Bonding, Structure, and Resonance – Sigma bonds come in six varieties: Pi bonds come in one

You might remember from general chemistry (and probably from the first week of organic chemistry) that orbitals on carbon come in two varieties: s and p.

S orbitals, also known as spherical orbitals, should be well-known. For instance, the electrons in hydrogen are in a 1s orbital.

P orbitals resemble loops or figure-eights. The electrons in p orbitals have a slightly higher energy than those in s orbitals because they are a little bit further from the nucleus. As a result, electrons don't fill the p orbitals until the s orbitals are full.

Here, we talk about a concept called hybridization.

The shapes of molecules like CH4 can't be explained by the electrons being in s or p orbitals by themselves; rather, they are the result of the electrons in s and p orbitals combining to form hybrid orbitals. These new orbitals aren't fully s or fully p, but rather a combination of both, similar to how we could create a "hybrid" soft drink by blending various proportions of Sprite and Pepsi. Each bond's "flavour" is determined by the proportions of s and p orbitals present:

25% of the characters in sp3 are s and 75% are p.

33% of the characters in sp2 are s and 66% are p.

sp is made up of 50% s and 50% p characters.

These hybrid orbitals are what create sigma bonds, or bonds. The orbitals collide head-on, forming sigma bonds. The orbitals in question will be a mix of s and p orbitals.

What became of the p orbitals that were missing for sp2 and sp hybridised carbon? These p orbitals, on the other hand, maintain 100% p character and are available to form bonds, which are produced by the side-by-side overlap of orbitals. They aren't involved in hybridization or sigma bonding. Bonding exclusively involves p orbitals.]

We can therefore have six different types of carbon-carbon sigma bonds because carbon can exist in one of these three hybridization states:

Now, keep in mind that s orbitals have lower energies than p orbitals for any given quantum number. Compared to electrons in p orbitals, s orbital electrons are held closer to the nucleus. For each of these six scenarios, consider the relative bond lengths and strengths.

A general rule is that the electrons will be more tightly bound to the bond the more s character it has. [Note 1]

The number of unhybridized p orbitals that are available will now determine how many bonds can form: 1 for sp2 hybridised carbons, and 2 for sp hybridised carbons (in the latter case, the two bonds will be at right angles to one another).

Contrary to sigma orbitals, a C-C bond can only be created by the overlap of two p orbitals.

Do you believe p-p bonds ( bonds) would be stronger or weaker compared to sigma bonds?

What is their percent s-character?

2) Power needed to release the C-C bond in ethane:

Energy necessary to sever the C=C bond in ethene:

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