What is the valency of aluminum in \(\mathrm{Al}_{2} \mathrm{O}_{3} ?\)
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Understanding Valency in \(\mathrm{Al}_{2} \mathrm{O}_{3}\)
The question asks about the valency of aluminum in the compound aluminum oxide, which has the chemical formula \(\mathrm{Al}_{2} \mathrm{O}_{3}\). Valency is the combining capacity of an element, or the number of electrons an atom gains, loses, or shares to form chemical bonds.
In ionic compounds like aluminum oxide, valency corresponds to the magnitude of the charge on the ion. Aluminum oxide is formed from aluminum (Al) and oxygen (O) elements.
Analyzing the Chemical Formula \(\mathrm{Al}_{2} \mathrm{O}_{3}\)
The formula \(\mathrm{Al}_{2} \mathrm{O}_{3}\) tells us that:
- There are 2 atoms of aluminum.
- There are 3 atoms of oxygen.
Compounds are electrically neutral overall. This means the total positive charge from the metal ions must balance the total negative charge from the non-metal ions.
Determining Valency Using Known Elements
We typically know the valency of common elements, or their usual oxidation states in compounds. Oxygen is a very common element, and in most oxides, its valency is 2 (or oxidation state is -2).
Let's assume the valency of oxygen is 2. The total negative valency contributed by 3 oxygen atoms is \(3 \times 2 = 6\).
Since the compound is neutral, the total positive valency contributed by 2 aluminum atoms must balance this, meaning the total positive valency is also 6.
If the valency of one aluminum atom is \(x\), then the total valency from 2 aluminum atoms is \(2 \times x\).
Setting the total positive and negative valencies equal:
\(2 \times x = 6\)
Now, we solve for \(x\):
\(x = \frac{6}{2}\)
\(x = 3\)
Therefore, the valency of aluminum in \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is 3.
Summary of Valency Calculation
| Element | Number of Atoms in \(\mathrm{Al}_{2} \mathrm{O}_{3}\) | Valency (assumed/unknown) | Total Valency Contribution |
|---|---|---|---|
| Aluminum (Al) | 2 | \(x\) | \(2 \times x\) |
| Oxygen (O) | 3 | 2 | \(3 \times 2 = 6\) |
Equating total positive and negative valency for a neutral compound:
\(2x = 6\)
\(x = 3\)
The valency of aluminum in \(\mathrm{Al}_{2} \mathrm{O}_{3}\) is 3.
Revision Table: Valency Concepts
| Term | Definition | Example |
|---|---|---|
| Valency | The combining capacity of an element, often equal to the number of electrons gained, lost, or shared. | Valency of H is 1, O is 2 (usually), Cl is 1. |
| Chemical Formula | A symbolic representation showing the types and numbers of atoms in a compound. | \(\mathrm{H}_{2}\mathrm{O}\) (Water), \(\mathrm{NaCl}\) (Sodium Chloride), \(\mathrm{Al}_{2}\mathrm{O}_{3}\) (Aluminum Oxide). |
| Ionic Compound | A compound formed by electrostatic attraction between oppositely charged ions, resulting from the transfer of electrons. | \(\mathrm{NaCl}\), \(\mathrm{MgCl}_{2}\), \(\mathrm{Al}_{2}\mathrm{O}_{3}\). |
Additional Information on Aluminum Valency
Aluminum (Al) is a Group 13 element. Elements in Group 13 typically lose 3 valence electrons to achieve a stable electron configuration, forming ions with a +3 charge. This corresponds to a valency of 3. This is why aluminum commonly exhibits a valency of 3 in most of its compounds, including aluminum oxide (\(\mathrm{Al}_{2} \mathrm{O}_{3}\)).
The concept of valency is closely related to oxidation state, especially for elements in ionic compounds. In \(\mathrm{Al}_{2} \mathrm{O}_{3}\), the oxidation state of oxygen is -2, and the oxidation state of aluminum is +3. The magnitude of the oxidation state (3 for Al, 2 for O) corresponds to their valencies in this compound.
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