C2- Structure and Properties

Question 1

When can ionic substances conduct electricity?

Answer 1

When molten or dissolved in water.

Question 2

Why can ionic substances conduct electricity when molten or when dissolved in water?

Answer 2

The ions can move freely.

This allows them to carry electrical charge➡️the liquids conduct electricity.

Question 3

What are the properties of simple molecules?

Answer 3

• Low boiling points.
• Low melting points.
• Do not conduct electricity.

Question 4

Why do simple molecules have low boiling and melting points?

Answer 4

The intermolecular forces between simple molecules are weak, so little energy is needed to overcome them.

Question 5

Why don’t simple molecules conduct electricity?

Answer 5

Simple molecules have no overall charge, so they cannot carry electrical charge and do not conduct electricity.

Question 6

Why do substances with giant covalent structures have very high melting points?

Answer 6

Every atoms in a giant covalent structure is joined to several other atoms by strong covalent bonds➡️Takes a lot of energy to break the lattice➡️High melting point.

Question 7

What are diamond and graphite made of?

Answer 7

Carbon.

Question 8

What is the structural difference between diamond and graphite?

Answer 8

Each carbon atom in diamond is covalently bonded to four others, whilst every carbon atom in graphite is covalently bonded to three others.

Question 9

What differences in properties are there between diamond and graphite and why?

Answer 9

Diamond= Hard and transparent➡️Strong bonds Graphite= Slippery and Grey➡️No covalent bonds between each layer so they slide over each other

Question 10

What are fullerenes?

Answer 10

Fullerenes are large molecules formed from hexagonal rings of carbon atoms.

Question 11

Why can graphite conduct electricity and not diamond?

Answer 11

Graphite can conduct electricity (and heat) because of the delocalised electrons in its structure.

Diamond doesn’t have any delocalised electrons, so is a poor conductor.

Question 12

Why can metals be made into wires?

Answer 12

Metal atoms are arranged into layers which can slide over each other, so we can bend or stretch it into a new shape without it breaking.

Question 13

What are alloys?

Answer 13

Alloys are mixture of metals mixed with other elements.

Question 14

Why can alloys be more useful than pure metals and why?

Answer 14

Alloys are harder than pure metals because the different sized atoms distort the layers, making it more difficult for them to slide over each other.

Question 15

What do shape memory alloys do?

Answer 15

Shape memory alloys can be bent or deformed into a different shape, but can be returned to their original shape when heated.

Question 16

Why are metals good conductors of electricity?

Answer 16

Metal structure have delocalised electrons, which move through the giant metal lattice and can transfer energy quickly which makes them good conductors of heat and electricity.

Question 17

Why do low density poly(ethene) and high density poly(ethene) have different properties?

Answer 17

They are made using different catalysts and different reaction conditions.

As a result, HD poly(ethene) has a higher softening temperature and is stronger than LD poly(ethene).

Question 18

Describe the structure of thermosetting polymers and their properties.

Answer 18

Thermosetting polymers set hard when they are first moulded because strong covalent bonds form cross-links between their polymer chains. Thermosetting polymers do not soften or melt when heated.

Question 19

Give an example of a thermosoftening polymer, and describe its structure and bonding and explain why thermosoftening polymers melt when heated.

Answer 19

Poly(ethene).

Made up of individual polymer chains that are tangled together (like spaghetti). Weak intermolecular forces, so bonds are easily overcome with little energy. Thermosoftening polymers soften or melt easily when heated.

Question 20

What allows thermosoftening polymers to be remoulded?

Answer 20

In thermosoftening polymers the forces between the chains are weak.

When we heat the polymer, the weak intermolecular forces are broken and the polymer becomes soft. When the polymer cools down, the intermolecular forces bring the polymer back together so the polymer hardens again.

Question 21

Define nanoscience.

Answer 21

Nanoscience is the study of small particles between 1 and 100 nanometers in size.

Question 22

What is special about nanoparticles?

Answer 22

1 million nanoparticles= 1mm.

Their very small sizes give them a very large surface area, so nanoparticles behave differently from the bulk materials they are made from, resulting in new properties.

Question 23

Give some examples of nanoscience.

Answer 23

• Straighteners.
• Toothpaste.
• Mobiles.
• Make Up and Moisturiser.

Question 24

What are some of the properties of nano-silver?

Answer 24

Nano-silver has antibacterial, antiviral and anti fungal properties.

These tiny pieces of silver are incorporated into materials to make clothes and medical dressings which stay fresh for longer.

Question 25

What are the advantages and disadvantages to nanoscience?

Answer 25

A-Unusual properties leading to new uses.

A- Could be used to make very efficient catalysts.

A-Some have antibacterial, anti fungal and antiviral properties.

D-Increased use increases risk of them getting in the air and into our bodies➡️Unpredictable consequences on health and environment.

Question 26

Why do ionic solids have high melting points?

Answer 26

Ionic compounds are all solid at room temperature, and a lot of energy is needed to overcome the ionic bonds to melt the solids because of the strong electrostatic forces holding the ions together.

Question 27

Explain why, in terms of structure, carbon dioxide is a gas, even at low temperature.

(3 marks)

Answer 27

Has simple molecules (1). Weak intermolecular forces (1) so little energy is needed to overcome (1).

Question 28

Name the ion which makes sulfuric acid solution acidic.

Answer 28

Hydrogen.

Question 29

Nitinol is an alloy used in dental braces- suggest why this is.

Answer 29

Nitinol is a smart alloy, so can remember it’s original shape.

Question 30

Carbon atoms are bonded in a nanotube like a single layer of graphite.

Suggest why carbon nanotubes are used as lubricants (2 marks).

Answer 30

Nanotubes slide over each other (1) because there are no covalent bonds between the nanotubes (1).