QQuestionChemistry
QuestionChemistry
"Which of the following are exceptions to the Lewis octet rule?
(I) CO^2
(II) BeF^2
(III) SF^4
(IV) SO^3
(V) PCl^3"
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Answer
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Step 1:
The Lewis octet rule states that atoms generally prefer to have eight electrons in their valence shell. However, there are exceptions where elements have fewer or more than eight electrons in their valence shell. Let's analyze each molecule to determine if they are exceptions to the Lewis octet rule.
Step 2:(I) CO^2: Carbon has four electrons in its outer shell and oxygen has six.
In a CO^2 molecule, carbon forms double bonds with both oxygen atoms, sharing four electrons from carbon and receiving four from the oxygens. Each oxygen atom also shares two electrons with carbon and brings two of its own. This means that carbon has eight electrons around it, and each oxygen atom has eight as well. Therefore, CO^2 is not an exception to the Lewis octet rule.
Step 3:(II) BeF^2: Beryllium has two electrons in its outer shell and fluorine has seven.
Beryllium forms single bonds with both fluorine atoms, sharing two electrons from beryllium and receiving two from each fluorine atom. This means that beryllium has six electrons around it, which is a violation of the Lewis octet rule.
Step 4:(III) SF^4: Sulfur has six electrons in its outer shell and fluorine has seven.
In SF^4, sulfur forms single bonds with four fluorine atoms, sharing six electrons from sulfur and receiving two from each fluorine atom. This means that sulfur has ten electrons around it, which is an exception to the Lewis octet rule.
Step 5:(IV) SO^3: Sulfur has six electrons in its outer shell and oxygen has six.
In SO^3, sulfur forms double bonds with two oxygen atoms and a single bond with the third oxygen atom. This means that sulfur shares eight electrons with the oxygen atoms and has eight electrons around it. Therefore, SO^3 is not an exception to the Lewis octet rule.
Step 6:(V) PCl^3: Phosphorus has five electrons in its outer shell and chlorine has seven.
In PCl^3, phosphorus forms single bonds with three chlorine atoms, sharing five electrons from phosphorus and receiving three from each chlorine atom. This means that phosphorus has eight electrons around it, which satisfies the Lewis octet rule.
Step 7:
Final Answer
BeF^2 and SF^4 are exceptions to the Lewis octet rule, as they have more than eight electrons in their valence shell.
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