Hybridization in Methane, Ammonia, and Water

What orbitals are available to make the four identical C-H bonds in methane The four hydrogen atoms provide four Is orbitals. The configuration of elemental carbon can be written as 

we promote one electron from the 2s to the 2p orbital to give 

Ammonia and water also have structures based on sp hybridization at the central atom. We know that ammonia is a base and that it has a nonbonding or lone pair of electrons. The electronic configuration of nitrogen is 

Moving on to water, oxygen has the following electronic configuration  

FIGURE 2.3 Paired and unpaired electrons in the sp orbitals of nitrogen in ammonia. 

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