CHM 124 Lecture Notes - Lecture 2: Ethane, Sigma Bond, Covalent Bond
Document Summary
The simple view of the bonding in methane. You will be familiar with drawing methane using dots and crosses diagrams, but it is worth looking at its structure a bit more closely. There is a serious mis-match between this structure and the modern electronic structure of carbon, The modern structure shows that there are only 2 unpaired electrons to share with hydrogens, instead of the 4 which the simple view requires. You can see this more readily using the electrons-in-boxes notation. The 1s2 electrons are too deep inside the atom to be involved in bonding. The only electrons directly available for sharing are the 2p electrons. When bonds are formed, energy is released and the system becomes more stable. If carbon forms 4 bonds rather than 2, twice as much energy is released and so the resulting molecule becomes even more stable. The extra energy released when the bonds form more than compensates for the initial input.
