Problem 122 - Chemistry Matter and Change

Question

Ionic Compounds Chrysoberyl is a transparent or translucent mineral that is sometimes opalescent. It is composed of beryllium aluminum oxide, BeAl. \(\mathrm{O}_{4}\) . Identify the oxidation numbers of each of the ions found in this compound. Explain the formation of this ionic compound.

Step-by-Step Solution

Answer

Beryllium has +2, aluminum has +3, and oxygen has -2 oxidation states, forming a neutral compound.

Step 1: Identify Elements and Ratios

Chrysoberyl is composed of beryllium (Be), aluminum (Al), and oxygen (O). The chemical formula is BeAlO extsubscript{4}, indicating the presence of one beryllium atom, one aluminum atom, and four oxygen atoms.

Step 2: Assign Known Oxidation Numbers

Oxygen is a common element with a known oxidation number. It typically has an oxidation state of -2. Since there are four oxygen atoms, the total oxidation number for oxygen in BeAlO extsubscript{4} is 4 imes (-2) = -8.

Step 3: Determine Oxidation States of Metals

The beryllium and aluminum atoms' oxidation numbers must balance the -8 from the oxygen. Assign the oxidation states of beryllium as +2 and aluminum as +3, as they typically display these oxidation states in compounds.

Step 4: Balance Oxidation Numbers

The sum of the oxidation numbers must equal zero for the compound to be neutral. Thus, +2 (for Be) + +3 (for Al) + -8 (for 4O) = -3. To achieve neutrality in this compound, the oxidation state of Al is typically +3.

Step 5: Confirm Stability of the Compound

Verify if Be with +2, Al with +3, and 4O with -2 each create a neutral compound: \(+2 \times 1 \text{(Be)} + +3 \times 1 \text{(Al)} + -2 \times 4 \text{(O)} = 0.\) This confirms the compound's neutrality.

Key Concepts

Oxidation Numbers

Oxidation numbers are essential in understanding how atoms interact in a compound. They tell us how many electrons an atom either gains or loses when forming a compound. Generally, oxidation numbers can also help us balance chemical equations.
In the context of beryllium aluminum oxide, we first assign oxidation numbers to common elements like oxygen, which usually carries an oxidation state of (-2). Given there are four oxygen atoms in the compound (BeAlO₄), the total oxidation contribution of oxygen is calculated as (-2) × 4 = -8.
For metals like beryllium and aluminum, we assign their usual oxidation states: beryllium ( +2) and aluminum ( +3). Balancing these numbers ensures that the entire compound remains electrically neutral, important for stability.

Beryllium Aluminum Oxide

Beryllium aluminum oxide is a fascinating compound better known as chrysoberyl. This mineral is often found in nature as a transparent gem, sometimes opalescent, which is prized for its beauty. The chemical formula for beryllium aluminum oxide is BeAlO₄.
The compound showcases how three different elements—beryllium, aluminum, and oxygen—combine to form a stable substance. Beryllium is a light element that contributes (+2) to the compound's overall charge. Aluminum follows with (+3), bringing additional stability, while oxygen's (-2) from each atom balances out the metals' positive charges to maintain neutrality. This intricate balance between the oxidation states is what makes the compound stable and naturally occurring.

Chemical Formula

A chemical formula provides crucial information about the composition of a substance. It's expressed in terms of the kinds and proportions of atoms in a compound. For beryllium aluminum oxide, the formula is written as BeAlO₄.
This formula indicates that the compound contains one beryllium atom, one aluminum atom, and four oxygen atoms. By understanding the chemical formula, we can deduce the ratio of atoms in the compound, which further helps in assigning oxidation numbers.

• Beryllium: 1 atom
• Aluminum: 1 atom
• Oxygen: 4 atoms

Knowing the chemical formula allows chemists to understand and predict how a substance will react with others and assess its properties.

Neutral Compound

The term "neutral compound" refers to a compound whose overall net charge is zero. This means the sum of positive charges equates to the sum of negative charges within the compound.
For ionic compounds such as beryllium aluminum oxide, neutrality is achieved through the careful balance of oxidation numbers. Here, the positive charges from beryllium ( +2) and aluminum ( +3) balance out the negative charge from the four oxygen atoms ( -2 each), resulting in a neutral compound:

• Beryllium contributes +2.
• Aluminum contributes +3.
• Oxygen collectively contributes (-8).

Together, (2+3-8=0), satisfying the requirement for neutrality. This balance is crucial, as neutral compounds often possess greater stability compared to charged species.