Shapes of molecules and intermolecular forces

Question 1

Explain the electron pair repulsion theory

Answer 1

Electrons surrounding an atom determine the shape of the atom
Electron pairs repel one another so that they are arranges as far apart as possible
Arrangement of electrons minimises repulsion and creates a definite shape

Question 2

What does a solid line represent?

Answer 2

Represents a bond on the plane of the paper

Question 3

What does a solid wedge represent?

Answer 3

Represents a bond coming out the plane of the paper

Question 4

What does a dotted wedge represent?

Answer 4

Represents a bond going into the plane of the paper

Question 5

Where are lone pairs located in relation to central atom?

Answer 5

Closer to the central atom as occupies more space

Question 6

What electrons repel more strongly?

Answer 6

Lone pairs

Question 7

Explain a tetrahedral shape

Answer 7

4 bonded pairs
No lone pairs
Bond angle 109.5

Question 8

Explain a pyramidal shape

Answer 8

3 bonded pairs
One lone pair
Bond angle 107

Question 9

Explain a non-linear shape

Answer 9

2 bonded pairs
2 lone pairs
Bond angle 104.5

Question 10

Explain a linear shape

Answer 10

2 bonded regions
No lone pairs
Bond angle 180

Question 11

Explain a trigonal planar shape

Answer 11

3 bonded regions
No lone pairs
Bond angle 120

Question 12

Explain an octahedral shape

Answer 12

6 bonded regions
No lone pairs
Bond angle 90

Question 13

What shape are carbonate and nitrate ions?

Answer 13

Trigonal planar

Question 14

What shape are sulphate ions?

Answer 14

Tetrahedral

Question 15

Define ‘electronegativity’

Answer 15

A measure of attraction of a bonded atom for the pair of electrons in a covalent bond

Question 16

What are the most electronegative elements?

Answer 16

Fluorine
Oxygen
Nitrogen
Chlorine

Question 17

What scale is electronegativity measured on?

Answer 17

Pauling electronegativity scale

Question 18

How does electronegativity affect whether the bond is ionic or covalent?

Answer 18

The greater the difference electronegativity value is the more likely it is to be ionic because one bonded atom will have a much greater attraction for shared pair of electrons

Question 19

What does it mean for a bond to be non-polar?

Answer 19

The bonded electron pair is shared equally between the bonded atoms

Question 20

When do non-polar bonds occur?

Answer 20

The bonded atoms are the same

The bonded atoms are the same or have a similar electronegativity value

Question 21

What is a pure covalent bond?

Answer 21

The bonded atoms come from the same element and the bond is shared equally

Question 22

What is a polar bond?

Answer 22

The bonded electron air is shared unequally between the atoms

Question 23

What is polar covalent bond?

Answer 23

Bonded atoms are different and there is a difference in electronegativity values

Question 24

Define ‘dipole’

Answer 24

Separation of opposite charge

Question 25

When does a permanent dipole occur?

Answer 25

A dipole in a polar covalent bond that doesn’t change

Question 26

Define ‘intermolecular forces’

Answer 26

The weak interactions between dipoles of different molecules

Question 27

What are the 3 types of intermolecular force?

Answer 27

London Forces
Permanent dipole-dipole
Hydrogen bonding

Question 28

What properties do different types of bond affect?

Answer 28

Intermolecular Forces= physical properties

Covalent bonds= chemical properties

Question 29

Describe process of London forces forming

Answer 29

Movement of electrons produce a changing dipole
An instantaneous dipole will form but location is constantly changing
Instantaneous dipole induces a dipole in neighbouring molecule
Induced dipole induces further dipoles in neighbouring molecules

Question 30

How does change in number of electrons affect strength of London forces?

Answer 30

The more electrons:
the larger the instantaneous and induced dipoles
the greater the induced dipole-dipole interactions
the stronger the attractive forces between molecules

Question 31

Where do permanent dipole dipoles form?

Answer 31

Between permanent dipoles in different polar molecules

Question 32

What is a simple molecular lattice made up of?

Answer 32

Simple molecules( small units containing a definite number of atoms with a definite formulae)

Question 33

How are molecules held together in a simple molecular lattice?

Answer 33

The molecules are held in place by weak intermolecular forces
The atoms within the molecules are held in place by strong covalent bonds

Question 34

What are the boiling points of simple molecular substances like?

Answer 34

Low, the weak London forces between molecules can be broken at very low levels of energy. Covalent bonds are NOT broken.

Question 35

Describe the solubility of non polar simple molecular substances in non-polar solvents

Answer 35

Intermolecular forces form between the molecules and the solvent
Interactions weaken the IF in the simple molecular lattice
IF forces break and compound dissolves

Question 36

Describe solubility of simple molecular substances in polar substances

Answer 36

Little interaction between molecules in lattice and solutes as IF forces between the polar solvent is too strong.

Question 37

Describe electrical conductivity of simple molecular substances

Answer 37

Not conductive as no mobile charged particles

Question 38

Where do hydrogen bonds form?

Answer 38

A hydrogen atom attached to an electronegative atom

Question 39

Why is solid water less dense than liquid water?

Answer 39

Hydrogen bonds hold water molecules apart in an open lattice structure when solid
The water molecules in ice are further apart than in water
Solid ice is less dense so floats

Question 40

Why does water have an anomalously high melting and boiling point?

Answer 40

Due to the presence of hydrogen bonds