Problem 21 - Chemistry Matter and Change

Question

Write formulas for the ionic compounds formed by the following ions. aluminum and bromide

Step-by-Step Solution

Answer

The formula for the ionic compound formed is \(\text{AlBr}_3\).

Step 1: Identify the charge of each ion

First, identify the charges associated with each ion. Aluminum (Al) typically forms ions with a +3 charge, denoted as \(\text{Al}^{3+}\). Bromide (Br), on the other hand, is a halogen and forms ions with a -1 charge, written as \(\text{Br}^-\).

Step 2: Determine the ratio of ions needed for charge balance

For the compound to be electrically neutral, the positive and negative charges must balance each other. Since aluminum has a +3 charge and bromide has a -1 charge, you need three bromide ions to balance one aluminum ion. This gives us a ratio of \(1:3\) for aluminum to bromide ions.

Step 3: Write the chemical formula

Using the ratio from Step 2, write the chemical formula by placing the charges in subscript form next to each ion. Therefore, the chemical formula for the compound is \(\text{AlBr}_3\), indicating one aluminum ion coupled with three bromide ions.

Key Concepts

Ionic Compounds

Chemical formula writing for ionic compounds involves understanding the interaction between positively and negatively charged ions. Unlike molecular compounds that share electrons, ionic compounds are formed when electrons are transferred from one atom to another, resulting in a balance of charges. This interaction creates what is known as an "ionic bond."
When aluminum and bromide form an ionic compound, they combine in such a way that their charges are neutralized, creating a stable compound. The resultant compound maintains specific characteristics:

• The structure is composed entirely of ions.
• The compound is electrically neutral.
• It often results in high melting and boiling points due to strong ionic bonds.

Understanding these features is critical for predicting the behavior of ionic compounds in different situations.

Charge Balance

Achieving charge balance is crucial when writing formulas for ionic compounds. This means that the total positive charge must equal the total negative charge, ensuring overall neutrality in the compound.
When you identify ions, like aluminum (\( ext{Al}^{3+}\)) and bromide (\( ext{Br}^-\)), consider their charges:

• Identify the charge of each ion has: +3 for aluminum and -1 for bromide.
• Ensure the total positive charge equals the total negative charge. In this case, three bromide ions (\(3 imes (-1) = -3\)) are necessary to balance one aluminum ion (\(+3\)).

By balancing these charges, you achieve charge neutrality, which is essential for the stability of the ionic compound. This principle is foundational in the study of chemistry, specifically when dealing with ionic compounds.

Subscript Notation

Subscript notation in chemical formulas indicates the number of atoms (or ions) of each element in a compound. It plays a vital role in conveying chemical structure and composition. Understanding subscript notation allows you to represent complex chemical interactions succinctly.
For the aluminum bromide compound, the chemical formula is written as \( ext{AlBr}_3\):

• The absence of a subscript next to aluminum (\( ext{Al}\)) means there is just one aluminum ion.
• The subscript "3" next to bromide (\( ext{Br}_3\)) illustrates three bromide ions needed to balance the single aluminum ion's charge.

Correct use of subscripts ensures both the accurate representation of the compound's makeup and the understood need for charge neutrality.

Ion Charges

Each element in the periodic table tends to exist naturally with a particular charge when it forms ions. This charge reflects the element's ability to lose or gain electrons, leading to stability.
Aluminum, typically, forms cations with a +3 charge, as it loses three electrons to achieve a stable electron configuration. This process results in a distinctly positive ion with notation \( ext{Al}^{3+}\).
Bromine, as a halogen, gains an electron to reach stability, earning it a negative charge with its ion form as \( ext{Br}^-\).
Understanding the charge tendencies of these ions is fundamental when predicting the resulting compounds they can form. Recognizing these specifics aids significantly in chemical formula writing, ensuring accurate charge balance and formation predictions for complex ionic compounds.