Which species has a lone pair of electrons on the central atom?
A CO₂
B SO₂
C PCl₄⁻
D SO₄²⁻ - AQA - A-Level Chemistry - Question 13 - 2021 - Paper 3
Question 13
Which species has a lone pair of electrons on the central atom?
A CO₂
B SO₂
C PCl₄⁻
D SO₄²⁻
Worked Solution & Example Answer:Which species has a lone pair of electrons on the central atom?
A CO₂
B SO₂
C PCl₄⁻
D SO₄²⁻ - AQA - A-Level Chemistry - Question 13 - 2021 - Paper 3
Step 1
Identify the central atom in each species
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Answer
In the case of CO₂, the central atom is carbon (C); for SO₂, it is sulfur (S); for PCl₄⁻, the central atom is phosphorus (P); and for SO₄²⁻, the central atom is sulfur (S).
Next, we analyze the valence electrons of the central atoms to determine if they have lone pairs.
Step 2
Analyze CO₂
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Answer
CO₂ has a linear structure with carbon making double bonds with two oxygen atoms. There are no lone pairs on the central atom (carbon).
Step 3
Analyze SO₂
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Answer
In SO₂, sulfur has six valence electrons. It forms two double bonds with oxygen atoms and has one lone pair remaining on it, confirming that SO₂ has a lone pair on the central atom (sulfur).
Step 4
Analyze PCl₄⁻
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Answer
For PCl₄⁻, phosphorus has five valence electrons and forms four single bonds with chlorine atoms using all its electrons, leaving no lone pairs.
Step 5
Analyze SO₄²⁻
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Answer
In SO₄²⁻, sulfur again forms four bonds with oxygen atoms using all its valence electrons (six), and hence it does not have any lone pairs.
Step 6
Conclusion
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Answer
The only compound that has a lone pair of electrons on the central atom is B) SO₂.
