Determine orbital hybridization from molecular geometry and bonding
Hybridization is the mixing of atomic orbitals to form new hybrid orbitals suitable for bonding. The type of hybridization depends on the steric number (bonding pairs + lone pairs).
Steric Number 2: sp (linear, 180°)
Steric Number 3: sp² (trigonal planar, 120°)
Steric Number 4: sp³ (tetrahedral, 109.5°)
Steric Number 5: sp³d (trigonal bipyramidal, 90°/120°/180°)
Steric Number 6: sp³d² (octahedral, 90°/180°)
Key: Lone pairs affect molecular geometry but not hybridization. For example, H₂O has sp³ hybridization (like CH₄) but bent geometry due to 2 lone pairs.
Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons in chemical bonding. This theory explains the bonding, molecular shapes, and properties of molecules.
When atoms bond, their atomic orbitals (s, p, d) mix to form hybrid orbitals that are identical in shape and energy. The number and type of hybrid orbitals formed depends on the number of electron groups around the central atom.
Key Concept:
The steric number (bonding pairs + lone pairs) determines the hybridization type. Steric number 2 = sp, 3 = sp², 4 = sp³, 5 = sp³d, 6 = sp³d².
Orbitals Mixed: 1 s + 1 p = 2 sp orbitals
Steric Number: 2
Geometry: Linear
Bond Angle: 180°
Unused p Orbitals: 2 (available for π bonds)
Common Examples:
Orbitals Mixed: 1 s + 2 p = 3 sp² orbitals
Steric Number: 3
Geometry: Trigonal Planar
Bond Angle: 120°
Unused p Orbitals: 1 (available for π bonds)
Common Examples:
Orbitals Mixed: 1 s + 3 p = 4 sp³ orbitals
Steric Number: 4
Geometry: Tetrahedral
Bond Angle: 109.5°
Unused p Orbitals: 0 (only σ bonds)
Common Examples:
Orbitals Mixed: 1 s + 3 p + 1 d = 5 sp³d orbitals
Steric Number: 5
Geometry: Trigonal Bipyramidal
Bond Angles: 90°, 120°, 180°
Note: Requires 3rd period or higher (d orbitals)
Common Examples:
Orbitals Mixed: 1 s + 3 p + 2 d = 6 sp³d² orbitals
Steric Number: 6
Geometry: Octahedral
Bond Angles: 90°, 180°
Note: Requires 3rd period or higher (d orbitals)
Common Examples:
Determine the hybridization of the nitrogen atom in ammonia (NH₃).
Step 1: Determine the Lewis Structure
Nitrogen has 5 valence electrons, each hydrogen has 1.
N: 5 electrons | H: 3 × 1 = 3 electrons | Total = 8 electrons
Structure: N-H bonds (3 bonding pairs) + 1 lone pair on N
Step 2: Count Electron Groups (Steric Number)
Bonding pairs: 3 (N-H bonds)
Lone pairs: 1 (on nitrogen)
Steric Number = 3 + 1 = 4
Step 3: Determine Hybridization
Steric number of 4 corresponds to sp³ hybridization
The nitrogen atom mixes 1 s orbital and 3 p orbitals to form 4 sp³ hybrid orbitals.
Step 4: Determine Geometry
Electron Geometry: Tetrahedral (4 electron groups)
Molecular Geometry: Trigonal Pyramidal (3 atoms + 1 LP)
Bond Angle: ~107° (less than 109.5° due to LP repulsion)
Answer:
The nitrogen atom in NH₃ is sp³ hybridized with a trigonal pyramidal molecular geometry and bond angles of approximately 107°.
VSEPR (Valence Shell Electron Pair Repulsion) theory states that electron pairs around a central atom arrange themselves to minimize repulsion. This arrangement determines both the hybridization and molecular geometry.
| Steric Number | Hybridization | Electron Geometry | Bond Angle |
|---|---|---|---|
| 2 | sp | Linear | 180° |
| 3 | sp² | Trigonal Planar | 120° |
| 4 | sp³ | Tetrahedral | 109.5° |
| 5 | sp³d | Trigonal Bipyramidal | 90°, 120°, 180° |
| 6 | sp³d² | Octahedral | 90°, 180° |
Important Note:
Lone pairs affect molecular geometry but NOT hybridization. For example, CH₄, NH₃, and H₂O all have sp³ hybridization (4 electron groups), but different molecular shapes: tetrahedral, trigonal pyramidal, and bent, respectively.
Understanding carbon hybridization (sp, sp², sp³) is crucial for predicting molecular shapes, reactivity, and properties of organic compounds. Different hybridization states explain why alkanes, alkenes, and alkynes have different geometries and reactivities.
Pharmaceutical chemists use hybridization to design drugs that fit specific enzyme active sites. The 3D shape of molecules (determined by hybridization) affects how drugs bind to target proteins.
Diamond (sp³ carbon) and graphite (sp² carbon) have dramatically different properties due to different hybridization. This knowledge helps design new materials with specific properties.
Protein and DNA structures depend on the hybridization of atoms in amino acids and nucleotides. Understanding hybridization helps explain enzyme mechanisms and genetic coding.
Hybridization affects molecular orbital energy levels, influencing UV-Vis and IR spectra. This allows chemists to identify unknown compounds and study molecular structure.
Metal complexes use d²sp³ or sp³d² hybridization for octahedral geometry, crucial for catalysis, biological systems (hemoglobin), and industrial processes.
A double or triple bond counts as ONE electron group, not two or three.
Correct: CO₂ has 2 electron groups (2 double bonds), not 4
Hybridization determines electron geometry. Lone pairs affect molecular shape.
Correct: H₂O is sp³ (electron geometry: tetrahedral) but bent (molecular geometry)
sp³d and sp³d² require d orbitals, only available from period 3 onward.
Correct: PCl₅ (P in period 3) can be sp³d, but NCl₅ doesn't exist (N in period 2)
Lone pairs count toward the steric number and affect hybridization.
Correct: Include lone pairs when calculating steric number
SN = BP + LP
Steric Number determines hybridization
SN=2: sp, Linear, 180°
SN=3: sp², Trigonal planar, 120°
SN=4: sp³, Tetrahedral, 109.5°
SN=5: sp³d, Trig. bipyramidal, 90°/120°/180°
SN=6: sp³d², Octahedral, 90°/180°
sp = 1s + 1p (2 orbitals)
sp² = 1s + 2p (3 orbitals)
sp³ = 1s + 3p (4 orbitals)
sp³d = 1s + 3p + 1d (5 orbitals)
sp³d² = 1s + 3p + 2d (6 orbitals)
2: "sp is simple" (linear)
3: "sp² is a triangle" (trig. planar)
4: "sp³ is a tetrahedron"
5: "sp³d has 5 points"
6: "sp³d² is a 6-sided die"