lecture 8.3- vsepr

BellworkPipe cleaner shapes

# of “legs” picture name

2

3

4

The Valence-shell electron-pair repulsion (VSEPR) Model states that electron pairs in a molecule will be as far apart as they

can be because they repel each other.

Linear

Trigonal planar Tetrahedral

An electron domain is an area around an atom where electrons are found.

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An electron domain is an area around an atom where electrons are found.

They can be bonding or non-bonding (lone pairs).

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An electron domain is an area around an atom where electrons are found.

They can be bonding or non-bonding (lone pairs).

Bonding domains can contain two, four, or six e-.

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The number of electron domains determines the electron-domain geometry.

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The number of electron domains determines the electron-domain geometry.

The number of lone pairs determines the final shape of the molecule.

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The hydrogens in a methane molecule are at the four corners of a tetrahedron.

The bond angles are 109.5°.

The measured H—N—H bond angle in ammonia is only 107°.

The measured bond angle in water is about 105°.

Lone Pair

Bonding Pair

Lone pairs repel more than bonding electrons

Water’s bond angle is 104.5° (much less than the tetrahedral

angle of 109.5°) because its lone pairs need extra room.

A carbon dioxide molecule is linear.

Nine Possible Molecular Shapes

VSEPR theory enables prediction of 3-dimensional molecular shape because the valence electron pairs

a)are attracted to each other.

b)form molecules with only four possible shapes.

c)stay as far apart as possible.

d)always form tetrahedral shapes.

Bellwork- VSEPR Theory Fill in the missing information

moleculeLewis

structure

# of e-

domains (bonding

areas) picture name

methane CH4

ammonia NH3

water H2O

Bellwork- VSEPR Theory Fill in the missing information

moleculeLewis

structure

# of e-

domains (bonding

areas) picture name

methane CH4

4

ammonia NH3

4

water H2O

4

Bellwork- VSEPR Theory Fill in the missing information

moleculeLewis

structure

# of e-

domains (bonding

areas) picture name

methane CH4

4 tetrahedral

ammonia NH3

4trigonal

pyramidal

water H2O

4 bent