Molecular ShapeMolecular Shape

Pp 259-262Pp 259-262

VSEPR TheoryVSEPR Theory

Valence Shell Electron Pair RepulsionValence Shell Electron Pair Repulsion Used to determine molecular shapeUsed to determine molecular shape Based on arrangement that Based on arrangement that

minimizes the repulsion between minimizes the repulsion between shared and unshared electronsshared and unshared electrons

Bond AngleBond Angle

Angle formed by any two terminal Angle formed by any two terminal atoms and a central atomatoms and a central atom

Caused by the repulsion of electron Caused by the repulsion of electron pairspairs

Supported by experimental evidenceSupported by experimental evidence Shared electron pairs repel each Shared electron pairs repel each

otherother

Lone pairs and VSEPRLone pairs and VSEPR

Lone pairs also importantLone pairs also important Occupy a larger orbital than shared Occupy a larger orbital than shared

electronselectrons Lone pairs push shared orbitals Lone pairs push shared orbitals

togethertogether

VSEPR DefinitionsVSEPR Definitions

• Electron groupElectron group –set of electrons that –set of electrons that occupies a particular region around an occupies a particular region around an atom.atom.

• LigandLigand – an atom or a group of atoms – an atom or a group of atoms bonded to an inner atombonded to an inner atom

• Steric numberSteric number – the sum of the number – the sum of the number of ligands plus the number of lone pairs; of ligands plus the number of lone pairs; in other words, the total number of in other words, the total number of groups associated with that atom.groups associated with that atom.

LinearLinear 180’180’

Bent/angularBent/angular <120’<120’

Bent/angularBent/angular 104.5104.5

Trigonal Trigonal planarplanar

120’120’ TetrahedralTetrahedral 109.5’109.5’

Trigonal Trigonal pyramidalpyramidal

107.3’107.3’

Trigonal bipyramidalTrigonal bipyramidal 90’ Horz to vert90’ Horz to vert 120’ horz to horz120’ horz to horz

OctahedralOctahedral 90’90’

See-sawSee-saw

Square planarSquare planar

T-structureT-structure LinearLinear

Square pyramidalSquare pyramidal

HybridizationHybridization What’s a hybrid?What’s a hybrid?

• Combining two of the same type of object and contains Combining two of the same type of object and contains characteristics of bothcharacteristics of both

Occurs to orbitals during bondingOccurs to orbitals during bonding HybridizationHybridization

• Process in which atomic orbitals are mixed to form new Process in which atomic orbitals are mixed to form new hybrid orbitalshybrid orbitals

• Each hybrid orbital contains one electron that it can Each hybrid orbital contains one electron that it can share with another atomshare with another atom

Carbon is most common atom to undergo Carbon is most common atom to undergo hybridizationhybridization• Four hybrid orbitals from 1 s and 3 p orbitalsFour hybrid orbitals from 1 s and 3 p orbitals• Hybrid= spHybrid= sp33 orbital orbital

HYBRIDIZATIONHYBRIDIZATION

Mixture of two or Mixture of two or more atomic more atomic orbitals of similar orbitals of similar energies on the energies on the same atom to same atom to produce new produce new hybrid atomic hybrid atomic orbitals of equal orbitals of equal energiesenergies

Orbitals of equal Orbitals of equal energy produced energy produced by the combination by the combination of two or more of two or more orbitals on the orbitals on the same atomsame atom

Hybrid OrbitalHybrid Orbital

# of atomic orbitals mixed to form hybrid orbitals = # of atomic orbitals mixed to form hybrid orbitals = the total # of pairs of shared electronsthe total # of pairs of shared electrons

# of hybrid orbitals formed = # of atomic orbitals # of hybrid orbitals formed = # of atomic orbitals mixedmixed• 1 s orbital + px + py + pz = 4 sp1 s orbital + px + py + pz = 4 sp33 hybrid orbitals hybrid orbitals

CHCH44

AlClAlCl33 Lone pairs also occupy hybrid orbitalsLone pairs also occupy hybrid orbitals

• HH22OO

• BeClBeCl22

Class WorkClass Work

Lewis Dot Diagram Lewis Dot Diagram (6 steps)(6 steps)

Molecular Molecular geometrygeometry

Bond AngleBond Angle Type of Type of

hybridizationhybridization New Lewis dot New Lewis dot

structure showing structure showing molecular shapemolecular shape

1.1. BFBF33

2.2. NHNH44++

3.3. OClOCl224.4. BeFBeF22

5.5. CFCF44

6.6. AsHAsH33