Question:
The set of molecules in which the central atom is not obeying the octet rule is
The set of molecules in which the central atom is not obeying the octet rule is
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Elements of the third period and beyond can show expanded octet because they can accommodate more than \(8\) electrons in their valence shell.
Updated On: Jun 22, 2026
- \(CO_2,\; SiH_4,\; BeCl_2\)
- \(H_2O,\; Cl_2O,\; CO_2\)
- \(CH_4,\; NH_3,\; OF_2\)
- \(SF_6,\; PCl_5,\; XeF_2\)
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The Correct Option is D
Solution and Explanation
Step 1: Understand the octet rule.
According to the octet rule, atoms generally tend to have \(8\) electrons in their valence shell after bond formation.
However, some atoms can have an expanded octet, especially elements from the third period and beyond.
Step 2: Check the molecules in option (4).
In \(SF_6\), sulphur is the central atom and forms \(6\) bonds with fluorine atoms.
So, sulphur has \(12\) electrons around it, which is more than an octet.
In \(PCl_5\), phosphorus is the central atom and forms \(5\) bonds with chlorine atoms.
So, phosphorus has \(10\) electrons around it, which is more than an octet.
In \(XeF_2\), xenon is the central atom and forms \(2\) bonds with fluorine atoms along with lone pairs.
Xenon also has more than \(8\) electrons around it.
Step 3: Compare with other options.
Molecules like \(H_2O\), \(CO_2\), \(CH_4\), \(NH_3\), and \(OF_2\) generally obey the octet rule.
Therefore, option (4) contains molecules in which the central atom does not obey the octet rule.
Step 4: Final conclusion.
Hence, the required set is:
\[ \boxed{SF_6,\; PCl_5,\; XeF_2} \]
According to the octet rule, atoms generally tend to have \(8\) electrons in their valence shell after bond formation.
However, some atoms can have an expanded octet, especially elements from the third period and beyond.
Step 2: Check the molecules in option (4).
In \(SF_6\), sulphur is the central atom and forms \(6\) bonds with fluorine atoms.
So, sulphur has \(12\) electrons around it, which is more than an octet.
In \(PCl_5\), phosphorus is the central atom and forms \(5\) bonds with chlorine atoms.
So, phosphorus has \(10\) electrons around it, which is more than an octet.
In \(XeF_2\), xenon is the central atom and forms \(2\) bonds with fluorine atoms along with lone pairs.
Xenon also has more than \(8\) electrons around it.
Step 3: Compare with other options.
Molecules like \(H_2O\), \(CO_2\), \(CH_4\), \(NH_3\), and \(OF_2\) generally obey the octet rule.
Therefore, option (4) contains molecules in which the central atom does not obey the octet rule.
Step 4: Final conclusion.
Hence, the required set is:
\[ \boxed{SF_6,\; PCl_5,\; XeF_2} \]
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