Question

Write the formula for each of these ionic substances. a. plumbic oxide b. stannous bromide c. cupric sulfide d. cuprous iodide e. mercurous chloride f. chromic fluoride

Short answer

a. \(PbO_2\) b. \(SnBr_2\) c. \(CuS\) d. \(CuI\) e. \(Hg_2Cl_2\) f. \(CrF_3\)

Step-by-step solution

Identify the ions and their charges

Plumbic ion is Pb(IV), which means it has a charge of +4. Oxide ion is O, which has a charge of -2.

Write the formula

To neutralize the charges, we need 2 oxide ions for each plumbic ion. Therefore, the formula for plumbic oxide is: PbO₂ b. Stannous bromide

Identify the ions and their charges

Stannous ion is Sn(II), which means it has a charge of +2. Bromide ion is Br, which has a charge of -1.

Write the formula

To neutralize the charges, we need 2 bromide ions for each stannous ion. Therefore, the formula for stannous bromide is: SnBr₂ c. Cupric sulfide

Identify the ions and their charges

Cupric ion is Cu(II), which means it has a charge of +2. Sulfide ion is S, which has a charge of -2.

Write the formula

To neutralize the charges, we need 1 sulfide ion for each cupric ion. Therefore, the formula for cupric sulfide is: CuS d. Cuprous iodide

Identify the ions and their charges

Cuprous ion is Cu(I), which means it has a charge of +1. Iodide ion is I, which has a charge of -1.

Write the formula

To neutralize the charges, we need 1 iodide ion for each cuprous ion. Therefore, the formula for cuprous iodide is: CuI e. Mercurous chloride

Identify the ions and their charges

Mercurous ion is Hg₂²⁺, which means it has a charge of +2. Chloride ion is Cl, which has a charge of -1.

Write the formula

To neutralize the charges, we need 2 chloride ions for each mercurous ion. Therefore, the formula for mercurous chloride is: Hg₂Cl₂ f. Chromic fluoride

Identify the ions and their charges

Chromic ion is Cr(III), which means it has a charge of +3. Fluoride ion is F, which has a charge of -1.

Write the formula

To neutralize the charges, we need 3 fluoride ions for each chromic ion. Therefore, the formula for chromic fluoride is: CrF₃

Key concepts

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons from one to another, resulting in the formation of ions. These ions are atoms or molecules that carry a net electric charge, due to the loss or gain of electrons. For ionic compounds, we find two main types of ions: cations and anions. Cations are positively charged ions formed when an atom loses electrons. Anions are negatively charged ions formed when an atom gains electrons.

• Cations are typically metal ions like Na⁺, Ca²⁺, and Al³⁺.
• Anions are typically non-metal ions like Cl⁻, O²⁻, and S²⁻.

Ionic compounds generally exist in solid form at room temperature. They have high melting and boiling points due to the strong electrostatic force between the oppositely charged ions. On dissolving in water, they often dissociate into their respective ions, which makes them good conductors of electricity in solution.

Ion Charges

Understanding ion charges is key to predicting how ions will combine to form ionic compounds. The charge on an ion is determined by the number of electrons lost or gained by an atom in order to achieve a full outer electron shell, which is usually the most stable configuration for an atom.
Different elements gain or lose different numbers of electrons depending on their position in the periodic table:

• Group 1 elements (alkali metals) form +1 cations, like Li⁺.
• Group 2 elements (alkaline earth metals) form +2 cations, like Mg²⁺.
• Group 17 elements (halogens) form -1 anions, like Cl⁻.

Some transition metals can form more than one type of ion. For instance, copper can form Cu⁺ or Cu²⁺, and iron can form Fe²⁺ or Fe³⁺. In such cases, the ion charges are indicated in the name of the compound using roman numerals. Understanding these charge states is crucial when writing the chemical formulas of ionic compounds.

Neutralization of Charges

Neutralization of charges is essential for writing the correct chemical formula for ionic compounds. This process involves balancing the total positive charge with the total negative charge, ensuring that the resulting compound is electrically neutral.

When forming ionic compounds, the charges of the cations and anions must cancel each other out. This is done by combining the ions in specific ratios:

• For example, to neutralize the +2 charge of a calcium ion (Ca²⁺) with the -1 charge of a chloride ion (Cl⁻), two chloride ions are needed: CaCl₂.
• Similarly, aluminum ions (Al³⁺) can be neutralized with oxide ions (O²⁻) by using two aluminum ions for every three oxide ions: Al₂O₃.

Forming ionic compounds requires a deep understanding of how to balance these charges to ensure the compound is stable and neutral. This understanding allows us to predict and write the formulas of various ionic substances correctly, as demonstrated in chemical problems and exercises.