A metal M forms an oxide having the formula M2O3. It belongs to the third period. Write the atomic number and valency of the metal.
The correct answer and explanation is:
Correct Answer:
- Atomic number of metal M: 13
- Valency of metal M: 3
Explanation (Approx. 300 Words)
The oxide of the metal is given as M₂O₃. To deduce the atomic number and valency of the metal, let’s analyze the chemical formula:
- Determine the valency:
- Oxygen typically has a valency of –2.
- In M₂O₃, there are 3 oxygen atoms, each contributing –2, giving a total charge of –6.
- To balance this, the two metal atoms must together contribute a total of +6 charge.
- Therefore, each metal atom contributes +3.
- Valency of metal M is +3.
- Identify the metal from Period 3 with +3 valency:
- The third period of the periodic table includes the following elements (atomic numbers in parentheses):
- Na (11), Mg (12), Al (13), Si (14), P (15), S (16), Cl (17), Ar (18)
- Among these, aluminum (Al) is the only metal that:
- Forms an oxide with the formula Al₂O₃
- Has a +3 valency
- Is located in the third period
- The third period of the periodic table includes the following elements (atomic numbers in parentheses):
- Confirm atomic number:
- Aluminum (Al) has the atomic number 13
- So, metal M is aluminum, with atomic number 13 and valency 3
- Conclusion:
The oxide M₂O₃ is aluminum oxide (Al₂O₃), where each Al atom has a valency of +3. Since aluminum is in Period 3 and has atomic number 13, the correct answers are:- Atomic number: 13
- Valency: 3
This demonstrates how the chemical formula of a compound, combined with periodic table knowledge, allows us to deduce fundamental properties of an element.