C2.2 How structure influences the properties and uses of substances

Question 1

Do simple molecules conduct electricity?

Answer 1

No

Question 2

Why do simple molecules not conduct electricity?

Answer 2

because the molecules do not have an overall change

Question 3

Why do ionic compounds have high melting and boiling points?

Answer 3

as there are strong electrostatic forces in all directions between oppositely charged ions. Large amounts of energy are needed to break many strong bonds

Question 4

When can ionic compounds conduct electricity, why?

Answer 4

when melted or dissolved in water.

can conduct electricity because ions can move and carry a current

Question 5

give an example of an ionic compound

Answer 5

sodium chloride

Question 6

Why do giant covalent structures- macromolecules, have high boiling and melting points?

Answer 6

As all atoms are linked to other atoms by strong covalent bonds.

Question 7

How many covalent bonds does carbon form in diamond?

Answer 7

4

Question 8

How many covalent bonds does carbon form in graphite?

Answer 8

3

Question 9

Why are there layers in graphite?

Answer 9

As each carbon atom bonds to 3 other carbon atoms

Question 10

Why is graphite soft and slippery?

Answer 10

each carbon bonds with 3 other carbon atoms which forms layers. Layers are free to slide over each other as there are no covalent bonds between the layers so therefore weak intermolecular forces between layers.

Question 11

Why can graphite conduct electricity?

Answer 11

One electron from each carbon atom in graphite is delocalised. These delocalised electrons allow graphite to conduct heat and electricity

Question 12

Describe the structure of fullerenes

Answer 12

hexagonal rings of carbon atoms

Question 13

What can fullerenes be used for?

Answer 13

drug delivery into the body. in lubricants, as catalysts, and in nanotubes for reinforcing materials eg in tennis rackets

Question 14

What does conduction depend on?

Answer 14

the ability of electrons to move throughout the metal

Question 15

Why do metals conduct heat and electricity?

Answer 15

because of the delocalised electrons in their structures

Question 16

Why can metals be bent and shaped?

Answer 16

atoms arranged in regular layers. These layers are able to slide over each other.

Question 17

Why are alloys harder than pure metals?

Answer 17

Alloys are made from 2 or more different metals. The different sized atoms of the metals distort the layers in the structure, making it more difficult for them to slide over each other.

Question 18

Give an example of a shape memory alloy

Answer 18

Nitinol used in dental braces

Question 19

What do shape memory alloys do?

Answer 19

return to their original shape after being deformed

Question 20

What do the properties of polymers depend on?

Answer 20

what they are made from and the conditions under which they are made

Question 21

What conditions are needed to make low density polythene?

Answer 21

high temperature and pressure

Question 22

What conditions are needed to make high density polythene?

Answer 22

Lower temperature and pressure

catalyst

Question 23

Describe the structure and properties of thermosoftening polymers

Answer 23

individual, tangles polymer chains. Weak intermolecular forces between chains so easy to separate, melt and recycle

Question 24

Describe the structure and properties of thermosetting polymers

Answer 24

polymer chains with cross links (covalent bonds) between them so strong intermolecular forces between bonds. Means that they do not melt when heated- high melting point so can not be recycled

Question 25

What structures does nanoscience refer to?

Answer 25

structure that are 1-100 nanometers in size and contain a few hundred atoms.

Question 26

4 key points about nanoparticles

Answer 26

• 1-100 nanometers in size
• contain a few hundred atoms
• nanoparticles show different properties to the same materials in bulk
• have a high surface area to volume ratio

Question 27

What can nanoparticles be used to make?

Answer 27

new computers, catalysts, stronger and lighter construction materials, new cosmetics

Question 28

Why do substances that consist of simple molecules have relatively low melting and boiling points?

Answer 28

There are weak intermolecular forces between the molecules. It is these intermolecular forces that are easily overcome, not the strong covalent bonds when a substance melts or boils.

Question 29

Why is silica used to make brinks for high temperature furnaces?

Answer 29

It has a high melting point (it is a macromolecule)

because each silicon atom is covalently bonded to 4 oxygen atoms

These covalent bonds are very strong so a lot of energy is needed to break them

it is unreactive , hard and a poor conductor of heat as there are no free electrons

Question 30

Explain why nanoparticles pass through the skin and travel around the body more easily than normal-sized particles

Answer 30

as they are smaller- only a few atoms in size

so they can easily pass through the skin

Question 31

Explain why thermosoftening polymers would not be suitable for packaging very hot food

Answer 31

They have a low melting point so would melt

This is because there are no crosslinks between chains

so there are weak intermolecular forces

Question 32

Why is silicon dioxide a suitable material for lining furnaces?

Answer 32

It has a high melting point (as it is a macromolecule)

because a lot of energy is needed to break bonds

This is because the bonds are covalent and so are very strong

Question 33

Explain why copper is a good conductor of electricity

Answer 33

Copper has delocalised electrons which can move through the structure and carry a charge

Question 34

Explain why carbon dioxide has a very low boiling point

Answer 34

Carbon dioxide is simple molecular

There are weak intermolecular forces between the molecules

so only a small amount of energy is needed to separate the molecules

Question 35

Explain why graphite is softer than diamond

Answer 35

because there are layers in graphite that can slide

this is because there are only weak intermolecular forces between layers

however in diamond, each carbon atom is covalently bonded to 4 others

so no carbon atoms are able to move

Question 36

Explain hy graphite conducts electricity but diamond does not

Answer 36

because graphite has delocalised electrons which can carry a current and move throughout the structure

however, diamond has not delocalised electrons

Question 37

Suggest why carbon nanotubes are used as lubricants

Answer 37

nanotubes can slide over each other

because no covalent bonds between the nanotubes