Metals

Question 1

Answer 1

Body Centred Cubic (BCC)

More open structure

Coordination number- 8

Packing Density- 68%

Slip systems- 48 (planes are not close packed needing high temp. or force to activate)

Question 2

Answer 2

Hexagonal Close Packing (HCP)

Each atom is surrounded by 6 more

Coordination number- 12

Packing Density- 74%

Slip systems- 3 (brittle)

Question 3

How do you reduce slip in metals and why?

Answer 3

1. Alloying
2. Decrease grain size

Makes a metal harder/stronger or more brittle

Question 4

Elastic Deformation

Answer 4

Stress is proportional to strain, is reversible

Question 5

Malleability

Answer 5

The ability of a solid material to deform under compression

Question 6

Types of Alloys

Answer 6

1. Interstitial- Alloying atoms fit between metal atoms (Carbon in Steel)
2. Substitutional- Alloying atoms replace other metal atoms (Brass with Copper and Zinc)

Question 7

How does Grain Size affect the mechanical properties of metals?

Answer 7

Less slip across grain boundaries

Smaller grain means more boundaries which means harder to slip which means harder/stronger metal

Small grains are obtained by fast cooling, use of chemical agents, or application of physical treatment

Question 8

Coordination Number?

Answer 8

Amount of neighbour atoms

Question 9

Suitability of a metal

Answer 9

CASE

Cheap

Abundant

Suitable for the task

Easy to extract

Question 10

Brittle

Answer 10

Materials considered this if they fracture at less than 5% strain

Question 11

Ductility

Answer 11

A measure of the extent of plastic deformation a material can sustain before fracturing. Can be drawn into wires

Question 12

Metallic Glass

Answer 12

Disordered structure like a liquid

High strength and elastic limit

Resistant against corrosion/scratches/dents/wear

Brittle

Question 13

Answer 13

Cubic Close Packing (CCP)

Each atom is surrounded by 6 others in each layer

Coordination number- 12

Packing Density- 74%

Slip systems- 12 (4 slip planes, 3 directions) (ductile)

Question 14

How do Metallic Grains form?

Answer 14

1. As a metal solidifies, crystals start to grow in all different directions
2. These merge to give a grain structure where each grain has its own crystalline orientation

Question 15

Where are small grains not wanted?

Answer 15

High temp. strength

Temp-induced slip/failure more likely along the grain boundaries

Jet Turbines

Question 16

Plastic Deformation

Answer 16

Deformation in which stress and strain are no longer proportional, not reversible

Question 17

Anode and Cathode (metal corrosion)

Answer 17

The anode defines the area at which oxidation takes place

The cathode defines the area at which reduction takes place (where oxide layer forms)

This is always true!

Question 18

Example of REDOX reactions

Answer 18

• Corosion
• Extraction of metals
• Batteries/Fuel Cells
• Burning of fuels

Question 19

Transistion Metals

Answer 19

d-block elements lose the valence s-electrons when they form compounds but most can also lose a variable number of d-electrons. Explains mulitiple oxidation states

Question 20

Trends across a Period

Answer 20

Atomic Radius- Increases

Ionisation energy- Decreases

Oxidising Strength- Decreases

Reducing Strength- Increases

Question 21

Ionisation energy

Answer 21

The energy required to remove one electron from an atom of the element in the gas phase

Question 22

Metals in Nature

Answer 22

Generally form positive ions which combine non metal negative ions, forming ores

Question 23

Electrochemical Potential

Answer 23

It is a measure of the chemical potential of compounds which takes electrostatic forces into account