Year 12s: what will be the first way you research your future options? >>

Hybridisation and pi/sigma bonds; A Level Chemistry

Hello.
Can someone explain me hybridisation and stuff? I don't know why, but I find it very confusing.
Now, we know that when forming covalent bonds, the atomic orbitals overlap and molecular orbitals are formed. So, are the hybrids such as sp³ formed after that overlap? Or is it the atomic orbitals that form these hybrids, and later overlap with the hybrids of the other atoms?

Anyone?

Original post by Knightrises10

Hybridisation does not exist, as such. It is a model to explain the empirical observations of bond angles in simple molecular systems.

Forget the idea of a "process".

There are atoms, that have atomic orbitals, as emerge from the solutions to Schroedinger's equation and ...

There are molecules in, which there is more than one nuclear centre and hence regions of space in which the electrons have a 99% probability of being found (molecular orbitals). Were it possible to solve Schroedinger's equation for multi-centre particles (molecules) then the shapes would emerge from the solutions in just the same way.

The only evidence we have for the shape of molecular orbitals is the shape of the molecules and bond lengths. We observe that methane is tetrahedral and so it stands to reason that the molecular orbitals are arranged tetrahedrally. Hybridisation is a MODEL to allow us to give a logical explanation of this.

We know that carbon has an outer configuration of 2s² 2p². The orbital orientation and occupation could not overlap with hydrogen orbitals to give a tetrahedral shape. So we INVENT a process whereby we say that the atomic orbitals mix and reform and we call it hybridisation, in order to have degenerate orbitals that can overlap with hydrogen 1s orbitals.

The carbon electronic arrangement 2s² 2p² becomes four hybridised orbitals designated sp³. These can then overlap with the correct tetrahedral orientation to form methane.

The whole idea is a MODEL. It is not intended to give a story of how it actually happens. Methane is a multi-nuclear centre particle with its own solutions to Schroedinger's equation, and those solutions are tetrahedrally orientated.

The utility of a model is that it gives the correct results. In period 3 the elements do not produce molecules that fit well with the model. Hybridisation fails to explain hydrogen sulfide, for example.

However, it is a good model for bonding in carbon compounds and molecules formed by period 2 elements.