Question

Write the correct formula for the following compounds: a. aluminum chlorate b. ammonium oxide c. magnesium bicarbonate d. sodium nitrite e. copper(I) sulfate

Short answer

a. Al(ClO₃)₃, b. (NH₄)₂O, c. Mg(HCO₃)₂, d. NaNO₂, e. Cu₂SO₄

Step-by-step solution

Understand the cations and anions

Identify the cation (positive ion) and anion (negative ion) for each compound. For example, aluminum chlorate: the cation is aluminum (Al³⁺) and the anion is chlorate (ClO₃⁻).

Use the Criss-Cross Method

For each compound, use the criss-cross method to balance the charges. For instance, with aluminum chlorate, cross the charges to get Al(ClO₃)₃.

Compose the formula for each compound

a. Aluminum chlorate: Combine Al³⁺ and ClO₃⁻ using criss-cross, resulting in Al(ClO₃)₃. b. Ammonium oxide: Combine NH₄⁺ and O²⁻ using criss-cross, resulting in (NH₄)₂O. c. Magnesium bicarbonate: Combine Mg²⁺ and HCO₃⁻ using criss-cross, resulting in Mg(HCO₃)₂. d. Sodium nitrite: Combine Na⁺ and NO₂⁻ without the need for criss-cross, resulting in NaNO₂. e. Copper(I) sulfate: Combine Cu⁺ and SO₄²⁻ using criss-cross, resulting in Cu₂SO₄.

Key concepts

cation and anion identification

Understanding the basics of ionic compounds starts with identifying cations and anions.

Cations are positively charged ions, while anions are negatively charged ions.

In a chemical formula, the cation is always listed first, followed by the anion. For example, in the compound aluminum chlorate (Al(ClO₃)₃), aluminum is the cation and chlorate is the anion.

Here are some steps to make this identification easier:

• Identify the metal or ammonium group, which is usually the cation.
• Identify the non-metal or polyatomic ion, which tends to be the anion.

With these identifications, you lay a strong foundation for writing correct formulas.

criss-cross method

The criss-cross method is a handy tool to balance the charges of ions in an ionic compound.

It involves taking the numerical value of the charge on the cation and using it as the subscript for the anion, and vice versa.

Let's take aluminum chlorate as an example. Aluminum (Al³⁺) and chlorate (ClO₃⁻) have charges of +3 and -1, respectively. Using the criss-cross method:

• Cross the charges to form subscripts: Al becomes Al(ClO₃)₃.
• Simplify if needed, but in this case, the formula is already simplified: Al(ClO₃)₃.

This method ensures the charges balance out to create a neutral compound.

compound balancing

Balancing compounds is crucial to maintaining charge neutrality. This means the total positive charge should equal the total negative charge.

If using the criss-cross method, make sure to check the following:

• The sum of the charges from the cation(s) and anion(s) should be zero.
• If needed, adjust the subscripts to balance the charges properly. For example, ammonium oxide combines NH₄⁺ with O²⁻. Using the criss-cross method and balancing the charges results in (NH₄)₂O.

Always verify the final formula to ensure accuracy by counting the charges of both ions.

ionic compounds

Ionic compounds are formed by the electrostatic attraction between cations and anions.

These compounds are usually formed when a metal reacts with a non-metal.

Here’s what you need to know:

• Ionic compounds are generally solid at room temperature.
• They have high melting and boiling points due to strong ionic bonds.
• They often dissolve in water and conduct electricity in aqueous solution.

Examples from the exercise include:

• Magnesium bicarbonate (Mg(HCO₃)₂) which is formed from Mg²⁺ and HCO₃⁻.
• Sodium nitrite (NaNO₂) which is formed from Na⁺ and NO₂⁻.

Understanding their properties helps in better understanding their behavior in different conditions.