S2.4 - from models to materials

Question 1

What is chemical bonding?

Answer 1

Chemical bonding is best described as a continuum between the ionic, covalent and metallic models, not a discrete model.
- Shown by the bonding triangle.

Question 2

What does position of triangle depend on?

Answer 2

Electronegativity values

Question 3

What is the bonding triangle?

Answer 3

Used to illustrate the types of chemical bonding as a continuum.

Question 4

What goes on the x-axis of the bonding triangle?

Answer 4

Average electronegativity

Question 5

What goes on the y-axis in the bonding triangle?

Answer 5

Difference in electronegativity

Question 6

Where do elements fit in the bonding triangle?

Answer 6

Along the x-axis

Question 7

What are the properties and bonding of Na, Mg and Al2O3?

Answer 7

Properties:
- High melting and boiling points
- Electrical conductors when molten
Bonding:
- Ionic metallic oxides

Question 8

What are the properties and bonding of SiO2?

Answer 8

Properties:
- High melting and boiling points
- Electrical conductors
Bonding:
- Giant covalent oxides of the metalloid silicon

Question 9

What are the properties and bonding of P, SO2?

Answer 9

Properties:
- Low melting and boiling points
- Non-conductors of electricity
Bonding:
- Covalent non-metallic oxides

Question 10

What does the composition of a compound determined by?

Answer 10

Position of a compound in the bonding triangle is determined by the relative contributions of the three bonding types to the overall bond.

Question 11

What is AlCl3 classed as?

Answer 11

It should come out as more covalent, suggesting a lower melting point.

Question 12

What is a composite material?

Answer 12

Heterogeneous mixture made up of at least 2 materials, which are present at separate phases.

Question 13

What happens to the properties of substances in a composite material?

Answer 13

Each element keeps its own properties, leading to a final product with enhanced properties designed for a particular purpose.

Question 14

What are examples of composite materials?

Answer 14

Reinforcement bar - concrete and steel bars
Adobe bricks - mud and hay

Question 15

What is an alloy?

Answer 15

Homogeneous mixtures containing at least 1 metal held together by metallic bonding.

Question 16

What are some examples of alloys?

Answer 16

Steel - iron + carbon
Bronze - copper + tin
Brass - copper + zinc

Question 17

Why are alloys hard?

Answer 17

Alloys are hard as the layers are different sizes and distorted, meaning that they do not slide or change shape when a force or pressure is applied.

Question 18

How can factors affect the strength of a metallic bond?

Answer 18

Number of delocalised electrons - more electrons means a stronger electrostatic attraction, which requires more energy to overcome.
Charge of cations - higher charge means more delocalised electrons moving through the lattice with smaller radii as ENC increases, causing a stronger attraction.
Radius of cation - smaller radius means a stronger attraction between the electron and nucleus.

Question 19

What are trends of metals down the group and across the period?

Answer 19

Down the group - larger radii means weaker electrostatic attraction, so a lower melting point as less energy is needed to overcome this.
Across the period - larger ENC and smaller ionic radius means larger charge density and stronger attraction, so a higher melting points as more energy is needed to overcome this.

Question 20

What is a polymer?

Answer 20

Large molecules (macro-molecule) made up of repeating sub-units (monomers).

Question 21

What are properties of polymers?

Answer 21

• Covalent bonding
• Unique ability to form stable bonds with itself, H and other elements.

Question 22

How do the side chains affect the polymer?

Answer 22

Different side chains change the type of IMF formed, which affects the polymer made and the properties it has.

Question 23

What is a repeating unit?

Answer 23

A ‘snapshot’ at a part of chain which has the part that repeats.

Question 24

What are the two types of polymers and what are some examples?

Answer 24

Natural polymers - protein, starch and DNA
Synthetic polymers - plastic

Question 25

What are the properties of plastic?

Answer 25

• Light-weight
• Low reactivity
• Water-resistant
• Strong
• Non-biodegradable
• Made out of cellulose, starch and lignin

Question 26

What does compostable mean?

Answer 26

Can be broken down along with food and plant matter in specific conditions.

Question 27

What does biodegradable mean?

Answer 27

Can be broken down by microorganisms

Question 28

What does non-biodegradable mean?

Answer 28

Cannot be broken down by natural processes.

Question 29

What does reusable mean?

Answer 29

Can be used in the same format over and over again.

Question 30

What does recyclable mean?

Answer 30

Can be melted down and changed into something else.

Question 31

What is an addition polymer?

Answer 31

Requires a double bond to be broken to make a new covalent bond with neighboring molecules to form a chain.

Question 32

How does polymerization link to atom economy?

Answer 32

Has 100% atom economy - no waste products

Question 33

What are the disadvantages of addition polymers?

Answer 33

• Requires huge amounts of energy which is expensive and bad for the environment.