Understanding Hybridization and Steric Number

Hybridization is a concept used in chemistry to explain the bonding in molecules where atomic orbitals mix to form new hybrid orbitals. The type of hybridization around a central atom can often be determined by calculating its steric number. The steric number is the sum of the number of sigma bonds formed by the central atom and the number of lone pairs of electrons present on the central atom.

The relationship between steric number and hybridization is as follows:

• Steric number 2: sp hybridization
• Steric number 3: sp² hybridization
• Steric number 4: sp³ hybridization
• Steric number 5: sp³d hybridization
• Steric number 6: sp³d² hybridization
• Steric number 7: sp³d³ hybridization

Determining Hybridization for Each Option

Let's calculate the steric number for the central atom in each given species:

1. $\text{NH}_4^+$

The central atom is Nitrogen ($\text{N}$).

• Valence electrons on $\text{N} = 5$.
• Number of surrounding atoms ($\text{H}$) forming sigma bonds = 4.
• Charge on the ion = +1. This means one electron is removed from the valence shell count for calculation purposes.
• Effective valence electrons for calculation = $5 - 1 = 4$.
• Number of electrons used in forming 4 sigma bonds with $\text{H}$ atoms = $4 \times 1 = 4$.
• Number of remaining valence electrons on $\text{N} = 4 - 4 = 0$.
• Number of lone pairs on $\text{N} = 0 / 2 = 0$.
• Number of sigma bonds = 4.
• Steric Number = Number of sigma bonds + Number of lone pairs = $4 + 0 = 4$.
• Hybridization for steric number 4 is sp³.

2. $\text{SF}_4$

The central atom is Sulfur ($\text{S}$).

• Valence electrons on $\text{S} = 6$.
• Number of surrounding atoms ($\text{F}$) forming sigma bonds = 4 (each $\text{F}$ forms a single bond).
• Number of electrons used in forming 4 sigma bonds with $\text{F}$ atoms = $4 \times 1 = 4$.
• Number of remaining valence electrons on $\text{S} = 6 - 4 = 2$.
• Number of lone pairs on $\text{S} = 2 / 2 = 1$.
• Number of sigma bonds = 4.
• Steric Number = Number of sigma bonds + Number of lone pairs = $4 + 1 = 5$.
• Hybridization for steric number 5 is sp³d.

3. $\text{XeF}_4$

The central atom is Xenon ($\text{Xe}$).

• Valence electrons on $\text{Xe} = 8$.
• Number of surrounding atoms ($\text{F}$) forming sigma bonds = 4 (each $\text{F}$ forms a single bond).
• Number of electrons used in forming 4 sigma bonds with $\text{F}$ atoms = $4 \times 1 = 4$.
• Number of remaining valence electrons on $\text{Xe} = 8 - 4 = 4$.
• Number of lone pairs on $\text{Xe} = 4 / 2 = 2$.
• Number of sigma bonds = 4.
• Steric Number = Number of sigma bonds + Number of lone pairs = $4 + 2 = 6$.
• Hybridization for steric number 6 is sp³d².

4. $\text{XeOF}_4$

The central atom is Xenon ($\text{Xe}$).

• Valence electrons on $\text{Xe} = 8$.
• Surrounding atoms are 4 $\text{F}$ and 1 $\text{O}$.
• $\text{Xe}$ forms 4 sigma bonds with $\text{F}$ atoms.
• $\text{Xe}$ forms 1 sigma bond and 1 pi bond with the $\text{O}$ atom (assuming a double bond). For hybridization calculation, we count only sigma bonds.
• Total number of sigma bonds = 4 (to $\text{F}$) + 1 (to $\text{O}$) = 5.
• Electrons used by $\text{Xe}$ in bonding: 4 electrons for single bonds to $\text{F}$, and 2 electrons for the double bond to $\text{O}$. Total used = $4 + 2 = 6$.
• Number of remaining valence electrons on $\text{Xe} = 8 - 6 = 2$.
• Number of lone pairs on $\text{Xe} = 2 / 2 = 1$.
• Number of sigma bonds = 5.
• Steric Number = Number of sigma bonds + Number of lone pairs = $5 + 1 = 6$.
• Hybridization for steric number 6 is sp³d².

Summary of Hybridization

Based on the calculations, the molecule with sp³d hybridization is $\text{SF}_4$.