Transcript Molecular Shape - Wappingers Central School District

Molecular Shape
VSEPR Model
Molecular Shape
Physical/Chemical PROPERTIES
SHAPE of Molecule (VSEPR)
Overlap of ORBITALS (Hybridization)
VSEPR Model

Lewis Structure used to determine the
molecular geometry or shape.
– Model used is called Valence Shell Electron Pair
Repulsion model

VSEPR – based on arrangement that
minimizes the repulsion of shared and
unshared pairs of electrons around the
central atom.
Predicting Shapes

Start with Lewis Dot structure
– Show both bonding/nonbonding pairs e– Note that double and triple bonds are
viewed as single bonds of e- density.
Predicting Shapes
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2
3
4
5
6
pairs
pairs
pairs
pairs
pairs
Comparisons
eeeee-
LINEAR
TRIGONAL PLANAR
TETRAHEDRAL
TRIGONAL BIPYRAMIDAL
OCTAHEDRAL
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/VSEPR.swf
Molecular Shapes (routine)
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Draw Lewis Structure
– Focus on central atom

Count up the regions of electron
density on central atom
– i.e., bonding and nonbonding pairs
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Count up the number of atoms bonded
to the central atom
Assign Numbers…
electron density, atoms bonded
Molecule
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CO2
CH4
NH3
H2O
Shape
2,2
4,4
4,3
4,2
linear
tetrahedral
pyramid
bent
Bond Angle
180o
109o
107o
105o
Molecular Geometry

Examples
http://www.uwosh.edu/faculty_staff/xie/tutorial/vsepr.htm#live
Hybridization

Mixing of two or more atomic orbitals
of similar energies on the same atom
to give new orbitals or equal energies.
– Special types of atomic orbitals that have
energy intermediate between s and p
orbitals.
Animation
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf
More…
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom5s2_6.swf
sp3 Hybridizaiton
Energy of sp3 Orbitals
The 2s electron is promoted to the 2pz orbital and the four
orbitals then undergo hybridization to form four degenerate
orbitals. As these new orbital have emerged from one s and
three p orbitals they are called 'sp3' orbitals.
Ammonia
bonding electrons in a probability area for the hybrid orbital...
Geometry of Hybrid Orbitals
Atomic
Orbitals
s, p
Type of
Hybrid
Number
of Hybrid
Geometry
sp
2
Linear
(e- pairs)
s, p, p
s, p, p, p
sp2
sp3
3
(e- pairs)
Trigonal
Planar
4
Tetrahedral
(e- pairs)
Molecular Orbitals

Sigma Bonds (s)
– Two atomic orbitals combine to form a molecular
orbital that is symmetricl around the axis
connecting nuclei.
Sigma Bonds
Molecular Orbitals

Pi Bonds (p)
– Side-by-side overlap of two p atomic orbitals
produces a pi-bonding molecular orbital.
– Atomic orbitals overlap less than in sigma bonding
so pi (p) bonds tend to be weaker.
Hybridization and
Multiple Bonds

Maximum of two electrons per orbital
– So multiple bonds must include sigma (s)
and pi (p) bonds.
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Double Bonds  One s and one p
Triple Bonds  One s and two p
Formation of Sigma and Pi
molecular orbitals
Molecular Orbitals
Correlation Diagram