Question

What is the hybridization of the central atom in (a) \(\mathrm{SiCl}_{4}\), \((\mathbf{b}) \mathrm{HCN},(\mathbf{c}) \mathrm{SO}_{3},(\mathbf{d}) \mathrm{TeCl}_{2} ?\)

Short answer

The hybridizations of the central atoms in the given compounds are: (a) SiCl₄: \(sp^3\); (b) HCN: \(sp\); (c) SO₃: \(sp^2\); and (d) TeCl₂: \(sp^3\).

Step-by-step solution

Determine the electron domain count for each central atom

For SiCl₄, the central atom Si has four single bonds (sigma bonds) with four Cl atoms, and no lone pairs. So, the electron domain count is 4. For HCN, the central atom C has one sigma bond with H, a triple bond with one sigma bond and two pi bonds with N, and no lone pairs. So, the electron domain count is 2. For SO₃, the central atom S has a resonance structure with three double bonds (one sigma bond and one pi bond each) to three O atoms, and no lone pairs. So, the electron domain count is 3. For TeCl₂, the central atom Te has two single bonds (sigma bonds) with two Cl atoms, plus two lone pairs. So, the electron domain count is 4.

Determine the hybridization based on electron domain count

For Si in SiCl₄, with an electron domain count of 4, the hybridization is sp³ (s¹p³). For C in HCN, with an electron domain count of 2, the hybridization is sp (s¹p¹). For S in SO₃, with an electron domain count of 3, the hybridization is sp² (s¹p²). For Te in TeCl₂, with an electron domain count of 4, the hybridization is sp³ (s¹p³). Now we have determined the hybridization for the central atom in each of the given compounds: (a) SiCl₄: sp³ hybridization (b) HCN: sp hybridization (c) SO₃: sp² hybridization (d) TeCl₂: sp³ hybridization

Key concepts

Electron Domain Count

The concept of electron domain count is essential for understanding molecular geometry and hybridization. Electron domains include all regions of electron density around a central atom. These could be bonds (single, double, or triple) or lone pairs of electrons.

For example:

• In SiCl₄, the silicon atom bonds with four chlorine atoms through single sigma bonds. It has no lone pairs, resulting in an electron domain count of 4.
• In HCN, the central carbon is bonded to hydrogen with a single sigma bond and to nitrogen with a triple bond, which includes one sigma and two pi bonds. No lone pairs gives an electron domain count of 2.
• SO₃ presents sulfur with three double bonds to oxygen. Again, no lone pairs means the electron domain count is 3.
• TeCl₂'s tellurium central atom is bonded to two chlorine atoms with single sigma bonds and has two additional lone pairs, resulting in an electron domain count of 4.

Understanding these counts helps predict hybridization types, as specific counts correlate with specific hybridizations, enhancing our understanding of the molecule's shape.

Central Atom

The central atom in a molecule is typically the atom with the highest capacity to form bonds, or it can be the one that is least electronegative. This atom is pivotal in determining the geometry and hybridization, as it is surrounded by electron domains

In the examples:

• Silicon (Si) in SiCl₄ is the central atom. Its four bonds shape a tetrahedral geometry.
• Carbon (C) in HCN acts as the central atom, organizing its linear shape due to minimal electron sharing regions.
• Sulfur (S) in SO₃, with resonance possibilities, forms a planar trigonal shape.
• Tellurium (Te) in TeCl₂, with two lone pairs, assumes a bent/angular structure.

The more electron domains, the more complex the geometry can become, typically affecting hybridization.

Sigma Bonds

Sigma bonds are the foundation of covalent bonding, formed by the head-on overlap of orbitals. They allow atoms to be bound together in a molecule tightly.

Here’s how sigma bonds appear in each compound:

• In SiCl₄, four sigma bonds link silicon to chlorine atoms, organizing a tetrahedral shape due to sp³ hybridization.
• With HCN, two sigma bonds are present. One links carbon to hydrogen, and the second forms part of the triple bond with nitrogen.
• SO₃’s sulfur forms three sigma bonds with each oxygen, supplemented by pi bonds due to double bonding.
• In TeCl₂, two sigma bonds exist between tellurium and the two chlorine atoms.

The number of sigma bonds is integral to determining the molecular structure and symmetry.

Resonance Structure

Resonance structures are multiple ways of drawing a Lewis structure for a molecule with conjugated bonds. They highlight the delocalization of electrons within molecules.

Focusing on SO₃, resonance structures help explain its hybridization and stabilization. Sulfur's bonds with oxygen can shuffle between double and single, redistributing electron density and preserving a consistent electron domain count.

Here's how resonance aids understanding:

• The double-bond switching within the oxygens results creates equivalent forms. It doesn’t change the overall count for hybridization.
• The concept of resonance supports stabilization, since energy minimization due to electron distribution protects molecular integrity.
• By examining resonance, predictions about molecular behavior, reactivity, and interactions become clearer.

Recognizing resonance structures illuminates the dynamic nature of electron arrangements in molecules like SO₃.