chapter 4 - metallic bonding

Question 1

properties of metals

Answer 1

• lustrous
• conductors of heat
• conductors of electricity
• malleable
• ductile = drawn into wires
• high density
• majority have high melting points

Question 2

what is the process of alloying

Answer 2

when a metal is mixed with another metal to change its properties, the new metal is called the alloy

Question 3

substitutional alloy

Answer 3

occurs when metals of a similar size are used to form an alloy, therefore they can replace each other in the metal crystals eg. sterling silver = silver+copper

Question 4

interstitial alloy

Answer 4

when the sizes of the metals in the alloy greatly differ, the smaller atoms fit into the spaces between the larger atoms eg. steel = iron + carbon

Question 5

what happens when a metal bends

Answer 5

layers of atoms slide over each other, the easier they slide the easier the bend

• a metal with perfect rows = bends easy
• a metal with distorted rows = atoms cannot slide

Question 6

how do metals crystallise

Answer 6

they form areas of perfect close-packing called grains, between the grains are grain boundaries

Question 7

large grains means

Answer 7

have fewer dislocations and bend easily

Question 8

small grains means

Answer 8

many dislocations and do not bend easily

Question 9

work hardening a metal

Answer 9

• by hammering/bending cold metals causes the crystal grains to become smaller, therefore making it hard to bend and tough
• work hardened metals become more brittle due to more dislocations
• if constantly bent it will cause the metal to snap

Question 10

annealed metals

Answer 10

• are heated to red hot then slowly cooled

- used to restore ductility lost when work hardened

Question 11

quenched metals

Answer 11

• heated until red hot and then cooled quickly in cold water
• this technique creates smaller crystals making them more brittle

Question 12

tempered metals

Answer 12

• when quenched metals are warmed again to a lower temp and then cooled slowly
• reduces brittleness of the metal however, keeping the hardness

Question 13

ways to protect metals

Answer 13

• plastic by covering the surface area
• paint can be used for larger objects
• grease and oil can be used to coat moving parts of machinery

Question 14

how is iron extracted from its ores?

Answer 14

by using the process of the blast furnace which separates the iron ready for use