Lewis structure promoted configurations

We can now apply the same kind of analysis to the methane molecule (CH4). The Lewis structure of CH4 has four electron domains around the central caibon atom. Tnis means that we need four hybrid orbitals, which in turn means that four atomic orbitals must be hybridized. The ground-state electron configuration of the C atom contains two unpaired electrons. Promotion of one electron from the 2s orbital to the empty 2p orbital yields the four unpaired electrons needed for the formation of four bonds ... 

The formal 2e-promotion in the n system can be represented by the configurational and Lewis structural changes shown in Fig. 5.3. As shown in the figure, ( c) ( co) NBO delocalization corresponds to formal breaking of the Jico bond [because nco) i co) with zero net bond order, is equivalent to... 

---