Chapter 6: Shapes of molecules and intermolecular forces (6.1, 6.2)

Question 1

what are the three types of intermolecular forces (weakest to strongest)

Answer 1

induced dipole-dipole interactions (London forces)
permanent dipole-dipole interactions
hydrogen bonding

Question 2

how do induced dipole-dipole interactions (London forces) come about

Answer 2

• movement of electrons means there will be an uneven distribution of electrons
• this creates an instantaneous dipole
• induces/causes dipoles in neighbouring molecule

Question 3

4 bonded pairs, 0 lone pairs

Answer 3

tetrahedral

109.5 degree bond angle

Question 4

3 bonded pairs, 1 lone pair

Answer 4

pyramidal

107 degree bond angle

Question 5

2 bonded pairs, 2 lone pairs

Answer 5

non linear

104.5 degree bond angle

Question 6

2 bonding regions

Answer 6

linear

180 degree bond angle

Question 7

3 bonded pairs, no lone pairs

Answer 7

trigonal planar

120 degree bond angle

Question 8

6 bonded pairs, no lone pairs

Answer 8

octahedral

90 degree bond angle

Question 9

factors that effect electronegativity

Answer 9

different nuclear charges (high nuclear charge means high electronegativity)
atoms may be different sizes (low atomic radius means high electronegativity)
one shared pair of electrons may be closer to one nucleus than the other (closer means high electronegativity)

Question 10

electronegativity trends in the periodic table

Answer 10

electronegativity increases up and along (right) the periodic table

Question 11

polar bonds

Answer 11

the bonded electron pair is attracted more to one of the bonded atoms than the other because it is more electronegative

Question 12

What effects the strength of induced dipole-dipole interactions?

Answer 12

More electrons, larger instantaneous and induced dipoles, the greater the induced dipole, dipole interaction and the stronger the attractive forces between molecules.

Question 13

Why is the boiling point of a polar substance larger than a non polar substance with the same number of electrons.

Answer 13

1) Because non-polar molecules only have london forces
2) Polar substances have London forces and permanent dipole-dipole interactions between molecules
3) More energy is needed to break dipole-dipole interactions

Question 14

What shape is a carbonate ion?

Answer 14

Trigonal planar

CO3 -

Question 15

What shape is a nitrate ion?

Answer 15

Trigonal planar

NO3 -

Question 16

What shape is a sulfate ion?

Answer 16

Tetrahedral

SO4 2-

Question 17

What shape is an ammonium ion ?

Answer 17

Tetrahedral

NH4 +

Question 18

How are things charged in a polar molecule?

Answer 18

The more electronegative atom is negatively charged (d-) and the other atoms are positively charged (d+)

Question 19

How do you know if a molecule with more than two different atoms is polar?

Answer 19

It depends on the shape of the molecule, the dipoles may reinforce each other making a larger dipole or they may cancel each other out.

Question 20

Give an example of where two dipoles cancel each other out to make a non polar molecule?

Answer 20

Carbon dioxide

1) The two C=O have a permanent dipole
2) The molecule is symmetrical
3) The dipoles cancels out and the overall dipole is 0

Question 21

Explain how water breaks down a sodium chloride lattice (an ionic substance)?

Answer 21

1) Water attracts Na+ and Cl- ions
2) Na+ ions attracted towards oxygen of water molecules and Cl- ions are attracted towards the hydrogen in the water molecules
3) The ionic lattice breaks down and dissolves

Question 22

Why is solid Ice less dense than water?

Answer 22

Hydrogen bonds hold water molecules apart further apart in Ice than in water and this open lattice makes solid Ice less dense than liquid water and floats

Question 23

Why does water have a relatively high boiling point?

Answer 23

1) Water has london forces but also hydrogen bonds
2) A reasonably large amount of energy is needed to break the hydrogen bonds in water
3) This gives water a higher boiling point than what would be expected from just London forces.

Question 24

how permanent are induced dipoles

Answer 24

they are temporary, can appear and then disappear in an instant of time

Question 25

How do elements/ions/compounds get their shapes?

Answer 25

Shape is determined by electron pair repulsion
The electron pairs repel one another so they are as far apart as possible
Lone pairs of electrons repel more than bonded pairs of electrons

Question 26

What is a hydrogen bond

Answer 26

Intermolecular bonding between molecules containing N, O or F and the H atom of –NH, –OH or HF

Question 27

Solubility of non-polar covalent substances in polar solvents

Answer 27

1) Little interaction between molecules in lattice and solvent molecules
2) Bonds in lattice too strong to be broken
3) Tend to be insoluble

Question 28

Solubility of non-polar simple molecular substances

Answer 28

When added to a non-polar solvent

1) Intermolecular forces form between molecules and solvent
2) Interactions weaken the intermolecular forces in the simple molecular lattice
3) intermolecular forces break and compound dissolves