Problem 11 - Chemistry and Chemical Reactivity

Question

Predict the charges of the ions in an ionic compound containing the elements barium and bromine. Write the formula for the compound.

Step-by-Step Solution

Answer

The compound is BaBr₂, with a 1:2 ratio of Ba²⁺ to Br⁻ ions.

Step 1: Identify the Elements and Their Groups

We start by identifying the elements involved: barium (Ba) and bromine (Br). Barium is an alkaline earth metal located in Group 2 of the periodic table, while bromine is a halogen located in Group 17.

Step 2: Determine the Charges on the Ions

Elements form ions based on their group numbers. Barium, being in Group 2, typically loses 2 electrons to form a cation with a charge of +2: \( \text{Ba}^{2+} \). Bromine, being in Group 17, typically gains 1 electron to form an anion with a charge of -1: \( \text{Br}^- \).

Step 3: Balance the Charges

For ionic compounds, the total charge must be zero. Barium has a charge of +2, and each bromine has a charge of -1. To balance the charges, two bromine ions are needed for each barium ion: \( 1 \times (+2) + 2 \times (-1) = 0 \).

Step 4: Write the Chemical Formula

Based on the balanced charges, the chemical formula for the compound is written by placing the cation first followed by the anion, indicating the number of each ion in the subscript if there is more than one. The formula is \( \text{BaBr}_2 \).

Key Concepts

Barium Ion

Barium is a chemical element positioned in Group 2 of the periodic table, known as the alkaline earth metals. These metals have a common characteristic where they typically lose two electrons to achieve a stable electron configuration, similar to the nearest noble gas. Hence, the barium atom () loses two electrons to form the barium ion () with a charge of +2. This process of losing electrons gives barium its characteristic cationic form, represented as \( \text{Ba}^{2+} \).

• Group 2 elements like barium are typically reactive.
• They tend to lose two electrons to form positive ions.

Understanding how barium becomes a positively charged ion helps in predicting its behavior in forming ionic compounds, especially with nonmetals like bromine.

Bromine Ion

Bromine is a member of the halogen group found in Group 17 of the periodic table. Halogens are known for their strong tendency to acquire one additional electron to complete their outer shell and achieve noble gas electron configuration. This results in the formation of a negatively charged ion. Specifically, a bromine atom () gains one electron to become a bromide ion () with a charge of -1, denoted as \( \text{Br}^- \). This transformation is crucial for forming ionic bonds.

• Acquiring one more electron allows bromine to become negatively charged.
• This desire to gain electrons makes halogens highly reactive.

The negative charge on the bromine ion plays a vital role in neutralizing charges in ionic compounds.

Chemical Formula

Chemical formulas are essential for conveying the composition of compounds. The formula of an ionic compound shows the ratio of the ions involved, reflecting how these ions balance each other's charge to achieve electrical neutrality. For barium and bromine, the respective ions are \( \text{Ba}^{2+} \) and \( \text{Br}^- \).Given that the charge on barium is +2 and on bromine is -1, two bromide ions are needed to balance the +2 charge of one barium ion. This one-to-two ratio ensures that the overall charge of the compound is zero, which is necessary for stability. Hence, the chemical formula for the compound is \( \text{BaBr}_2 \).

• The cation (positive ion) is written first in the formula.
• Subscripts indicate the number of ions needed.

Understanding chemical formulas is essential for writing formulas correctly and predicting how elements will interact.

Charge Balance

Charge balance is a fundamental rule in ionic compound formation. The overall charge of any ionic compound must equal zero to be stable. This is achieved by balancing the total positive charge of the cations with the total negative charge of the anions. In the case of barium and bromine, understanding their respective charges (\( \text{Ba}^{2+} \) and \( \text{Br}^- \)) allows us to determine the ratio needed to achieve charge neutrality.For \( \text{BaBr}_2 \), the charges are balanced:\[1 \times (+2) + 2 \times (-1) = 0.\]This indicates that one barium ion with a +2 charge pairs with two bromine ions each having a -1 charge. This pairing ensures no excess charge remains, which is crucial for the formation of a stable compound.

• Ionic compounds must be electrically neutral.
• Charge balancing dictates the formula of the compound.

Mastering charge balance is critical in determining the correct formula for an ionic compound.