Molecular Geometry

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Unit: Chemical Bonding

Molecular Geometry

Day 4 -
Notes

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After today, you should be able to…

• Explain Valence Shell Electron Pair

Repulsion Theory (VSEPRT)

• Use structural formulas to describe the

molecular geometry of molecules

• Identify the correct geometric name for

the shape of the molecule

• Identify approximate bond angles for

molecules

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Molecular Geometry

• Valence Shell Electron Pair

Repulsion Theory (VSEPR):The
electron pairs (both shared and
unshared) in the outermost energy
level try to get as far apart from
each other as possible.
–This determines the
shape of the molecule.

Multiple Choice

What does VSEPR theory determine?

• 
  The strength of covalent bonds in a molecule

• 
  The shape of the molecule based on the arrangement of electron pairs

• The color of the molecule under different light

• The number of valence electrons in a molecule

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Shape: Linear

2 atoms

– Example: H2

3 atoms

– Example: CO2

Central atom must have

NO unshared pairs

H

H

O

C

O

~180˚

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Shape: Bent

3 atoms

– Example: H2O

Central atom can have
one or two unshared

pairs of electrons

O

H

H

~104.5˚

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Shape: Trigonal Planar

4 atoms

– Example: CH2O

Central atom has
NO unshared pairs

C

O

H H

~120˚

Multiple Choice

What is the molecular geometry of a molecule with 3 atoms and no unshared pairs of electrons on the central atom?

• 
  Linear

• Bent

• Trigonal Planar

• Pyramid

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Shape: Pyramid

4 atoms

– Example: NH3

Central atom has
one unshared pair

N

H

~107.5˚

H

H

Multiple Choice

What is the molecular geometry of a molecule with 4 atoms and one unshared pair of electrons on the central atom?

• 
  Trigonal Bipyramidal

• Tetrahedral

• Pyramid

• Trigonal Planar

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Shape: Tetrahedral

5 atoms

– Example: CH4

Central atom has
NO unshared pairs

H

~109.5˚

H

C

H

H

Multiple Choice

What is the approximate bond angle in a molecule with a tetrahedral shape?

• 90 degrees
• 120 degrees
• 109.5 degrees
• 180 degrees

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Shape: Trigonal Bipyramidal

• 6 atoms

– Example: PF5

Central atom has
NO unshared pairs

For elements in period 3 and

higher, when bonded to Cl or F,

will have an expanded octet.

P


F

F

F

F

~90˚

~120˚

F

Multiple Choice

For elements in period 3 and higher, when bonded to Cl or F, they will have an expanded octet. What is the molecular geometry for such molecules?

• Trigonal bipyramidal

• Tetrahedral
• Trigonal planar
• Linear

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Summary of Shapes

Linear

Bent

Trigonal planar

Pyramid

Tetrahedral

Trigonal bipyramidal