe²⁺ and S²⁻ (c) Cobalt sulfate: Co³⁺ and SO₄²⁻ (d) Barium fluoride: Ba and F These ions determine the formula based on the charges they carry.

Determine the Compound Formulas

Using the charge information, balance the charges to write the compound formulas. (a) Sodium oxide: Na has a 1+ charge and O has a 2- charge; formula Na₂O. (b) Iron sulfide: Fe²⁺ and S²⁻; charges are balanced with one ion of each, formula FeS. (c) Cobalt sulfate: Co³⁺ and SO₄²⁻; need two Co³⁺ for three SO₄²⁻ ions to balance, formula Co₂(SO₄)₃. (d) Barium fluoride: Ba has a 2+ charge and F has a 1- charge; need two F for each Ba, formula BaF₂.

Key concepts

chemical formulas

Chemical formulas are symbolic representations of the elemental composition of compounds. For ionic compounds, these formulas detail the ratio of cations (positively charged ions) and anions (negatively charged ions) that combine to neutralize each other's charges. These formulas are not random; they are derived from fundamental chemical laws. It is essential to understand

• how each type of ion contributes to the total charge of the compound, and
• how those charges are balanced to create stable, neutral entities.

A formula like sodium oxide, Na₂O, indicates that two sodium cations (Na⁺) bond with one oxide anion (O²⁻) to achieve electrical neutrality. Writing correct chemical formulas ensures accurate chemical communication and proper scientific understanding.

cation and anion identification

Identifying cations and anions is a critical step in writing chemical formulas for ionic compounds. Every ionic compound consists of

• a cation, which is the positively charged ion, and
• an anion, which holds a negative charge.

In the step-by-step exercise, for instance,

• sodium (Na) is the cation and oxygen (O) is the anion in sodium oxide,
• iron(II) ion (\(Fe^{2+}\)) pairs with sulfide (\(S^{2-}\)) in iron sulfide, and
• barium (Ba) acts as the cation with fluoride (F) as the anion in barium fluoride.

Usually, metals lose electrons to become cations, while non-metals gain electrons to become anions. Recognizing the typical charges these elements form is crucial for writing accurate chemical formulas.

charge balancing

After identifying the respective cations and anions, the next crucial step is charge balancing. This involves ensuring that the total positive charge from the cations equals the total negative charge from the anions. The goal:

• Achieve a neutral charge for the entire compound.

For example:

• In sodium oxide (\(Na_2O\)), each sodium ion contributes +1, so we need two of them to balance the -2 charge from one oxygen ion.
• In cobalt sulfate (\(Co_2(SO_4)_3\)), two cobalt (\(Co^{3+}\)) ions provide a total +6 charge, which is balanced by three sulfate (\(SO_4^{2-}\)) ions, each with a -2 charge.

Remember that the charges must always balance out for the compound to be stable, forming a neutral ionic compound.

compound formation

Compound formation in ionic chemistry concerns the interaction and bonding of cations and anions to form a new substance. Ionic bonds result from the electrostatic attraction between these oppositely charged ions. This process:

• Results in a simple and stability-oriented arrangement, often in a crystal lattice.

Each compound forms through specific ratios that allow for charge neutrality and energetic stability, as seen in

• sodium oxide (\(Na_2O\)),
• iron sulfide (\(FeS\)), and
• cobalt sulfate (\(Co_2(SO_4)_3\)).

The lattice structure of ionic compounds helps maximize electrostatic interactions, which helps with high melting and boiling points, as well as greater stability across different conditions. Understanding this process provides insight into the nature and behavior of ionic compounds.