Chapter 13Molecular Shapes

Molecular Shape

• Molecular shape or molecular geometry is the three-dimensional arrangement of the atoms in a molecule.

Molecular Shape

• Molecular shape determines several properties of a substance including: – reactivity – polarity – phase of matter – color – magnetism – biological activity

Olfaction – sense of smell

• Lock-and-Key Theory: humans can smell various odors because each three-dimensional odor molecule fits into only one type of receptor.

Gustation – the sense of taste

• Taste receptors are located on the tongue and are sensitive to four major tastes: salty, sweet, sour and bitter.

• Taste receptors respond differentially to the varying shapes of food and liquid molecules.

H2

H H

2(1) = 2e-

Any 2 atoms

linear

What about molecules consisting of more than two atoms

Five Molecular Shapes

See the table in your notes

Steps in Determining Molecular Shape

1. Draw the Lewis Structure for the Molecule.

2. Count the number of atoms attached to the central atom.

3. Count the number of lone pairs attached to the central atom.

4. Use your counts on steps 2 and 3 to determine the shape of the molecule.

H2S

• Dihydrogen monosulfide or just hydrogen sulfide is also known as sewer gas. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs.

H HS••

••

2(1)+6 = 8e-

2/2

angular

H2S

• Dihydrogen monosulfide or just hydrogen sulfide is also known as sewer gas. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs.

H HS•• ••

Methane (CH4)4 + 4(1) = 8e-

Methane (CH4)4 + 4(1) = 8e-

4 atoms attached to the central atom.0 lone pairs on the central atom.4/0

Tetrahedral shape

Methane (CH4)4 + 4(1) = 8e-

4 atoms attached to the central atom.0 lone pairs on the central atom.4/0

Tetrahedral shape

HCN

H NC••

••

1+4+5 = 10e-

••

••

••

HCN

H NC••

••

1+4+5 = 10e-

••

••

••

HCN

H NC••

••

1+4+5 = 10e-

••

••

••

HCN

H NC••

1+4+5 = 10e-

••

••

HCN

H NC••

1+4+5 = 10e-

••

••

HCN

H NC

1+4+5 = 10e-

••

2/0

linear

H2S

H HS•• ••

2/2

angular

SO2

O OS••

••

6+2(6) = 18e-

••

••

••••

••••

SO2

O OS••

••

6+2(6) = 18e-

••

••

••••

••••

SO2

O OS••

••

6+2(6) = 18e-

••

••

••••

••••

2/1angular

CH4

4/0

tetrahedral

NO3-

O ON••

••

5+3(6)+1 = 24e-

••

••

••••

••••

O ••••

NO3-

O ON••

••

5+3(6)+1 = 24e-

••

••

••••

••••

O ••••

NO3-

O ON••

••

5+3(6)+1 = 24e-

••

••

••••

••••

O ••••

NO3-

O ON

5+3(6)+1 = 24e-

••

••

••••

••••

O •••• 3/0

trigonal planer

[ ]-

SOCl2

What’s the shape of acetate?

4/0

tetrahedral

3/0

trigonal planer

Homework

Worksheet Chapter 13.