6.4 VSEPR (Molecular Shapes)

6.4 VSEPR (Molecular Shapes)

V ValenceS ShellE ElectronP PairR Repulsion

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I hate you!Stay away from me!

VSEPR: theory that predicts some molecular shapes based on idea that pairs of valence electrons surrounding an atom repel each other

Common shapes you should know

Tetrahedral

pyramid with 4 faces

Trigonal pyramidal

squished pyramid

Trigonal Planar

hood ornament of Mercedes

peace sign missing a limb

Bent

Linear

How do we figure out the shape of a molecule?

Step 1: Draw the Lewis structure for the molecule.

example: NH3

Step 2: Count the number of "things" on the atom you're interested in (the center atom).

Count atoms and lone pairs, NOT BONDS!

example: NH3

NH

H

H

Step 3: Count the number of lone pairs that are on the atom you're interested in.

Lone pairs on other atoms aren't important;only count what is directly stuck to the atom you're interested in.

example: NH3

NH

H

H

Practice

1. CH4

2. CO2

3. carbon tetrabromide

4. phosphorus trichloride

5. boron trichloride

6. sulfur difluoride

How does shape affect polarity?

Practice: are the following molecules polar or nonpolar?

1. CF4

2. SF2

3. NF3

4. BeCl2

Drag the figure showing the shape for this molecule into the box below.

CO2

Drag the figure showing the shape for this molecule into the box below.

AsF5

Drag the figure showing the shape for this molecule into the box below.

SO3

Drag the figure showing the shape for this molecule into the box below.

NH4+

Drag the figure showing the shape for this molecule into the box below.

SCl6