If all the bonds are in place the shape is also trigonal planar. Hybridization and Electron Pair Geometryįor s and sp hybridized central atoms the only possible molecular geometry is linear, correspondingly the only possible shape is also linear:įor sp2 hybridized central atoms the only possible molecular geometry is trigonal planar.
So if you know the hybridization of an atom you automatically know its EPG. What is really cool about the hybridization is that each hybridization corresponds to an electron pair geometry. What are the hybridizations for each of the central atoms in the following molecule?Īs you can see from the example above, assigning the hybridization to each central atom is easy as long as you can count to 6. The following rules give the hybridization of the central atom:ġ bond to another atom or lone pair = s (not really hybridized)Ģ bonds to another atom or lone pairs = spģ bonds to another atom or lone pairs = sp 2Ĥ bonds to another atom or lone pairs = sp 3ĥ bonds to another atom or lone pairs = sp 3dĦ bonds to another atom or lone pairs = sp 3d 2 In other words, you only have to count the number of bonds or lone pairs of electrons around a central atom to determine its hybridization. Because hybridiztion is used to make atomic overlaps, knowledge of the number and types of overlaps an atom makes allows us to determine the degree of hybridization it has. One of the s orbital electrons is promoted to the open p orbital slot in the carbon electron configuration and then all four of the orbitals become "hybridized" to a uniform energy level as 1s + 3p = 4 sp 3įiguring out what the hybridization is in a molecule seems like it would be a difficult process but in actuality is quite simple. So how do we explain this? Simple: Hybridization We see a methane with four equal length and strength bonds. This means that the two p electrons will make shorter, stronger bonds than the two s electrons right? But this is not what we see.
This will be the 2s and 2p electrons for carbon.Īs you know, p electrons are of higher energy than s electrons. According to Valence Bond Theory, the electrons found in the outermost (valence) shell are the ones we will use for bonding overlaps. The Carbon in methane has the electron configuration of 1s 22s 22p 2. Let's start this discussion by talking about why we need the energy of the orbitals to be the same to overlap properly.
The process by which all of the bonding orbitals become the same in energy and bond length is called hybridization. In order to overlap, the orbitals must match each other in energy. This is what I call a "side-by-side" bond. Pi (π) Bonds form when two un-hybridized p-orbitals overlap. I often refer to this as a "head-to-head" bond. Sigma (σ) Bonds form between the two nuclei as shown above with the majority of the electron density forming in a straight line between the two nuclei. There are two different types of overlaps that occur: Sigma (σ) and Pi (π) When the bonds form, it increases the probability of finding the electrons in the space between the two nuclei. In this theory we are strictly talking about covalent bonds.Īccording to the theory, covalent (shared electron ) bonds form between the electrons in the valence orbitals of an atom by overlapping those orbitals with the valence orbitals of another atom. The Valence Bond Theory is the first of two theories that is used to describe how atoms form bonds in molecules. In this lecture we Introduce the concepts of valence bonding and hybridization. The content that follows is the substance of General Chemistry Lecture 35.
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