CH08.4.2 VSEPR Model and Molecular Shape

The shapes of the molecules shown have been determined by means of the VSEPR model. What is the basic assumption of this model?

• Electron pairs in the valence shell of an atom attract each other and try to get as close as possible.
• Electron pairs in the valence shell of an atom have no effect on each other.
• Electron pairs in the valence shell of an atom repel each other and try to stay close together.
• Electron pairs in the valence shell of an atom repel each other and try to get as far apart as possible.

There are no lone pairs and _ shared pairs of electrons surrounding the boron atom in the borane (BH₃) molecule shown.

• 4

• 2

• 3

• 1

Answer explanation

Covalent bonds are formed by shared pairs of electrons. Each bond is made of two shared electrons, typically each electron in the shared pair comes from each atom bonded.

What is the shape of the BH₃ molecule?

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• 
• 
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How many lone pairs and how many shared pairs of electrons surround the carbon atom in methane (CH₄)?

• 2 shared pairs, 2 lone pairs
• 3 shared pairs, 1 lone pair
• 1 shared pair, 3 lone pairs
• 4 shared pairs, 0 lone pairs

What is the shape of the methane molecule?

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• 
• 
• 

How many lone pairs and how many shared pairs of electrons surround the nitrogen atom in ammonia (NH₃)?

• 1 shared pair and 3 lone pairs
• 2 shared pairs and 2 lone pairs
• 3 shared pairs and 1 lone pair
• 4 shared pairs and 0 lone pairs

What is the shape of the ammonia molecule?

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• 
• 
• 

How many lone pairs and how many shared pairs of electrons surround the oxygen atom in water (H₂O)?

• 1 lone pair and 3 shared pairs
• 3 lone pairs and 1 shared pair
• 4 lone pairs and 0 shared pairs
• 2 lone pairs and 2 shared pairs

What is the shape of the water molecule?

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• 
• 
• 

How many lone pairs and how many shared pairs of electrons surround the fluorine atom in the hydrofluoric acid?

• 3 lone pairs and 1 shared pair
• 4 lone pairs and 0 shared pairs
• 1 lone pair and 3 shared pairs
• 2 lone pairs and 2 shared pairs