Chapter 6: Shapes of molecules & IMF

Question 1

What is electron pair repulsion theory?

Answer 1

Electron pairs around a nucleus repel such that the structure of these pairs around the nucleus minimises repulsion.

Question 2

By how much do lone pairs reduce bond angle?

Answer 2

2.5° for each lone pair around the nucleus

Question 3

What are the 4 main types of shape with their corresponding number of electron dense regions.

Answer 3

Linear- 2
Trigonal Planar- 3
Tetrahedral- 4
Octahedral- 6

Question 4

What are the bond angles of molecule shapes when there are no lone pairs?

Answer 4

Linear- 180°
Trigonal Planar- 120°
Tetrahedral- 109.5°
Octahedral- 90°

Question 5

Do double or triple bonds affect bond angle?

Answer 5

No

Question 6

Can electron pair repulsion theory be used on ions?

Answer 6

Yes

Question 7

What is polarity?

Answer 7

When one nucleus out of a bonded pair exerts a greater attractive force on the bonding electrons such that a permanent dipole is produced.

Question 8

What is electronegativity?

Answer 8

The attraction of a bonded atom for the pair of bonded electrons in a covalent bond.

Question 9

How does electronegativity vary on the periodic table and why?

Answer 9

Increases across a period due to increased nuclear charge and reduced atomic radius,
Decrease down a group as atomic radius increase and shielding by electrons also increases.

Question 10

How do you use electronegativity to determine a bond?

Answer 10

Evaluate the difference in electronegativity in bonded atoms:
0- Nonpolar
0 to 1.8- Polar
greater than 1.8- Ionic

Question 11

What is a pure covalent bond?

Answer 11

A covalent bond where the bonding atoms are of the same element; hence diatomic molecules usually.

Question 12

What is a nonpolar bond?

Answer 12

A bond where the electron pair is equally shared between each bonding atom.

Question 13

What is polar bond

Answer 13

A bond where electronegativity differs such that the electron pair are not equally shared.

Question 14

When is a molecule polar?

Answer 14

When a molecule contains polar bonds arrange asymmetrically such that they do not cancel.

Question 15

What is a polar solvent?

Answer 15

A solvent which itself is polar and thus contains polar bonds.

Question 16

What are the three types of intermolecular forces?

Answer 16

• Induced dipole-dipole interactions (London forces)
• Permanent dipole-dipole interactions
• Hydrogen bonding

Question 17

What are induced dipole-dipole interactions (London Forces)?

Answer 17

Weak intermolecular forces which exist between all molecules. Caused by small fluctuations in the electron cloud around one molecule inducing an instantaneous dipole around neighboring molecules; radiating this effect out.

Question 18

What are permanent dipole-dipole interactions?

Answer 18

A force arising from the electrostatic attraction of dipoles between polar molecules.

Question 19

How do you increase the strength of London forces?

Answer 19

Greater attraction is felt by molecules with a greater number of electrons as the induced dipole becomes more significant (greater instantaneous polarity).

Question 20

What is the structure of a solid molecule?

Answer 20

A simple Molecular Lattice.

Question 21

What types of solvents pull polar and nonpolar molecules into solution?

Answer 21

Nonpolar solvents for nonpolar molecules

Polar solvent for polar molecules.

Question 22

Why in solvents do like dissolve like?

Answer 22

As an intermolecular force needs to be overcome, induced dipoles and can overcome other induced dipoles but not permanent dipoles. Hence permanent can overcome permanent.

Question 23

Can covalent molecules conduct?

Answer 23

No, no charge carriers.

Question 24

What is hydrogen bonding?

Answer 24

A type of permanent dipole dipole interaction occurring between H-O H-N H-F. Where the polar hydrogen strongly attracts the lone pair around the O, N, F of other molecules.

Question 25

Why is water anomalous?

Answer 25

Utilises hydrogen bonding to have a higher than expected boiling point and also has quite high surface tension.

Question 26

Arrange the types of IMF in terms of strength smallest first.

Answer 26

• London Forces
• Permanent dipole dipole interactions
• Hydrogen bonding