TBR Chemistry, Chapter VIII, Passage 2, question 10

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Why does sp2 Carbon- sp3 Carbon bond have a higher bond energy than an sp3 Carbon- sp3 Carbon bond?

A) An sp2 orbital is shorter than an sp3 orbital, hence the sp2C-sp3C bond is shorter and thus stronger
B) An sp2 orbital is shorter than an sp3 orbital, hence the sp2C-sp3C bond is longer and thus weaker
C) An sp2 orbital is less electronegative than an sp3 orbital, hence the sp2C-sp3C bond is more polar and thus stronger
D) An sp2 orbital is more electronegative than an sp3 orbital, hence the sp2C-sp3C bond is more polar and thus stronger.

Answer: A <--- Highlight to see

My question is: As a rule, do we assume that the greater is the s character, the smaller is the orbital?
Is it because s orbitals have smaller radii than p orbitals?
Why do we automatically assume that shorter orbitals have greater electronegativities?

I honestly don't see how electronegativity and hybridization affect each other...

Thanks!

 

[Gauss44]

Why does sp2 Carbon- sp3 Carbon bond have a higher bond energy than an sp3 Carbon- sp3 Carbon bond?

A) An sp2 orbital is shorter than an sp3 orbital, hence the sp2C-sp3C bond is shorter and thus stronger
B) An sp2 orbital is shorter than an sp3 orbital, hence the sp2C-sp3C bond is longer and thus weaker
C) An sp2 orbital is less electronegative than an sp3 orbital, hence the sp2C-sp3C bond is more polar and thus stronger
D) An sp2 orbital is more electronegative than an sp3 orbital, hence the sp2C-sp3C bond is more polar and thus stronger.

Answer: A <--- Highlight to see


My question is: As a rule, do we assume that the greater is the s character, the smaller is the orbital?
Is it because s orbitals have smaller radii than p orbitals?
Why do we automatically assume that shorter orbitals have greater electronegativities?

I honestly don't see how electronegativity and hybridization affect each other...

Thanks!

1. Yes, if you mean the shorter the bond.
2. I don't think so. I think the shorter bond lengths are due to having more bonds. The greater the s character (sp>sp2>sp3), the more bonds.
3. If you mean shorter bonds, it's because they usually involve more electrons. More electrons in a double bond than a single bond, etc.

 

[mehc012]

1. Yes, if you mean the shorter the bond.
2. I don't think so. I think the shorter bond lengths are due to having more bonds. The greater the s character (sp>sp2>sp3), the more bonds.
3. If you mean shorter bonds, it's because they usually involve more electrons. More electrons in a double bond than a single bond, etc.

You can have a sigma bond with an sp2 orbital. The hybridization might be sp2 because there is a double bond elsewhere: H2C=CH-CH3, for example, has an sp2-sp3 bond betweent he second and 3rd carbon, but that is a single bond.

To the OP, yes...your rationale is correct. An sp2 orbital has more s character than an sp3 orbital, and is therefore closer to the nucleus. In order to overlap with the shorter sp2 orbital, the other atom must get closer than it would have to if it were overlapping with an sp3 orbital. Electronegativity isn't as commonly discussed in this context, but again, an atom with a high electronegativity holds its electrons in close to the nucleus (think about how atomic radius decreases as electronegativity increases) and therefore orbital overlap requires a smaller radius.