Question

Give the formulas of compounds in which (a) the cation is \(\mathrm{Ba}^{2+}\), the anion is \(\mathrm{I}^{-}\) or \(\mathrm{N}^{3-}\). (b) the anion is \(\mathrm{O}^{2-}\), the cation is \(\mathrm{Fe}^{2+}\) or \(\mathrm{Fe}^{3+}\)

Short answer

a) Ba2+ with I- and N3- b) O2- with Fe2+ and Fe3+ Answer: The formulas of the compounds are: a) BaI2 and Ba3N2 b) FeO and Fe2O3

Step-by-step solution

Forming compounds with Ba2+

For the first compound, we have \(\mathrm{Ba}^{2+}\) as the cation and \(\mathrm{I}^{-}\) as the anion. In order to balance the charge, we need 2 iodide anions for each barium cation. Therefore, the formula for this compound is \(\mathrm{BaI}_{2}\). For the second compound, we have \(\mathrm{Ba}^{2+}\) as the cation and \(\mathrm{N}^{3-}\) as the anion. In order to balance the charge, we need 3 barium cations for every 2 nitride anions. Therefore, the formula for this compound is \(\mathrm{Ba}_{3}\mathrm{N}_{2}\).

Forming compounds with O2-

For the first compound, we have \(\mathrm{O}^{2-}\) as the anion and \(\mathrm{Fe}^{2+}\) as the cation. In order to balance the charge, we need one of each ion type. Therefore, the formula for this compound is \(\mathrm{FeO}\). For the second compound, we have \(\mathrm{O}^{2-}\) as the anion and \(\mathrm{Fe}^{3+}\) as the cation. In order to balance the charge, we need 2 oxide anions for each iron(III) cation. Therefore, the formula for this compound is \(\mathrm{Fe}_{2}\mathrm{O}_{3}\). In conclusion, the formulas of the compounds are: (a) \(\mathrm{BaI}_{2}\) and \(\mathrm{Ba}_{3}\mathrm{N}_{2}\) (b) \(\mathrm{FeO}\) and \(\mathrm{Fe}_{2}\mathrm{O}_{3}\)

Key concepts

Cation and Anion Interaction

Chemical compounds form when cations and anions interact. Cations are positively charged ions, meaning they have lost electrons, while anions are negatively charged ions, having gained electrons. This difference in charge results in a strong electrostatic force between them. When a cation encounters an anion, the opposite charges attract each other, leading to the formation of stable compounds.

To understand their interaction, let's look at an example from the provided exercise. Consider the cation \( \mathrm{Ba}^{2+} \) and the anion \( \mathrm{I}^{-} \). Since \( \mathrm{Ba}^{2+} \) has two positive charges, it can pair with two \( \mathrm{I}^{-} \) ions, each having one negative charge, forming \( \mathrm{BaI}_{2} \).

This balancing of charges is fundamental in the formation of ionic compounds, ensuring a perfectly neutral compound, regardless of the sizes and charges of the ions. Each interaction between cation and anion contributes to the structural stability of the resulting compound.

Ionic Compounds

Ionic compounds are substances formed by the chemical binding between cations and anions. These ions associate closely due to their opposite charges. In ionic compounds, the electrons are transferred from the cations to the anions, completing the outer shell of the anion, which is often derived from non-metals.

Most ionic compounds are crystalline solids at room temperature. They have high melting and boiling points due to the strong interactions between the oppositely charged ions. For instance, with \( \mathrm{BaI}_{2} \) formed from \( \mathrm{Ba}^{2+} \) and \( \mathrm{I}^{-} \), the structure typically arranges in a lattice pattern, maximizing the attraction between ions and contributing to high stability.

Understanding the behavior of ionic compounds also explains their solubility in water. Water molecules can surround and separate the ions, allowing them to dissolve. This solubility often affects how we use these compounds in various industrial and laboratory settings, providing a broader understanding of their chemical behavior.

Charge Balancing in Compounds

Charge balancing is a pivotal concept in forming stable ionic compounds. It refers to the requirement that the total positive and negative charges within a compound must be equal. This principle ensures compounds are electrically neutral.

For instance, look at \( \mathrm{Fe}_{2}\mathrm{O}_{3} \). Here, the \( \mathrm{Fe}^{3+} \) ions contribute six positive charges total (2 ions x 3 charges each), while the \( \mathrm{O}^{2-} \) ions contribute six negative charges total (3 ions x 2 charges each). The exchange creates a stable, neutral compound. By following charge balancing, chemists can predict and construct correct formulas by determining the correct ratio of ions needed.

Balancing can require strategic combining of multiple ions to adjust the overall charge. For instance, in \( \mathrm{Ba}_{3}\mathrm{N}_{2} \), the balance is achieved with three \( \mathrm{Ba}^{2+} \) ions counterbalancing the negative charges of two \( \mathrm{N}^{3-} \) ions. This skill of balancing charges is crucial in understanding and predicting reactions and properties of ionic compounds.