Question 2F.15

[Natallie K 3B]

I am confused on the question 2F.15 from the textbook.

Noting that the bond angle of an sp 3 sp 3 hybridized atom is 109.5° and that of an sp 2 sp 2 hybridized atom is 120°, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?

What does it mean to increase or decrease s-character?

[Shanna Yu 1C]

Hi!

s-character is just another way of saying the extent of sigma bond character in a hybridised structure. With that in mind, angles increase when you increase the s-character.

Let me know if you need clarification/elaboration! I can explain further.

[Melody Wu 2L]

S-character refers to the ratio of the s-orbitals in the hybrid orbitals, or the contribution of sigma bonds in the hybridization. For example, in an sp orbital, since there is one s-orbital and one p-orbital, the s-character is 1/2 or 50%. In an sp^2 orbital, the s-character is 1/3 or 33%. In an sp^3 orbital, it is 1/4 or 25%.

Therefore as the s-character increases, the number of orbitals decreases. The orbitals are farther apart so the bond angle is bigger.
(It helps to consider the molecular shapes too. An sp orbital is linear with 180 degree bond angles vs. an sp^3 orbital is tetrahedral with 109.5 degree bond angles).

[Faith Veenker 2K]

I like to think of it like this: If there is higher proportion of s compared to p (sp^2, 1s:2p has a higher proportion of s than sp^3, 1s:3p), then there is more s-character. As the s-character increases, the bond angle increases (120 for sp^2 >109.5 for sp^3).

[Samuel Flores 1E]

Hello! S-character simply refers to the degree/amount that the s orbital contributes to the hybrid orbital. Remember that hybrid orbitals, like sp2 or sp3 mentioned in the problem, are a combination of s and p orbitals. Therefore, when you increase s character, you increase the extent to which the s orbital contributes to the hybrid orbital.

Hope this helps!

[TJ Lai 2H]

Could someone explain under what circumstances the degree of contribution that a certain orbital (s, p, etc. would increase)? In other words, what would determine the degree of s-character?

[Pranav Daggubati 3C]

the hybridization shows what and how many of each orbital is being hybridized. For example, in and sp3 hybridization, there are 4 orbitals and s is one of them. Therefore, the s-character is 1/4 or 25%. Basically, the more non-s orbitals are hybridized, the less s-character there is.