Question 9.5: Describe the orbital hybridization around the central atom i...
Describe the orbital hybridization around the central atom in NH^{-}_{2}.
Analyze We are given the chemical formula for a polyatomic anion and asked to describe the type of hybrid orbitals surrounding the central atom.
Plan To determine the central atom hybrid orbitals, we must know the electron-domain geometry around the atom. Thus, we draw the Lewis structure to determine the number of electron domains around the central atom. The hybridization conforms to the number and geometry of electron domains around the central atom as predicted by the VSEPR model.
Solve The Lewis structure is
\left[H \overset{\cdot \cdot }{\underset{\cdot \cdot }{:N:}} H\right]^{-}
Because there are four electron domains around N, the electrondomain geometry is tetrahedral. The hybridization that gives a tetrahedral electron-domain geometry is sp^{3} (Table 9.4). Two of the sp^{3} hybrid orbitals contain nonbonding pairs of electrons, and the other two are used to make bonds with the hydrogen atoms.
| TABLE 9.4 Geometric Arrangements Characteristic of Hybrid Orbital Sets | |||
| Atomic Orbital Set | Hybrid Orbital Set | Geometry | Examples |
| s,p | Two sp |  |
BeF2, HgCl2 |
| s,p,p | Three sp^{2} |  |
BF3, SO3 |
| s,p,p,p | Four sp^{3} |  |
CH4, NH3, H2O, NH{+}4 |