Chapter 6 (approved)

Question 1

What do electron pairs do to each other?

Answer 1

They repel each other

Question 2

What determines the shape of the ion or molecule?

Answer 2

Number of bonding and lone pairs surrounding the central atom

Question 2

Why do lone pairs repel more strongly than bonding pairs?

Answer 2

Because lone pairs are closer to the central atom and occupy more space than bonded pairs

Question 3

Describe a molecule of methane, CH4 (3)

Answer 3

Symmetrical, four bonded pairs and 0 lone pairs surround the central atom, the bonding pairs repel equally

Results in a tetrahedral shape with 4 equal bond angels of 109.5 degrees

Question 4

What is a bonding region?

Answer 4

A region between two atoms which can contain single or multiple bonds

Question 5

Linear: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 5

Two solid lines, 2 bonding, 0 lone, 180 degrees

Question 6

2 Non-linear/bent: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 6

Two solid lines and a pear, 2 bonding, 0 lone, 117.5 degrees

Question 7

Trigonal planar: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 7

3 solid lines, 3 bonding, 0 lone, 120 degrees

Question 8

Tetrahedral: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 8

1 dotted wedge, 1 solid wedge, 2 solid lines; 4 bonding, 0 lone, 109.5 degrees

Question 9

Trigonal pyramidal: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 9

1 pear, 1 dotted wedge, 1 plain wedge, 1 solid line; 3 bonding, 1 lone, 107 degrees

Question 10

4 Bent: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 10

2 pears (to represent lone pairs) , dotted wedge, solid wedge, 2 bonding, 2 lone, 104.5 degrees

Question 11

Octrahedral: structure (wedges), number of bonding pairs, lone pairs, bond angle

Answer 11

2 solid lines (top, bottom), 2 dotted wedges (top left, right corner), 2 solid wedges (bottom left, right corner); 6 bonding pairs, 0 lone pairs; 90 degrees

Question 12

Covalent bond def.

Answer 12

The electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 13

Electronegativity def.

Answer 13

The ability of an atom to attract the bonding pair in a covalent bond

Question 14

Factors that affect electronegativity

Answer 14

Nuclear charge
Atomic radius
Electron shielding

Question 15

What is nuclear charge, how does it affect electronegativity and why?

Answer 15

The positive charge in the nucleus, which is determined by proton number
Increase in the number of protons increases electronegativity
As there is an increase in nuclear attraction for the outer shell electrons

Question 16

What is atomic radius, how does it affect electronegativity and why?

Answer 16

Atomic radius is the distance between the nucleus and the outermost electrons
Increase in atomic radius decreases electronegativity
As the nucleus and outer shell electrons are further away, so the electrostatic attraction between them is weaker

Question 17

What is electron shielding, how does it affect electronegativity and why?

Answer 17

Electron shielding is when filled energy levels shield the effect of nuclear charge
Increased electron shielding (caused by more electron shells) leads to lower electronegativity
It weakens the electrostatic attraction between the nucleus and the outer electrons

Question 18

How does electronegativity change down a group?

Answer 18

It decreases

Question 19

How does electronegativity change across a period?

Answer 19

It increases

Question 20

How does nuclear charge change across a period?

Answer 20

It increases

Question 21

How can you use electronegativity difference to estimate the type of bonding in the molecule?

Answer 21

Similar electronegaitvity suggest a covalent bond, large difference suggests an ionic bond

Question 22

Non-polar bond

Answer 22

Where the bonded electron pair is shared equally between the bonded atoms
which occurs when..
The bonded atoms are the same or have similar electronegativity

Question 23

Polar bond

Answer 23

The bonded electron pair is shared unequally between the bonded atoms

Question 24

Intermolecular forces

Answer 24

The weak interactions between the dipoles of different molecules

Question 25

Three types of im forces

Answer 25

London forces
Permanent dipole-dipole forces
Hydrogen bonding

Question 26

How London forces are formed

Answer 26

Movement of electrons produces a changing dipole in a molecule
At any instant, an instantaneous dipole will exist, but its posiiton is constantly shifting
The induced dipole induces further dipoles on neigbouring molecules, which then attract one another

Question 27

How does the number of electrons change the strength of London forces?

Answer 27

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 28

Describe a Simple molecular lattice

Answer 28

Molecules are held togther by weak intermolecular forces
Atoms are bonded by strong covalent bonds

Question 29

Why do simple molecular substances have low melting and boiling points?

Answer 29

When a simple molecular lattice is broken, only the weak intermolecular forces are broken, which reuqire little energy to overcome, the strong covalent bonds are not broken

Question 30

Can simple molecular substances conduct electricity

Answer 30

They are non-conductors as they have no mobile charge carriers

Question 31

When are simple molecular substances soluble ?

Answer 31

Like dissolves like
Simple molecular substances are non-polar
So they are soluble in non-polar solvents
And insoluble in polar solvents

Question 32

Hydrogen bonding

Answer 32

A type of permanent dipole-dipole interaction found between molecules with an electronegative atom with a lone pair and a hydrogen atom attached to an O, N or F atom

Question 33

How is a hydrogen bond represented and where does it act?

Answer 33

It is represented by a dashed line, and acts between a lone pair and a hydrogen atom of a different molecule

Question 34

Why is ice less dense than water?

Answer 34

Hydrogen bonds hold water molecules apart in an open lattice structure when in ice
When it melts, the ice lattice collapses and the molecules move closer together, decreasing the density

Question 35

Anomolous properties of water due to hydrogen bonding

Answer 35

Ice being less dense than water
Water’s high melting and boiling point
Water’s high surface tension
Water’s high viscosity

Question 36

Why does water have such a high melting and boiling point?

Answer 36

Hydrogen bonds are additional forces above London forces, they are very strong so a lot of energy is required to overcome them leading to a high melting and boiling point