Question

Predict the empirical formulas of the ionic compounds formed from the following pairs of elements. Name each compound. a. \(\mathrm{Li}\) and \(\mathrm{N} \quad\) c. \(\mathrm{Rb}\) and \(\mathrm{Cl}\) b. \(\mathrm{Ga}\) and \(\mathrm{O} \quad\) d. \(\mathrm{Ba}\) and \(\mathrm{S}\)

Short answer

The empirical formulas and names of the ionic compounds are: a. \(\mathrm{Li_3N}\): Lithium Nitride b. \(\mathrm{Ga_2O_3}\): Gallium (III) Oxide or Gallium Oxide c. \(\mathrm{RbCl}\): Rubidium Chloride d. \(\mathrm{BaS}\): Barium Sulfide

Step-by-step solution

Identify the charges of the ions involved

Look at the periodic table and determine the ion's charges based on their group number. a. Li and N: Li - Group 1 - Charge: +1 N - Group 15 - Charge: -3 b. Ga and O: Ga - Group 13 - Charge: +3 O - Group 16 - Charge: -2 c. Rb and Cl: Rb - Group 1 - Charge: +1 Cl - Group 17 - Charge: -1 d. Ba and S: Ba - Group 2 - Charge: +2 S - Group 16 - Charge: -2

Determine the smallest whole number ratio

Find the smallest whole number ratio that allows the charges to balance for each pair. a. Li and N: Since N has a charge of -3, we need 3 Li ions to balance the charge. Empirical formula: \(\mathrm{Li_3N}\) b. Ga and O: Since Ga has a charge of +3 and O has a charge of -2, we need 2 Ga ions and 3 O ions to balance the charge. Empirical formula: \(\mathrm{Ga_2O_3}\) c. Rb and Cl: Since the charges of Rb and Cl are +1 and -1, one ion of each can balance the charges. Empirical formula: \(\mathrm{RbCl}\) d. Ba and S: Since both Ba and S have charges of +2 and -2 respectively, one ion of each can balance the charges. Empirical formula: \(\mathrm{BaS}\)

Name each compound

Assign the conventional naming system for each compound. a. \(\mathrm{Li_3N}\): Lithium Nitride b. \(\mathrm{Ga_2O_3}\): Gallium (III) Oxide or Gallium Oxide c. \(\mathrm{RbCl}\): Rubidium Chloride d. \(\mathrm{BaS}\): Barium Sulfide

Key concepts

Empirical Formulas

Empirical formulas are the simplest positive integer ratio of atoms present in a compound. They provide the proportions of elements, rather than the actual number of atoms in molecules. Here's how to find the empirical formula for ionic compounds:

• **Identify the Ion Charges:** Each element in the compound has a specific charge based on its position in the periodic table. For example, lithium has a +1 charge, while nitrogen has a -3 charge.
• **Balance the Charges:** To find the formula, adjust the number of each ion so that the total positive charge equals the total negative charge. In the case of lithium nitride (Li and N), three lithium ions are needed to balance the charge of one nitrogen ion, resulting in the formula \(\mathrm{Li_3N}\).
• **Simplify the Ratio:** Use the smallest whole number that balances the charges. If you find yourself with a ratio like 2:3 as seen with gallium and oxygen to form gallium(III) oxide, use that exact ratio to write \(\mathrm{Ga_2O_3}\).

Empirical formulas are foundational in understanding the composition of compounds, especially for ionic compounds, where atoms transfer electrons to achieve balanced charges.

Periodic Table

The periodic table is a tabular arrangement of elements organized by increasing atomic number and recurring chemical properties. It is a powerful tool for predicting the types of ions they will form, based on their group numbers.
**Understanding Group Numbers:**

• **Group 1 Elements:** Such as lithium (Li) and rubidium (Rb), typically form +1 ions because they have one electron in their outer shell that they "lose" easily.
• **Group 2 Elements:** Include barium (Ba) which forms +2 ions. They have two outer electrons and tend to form ions by losing these electrons.
• **Groups 15, 16, and 17 Elements:** Like nitrogen (N), sulfur (S), chlorine (Cl), and oxygen (O), tend to gain electrons, forming negative ions of -3, -2, and -1 respectively.

Using the periodic table, you can predict empirical formulas after identifying these charges. It not only helps with ionic compounds but also gives insights into chemical behavior.

Chemical Naming Conventions

Chemical naming conventions are rules used to assign names to chemical compounds. For ionic compounds, the naming is straightforward by using the names of the cations (positively charged) and anions (negatively charged).
**Steps in Naming Ionic Compounds:**

• **Cation Comes First:** Always name the positive ion first. For instance, in \(\mathrm{Li_3N}\), lithium comes before nitride.
• **Anion with Altered Ending:** The anion's name ends with "-ide." In lithium nitride, nitrogen becomes nitride.
• **Transitional Metals:** If the compound includes a metal with variable charges, like gallium in \(\mathrm{Ga_2O_3}\), specify its charge with roman numerals - hence, Gallium (III) Oxide.

These conventions ensure consistent naming of compounds, making it easier to understand and communicate the composition of substances in scientific contexts.