![]() ![]() The bonds that form by the head-on overlap of orbitals are called σ (sigma) bonds because the electron density is concentrated on the axis connecting the C and H atoms. The four sp 3-hybridized orbitals arrange in a tetrahedral geometry and make bonds by overlapping with the s orbitals of four hydrogens: This explains the symmetrical geometry of methane (CH 4) where all the bonds have the same length and bond angle.Īll four C – H bonds in methane are single bonds that are formed by head-on (or end on) overlapping of sp 3 orbitals of the carbon and s orbital of each hydrogen. The formation of these degenerate hybrid orbitals compensates for the energy uphill of the s-p transition as they have lower energy than the p orbitals. And again, we call them sp 3 because they are formed from one s orbital and three p orbitals. These are hybrid orbitals and look somewhat like the s and p orbitals. ![]() So, four orbitals (one 2s + three 2p) are mixed and the result is four sp 3orbitals. The number of the hybrid orbitals is always the same as the number of orbitals that are mixed. So, in the next step, the s and p orbitals of the excited state carbon are hybridized to form four identical in size, shape, and energy orbitals. Pay attention that the electron goes uphill as the p subshell is higher in energy than the s subshell and this is not energetically favorable, but we will see how it is compensated in the next step when orbitals are mixed (hybridized). ![]() This leads to the excited state of the carbon: In the first step, one electron jumps from the 2s to the 2p orbital. Now, let’s see how that happens by looking at methane as an example. Hybridization is a theory that is used to explain certain molecular geometries that would have not been possible otherwise. And this is where we get into the need for a theory that can help us explain the known geometry and valency of the carbon atom in many organic molecules. You can see from the electron configuration that it is impossible to make four, identical in bond length, energy, and everything else (degenerate) bonds because one of the orbitals is a spherical s, and the other three are p orbitals. The valence electrons are the ones in the 2s and 2p orbitals and these are the ones that participate in bonding and chemical reactions. So, in order to predict the valency and geometry of the carbon atom, we are going to look at its electron configuration and the orbitals. Remember also that covalent bonds form as a result of orbital overlapping and sharing two electrons between the atoms. A reminder that in tetrahedral geometry, all the angles are 109.5 o and the bonds have identical lengths. It is confirmed experimentally that the carbon atom in methane (CH 4) and other alkanes has a tetrahedral geometry. Let’s start first by answering this question: Why do we need the hybridization theory? ![]()
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