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Flashcards in Metals Deck (49)
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1

Physical properties of metals

Lustrous: How well the substance reflects light. Most metals can be polished to a high lustre ie shiny, reflective.
Malleability: can be beaten/pressed into various shapes without breaking.
Electrical conductivity: are good conductors because electrons are delocalised therefore free to move and carry charge
Ductility: can be drawn into wires
State at room temperature: solid except mercury because of high melting and boiling points.
Melting point: Pure metals have a precise melting point. Varies from 100°C - above 1000°C
Boiling point: Pure metals have a precise boiling point. Most metals have boiling points above 1000°C.
Thermal conductivity: how easily heat energy can be passed through a substance. Metals are good conductors of heat as atoms are tightly packed together.
Sonorous: ring when struck
Density: gmL-1 Most metals have high densities (above 3gmL-1) except Na and Li which can float on water (ie less than 1gmL-1)
Colour: related to a substance's ability to reflect light. Most metals are silver-grey. Copper is pink and gold is yellow.
Hardness: many pure metals such as Mg, Al or Fe, are too soft to be used for engineering purposes and are hardened by making an alloy of the metal. Lithium and Na are soft enough to be cut by a knife

2

Lustre of metals

All metals have a high lustre. However, some metals have a dull appearance due to their reaction with oxygen or water in the atmosphere.

3

Colours of metals

Silver grey: Ca, Fe, Pb, Li
Silver: Al, Mg, Ag, Na, Zn
Pink: Cu
Gold: Ag

4

Density of metals

Metals have high densities because the atoms are tightly packed together. When a layer of atoms is placed on top of another layer, the atoms move into the gaps between the atoms of the previous layer.
A metal's density depends on their atomic masses and how tightly packed the atoms are.

An atom in the middle of arrangement touches 6 other atoms.

5

Electrical conductivity of metals

Metals are good conductors of electricity because the valence electrons are delocalised and therefore free to move within the metal structure. So when electrons flow out of the negative terminal of a power supply and into a metal, the electrons within the metal are able to carry the current to the positive terminal of the power supply.

6

Why do metals have high boiling and melting points

Because there are strong forces of attraction between the atoms due to the delocalised valence electrons. Because the e- are free moving, a metal actually consists of positive ions (the nuclei) surrounded by a sea of e-. The sea of e- are attracted to the neighbouring positive ions, meaning that these attractive forces require a lot of energy to break.

Delocalised - can be attracted to other positive nuclei.

7

Malleability and Ductility

The attractive forces between atoms is strong, however, they are not rigid (fixed in place). Layers of atoms can slide over each other when a force is applied. When the force is removed the atom's closely packed arrangement is restored. The atoms slide and settle into a new position once the force is removed.

Metallic bonds are non-directional.

8

Thermal conductivity

Particles inside a metal vibrate in a fixed position. The particles closest to the heat source gain Ek and vibrate more vigorously. These more energetic particles collide with the unheated particles, passing some of the Ek on and also causing those particles to start vibrating more vigorously. The process of particles colliding continues. Heat energy is transferred from the hot end of the rod, to the cold end, until the entire thing is hot.

9

What is an alloy

A mixture of two or more elements in a solid solution in which the major component is a metal

10

How are alloys made

By mixing two or more molten metals (components) and allowing the mixture to cool. This makes a mixture, NOT compound, meaning that they have variable composition and properties depending on how much of each metal/non-metal is added.

11

Eg of alloys

Bronze: Copper and tin. Protects itself with an attractive coating that lasts for centuries.
Brass: Copper and zinc. Does not corrode as easily as Cu and retains an attractive lustre. Retains good electrical conductivity of Cu.
Steel: Iron and carbon.
Solder: Tin and lead - melts at a lower temperature than either Sn or Pb and can bond with many metals.
Duralumin: Aluminium, Cu and Mg - has greater strength than Al but retains the low density needed for aeroplane construction.

12

Where are alloys used

Where they have properties that are different to the metals they contain, so they become more useful than the separate component metals

13

Do alloys have specific melting points

No because it is a mixture of metals

14

Describe steel

Fe and C (0.5-2%)
It's harder, stronger and more flexible than iron and doesn't corrode as quickly as iron.
High tensile strength - can be bent and return to their original shape without breaking.

15

Why are alloys harder than pure metals

Because adding different sized atoms breaks up the regular arrangement (crystalline structure lattice) of atoms in a metal. This means when a force is applied to an alloy the atoms cannot slide pass each other as easily as they can in a pure sample of the metal.

The atoms of the different size replaces a small number of atoms of the parent metal. The layers of atoms cannot move over each other as well (up to a point), making the alloy harder than pure metal. Less force is required to make the atoms slide past each other in pure metals.

16

Atomic structure of metals

Atoms are strongly attracted to each other so they form a close-packed lattice, which results in a hard crystalline material.

17

Once the percentage of the larger atom increases, what happens

There is more space between the metal atoms, so the atoms are able to slide past each other more easily. It begins to approach the relative strength of the element. Disrupts the regular arrangement of the smaller atoms to the point that the smaller atoms cannot bond together as strongly.

18

Reaction of metals and acid

Metal + Acid -> Metal salt + hydrogen

Test for hydrogen with lit splint

19

What is the common feature of metals

Low number of valence electrons.

20

What determines how reactive a metal is

The ease with which the valence electrons are removed from the atom and a positive ion is formed.

21

Equation for metal + oxygen

Metal + Oxygen -> Metal oxide

22

Extent of metals' reaction with oxygen

-Very reactive metals: lose shiny appearance when exposed to air and become dull as a coating of oxide forms
- less reactive metals: tarnish (react with air) over a period of time
-Silver and gold retain their shiny appearance. ie do not react.

23

Colour of metal surfaces after oxidation

Group 1: white
Group 2: white
ZnO: white
Al2O3: white
CuO: black
Ag2O: brown-black
Fe2O: Black
Fe2O3: black (when hydrated red (rust))
PbO: yellow

24

Reactivity of metals with oxygen

-Li, Na react so rapidly they must be kept under oil. ie react spontaneously
-Li, Na, Ca, Mg burn rapidly in air, releasing heat and light energy.
-Al reacts rapidly to form an unreactive layer of aluminium oxide on the surface that protects it from further corrosion. Layer must be removed so it can further react with oxygen.
-Zn and Fe are more difficult to burn but will do so if the metal is finely divided or burned in oxygen. Fe will rust over several days or weeks.
-Cu and Pb react with air very slowly. Can be sped up by heating.
-Au and Ag do not react with oxygen under any conditions.

25

Reaction of metal and cold water

Metal + water -> metal hydroxide + hydrogen

26

Which metals react with cold water?

Li, Na and Ca react vigorously (at an observable rate) with cold water to produce metal hydroxide SOLUTION and hydrogen. The heat given off by this reaction can be sufficient to ignite the H2 gas formed and result in an explosion.

Mg react slowly with cold water to produce magnesium hydroxide and hydrogen gas.

Metal hydroxide turns blue in UI

27

Reaction of metal and steam

Metal + water (steam) -> metal oxide and H2

28

Which metals react with steam?

-Mg react vigorously with steam to produce MgO and H2.
-Iron and zinc react with steam ONLY when the metal is heated strongly
-Al reacts with water/steam only when the oxide layer coating is removed
-Pb, Cu, Au and Ag do not react at all with water or steam.

29

What do we observe when a metal reacts with an acid

Efflorescence and a colourless, odourless gas is produced (H2)

The metal salt produced may not be visible because it's soluble but it can be recovered by evaporation (of the water)

30

eg of metal reactions with acid

-Na and Li have violent reactions with HCl and H2SO4.
-Ca and Mg have vigorous reactions with HCl and H2SO4
-Al has delayed reaction with HCl (until acid has removed oxide layer) and no reaction with H2SO4 due to oxide layer.
-Zn has moderate reaction with HCl and H2SO4
-Fe has slow reaction with HCl and H2SO4
-Pb has no visible reaction. Reacts with HCl but insoluble lead chloride is formed, which prevents any further reaction. Reacts with H2SO4, but insoluble lead sulphate is formed, which prevents any further reaction.
-Cu, Ag and Au do not react with HCl and H2SO4


HCl and H2SO4 are aq

31

What is corrosion

When metals are exposed to the environment they can break down. Rusting is the term used to describe the corrosion of iron.

32

Three conditions for rusting to occur

1. oxygen
2. water
3. electrolyte

33

Rusting equation

4Fe + 3O2 => 2Fe2O3

34

How can corrosion be prevented

By creating a barrier between the iron and the environment. eg coating the iron in grease, plastic or paint. Or coated in more reactive metals such as zinc. Ie galvanising

Grease prevents air
Rusting needs both air and water

35

Features of corrosion reaction

Rust is red brown in colour. Flaky

36

What is reactivity to do with?

How tightly valence electrons are held to the nucleus. The easier the e- is able to be removed the more reactive the metal.

37

Explain the reactivity of alkali metals?

As you go down the group the reactivity increases. This is because there are more electron shells, meaning that the valence shell electron is further away from the nucleus and therefore the force of attraction is weaker, meaning that less energy is required to lose electron so the lower alkali metals are more reactive

38

Examples of reactions of Li, Na and K with water

Li and water:
Metal melts due to exothermic reaction and forms a liquid ball.
Floats and moves around the surface.
H produced may ignite and burn with a red flame

Na and water
Vigorous exothermic reaction
Floats and moves quickly around on the surface
Ignites, burns with a yellow flame and may explode.

K and water
Extremely vigorous reaction
Ignites instantly and burns with a purple/lilac flame
Usually explodes

39

Why is H in the reactivities series?

Resembles the ion formation of metals. Can also displace some metals form their salt solutions.

40

What happens to the metals below H?

They do not react with water or dilute acid.

41

The more reactive the metal, the less reactive the metal ion

eg Na is very reactive but Na+ isn't

42

Why is aluminium unreactive even though it is high in the reactivity series?

In reality, Al is very reactive. It reacts with oxygen very rapidly and forms aluminium oxide, Al2O3. The oxide has the ability to adhere to the surface of the underlying metal and is very difficult to remove. This thin but very hard layer of oxide then protects the underlying metal from further reactions. If the oxide becomes scratched and the metal is exposed, more oxide is formed and the protective layer is renewed. Even if Al is cleaned with sandpaper, a protective layer of Al oxide will form before the metal could be put into an acid or other solution. The Al2O3 protective layer makes the metal both DURABLE and unreactive. Therefore, AL is ideal for using to package food and drinks, despite the fact that Al is quite high on the activity series.

43

The Al2O3 layer makes the Al what?

DURABLE and UNREACTIVE

44

What is sacrificial protection?

Attaching a more reactive metal to a less reactive metal to provide protection against corrosion.

45

Explain sacrificial protection

For large iron or steel structures eg ships and underwater pipelines, painting only provides limited protection. If it gets chipped or scratched the underlying metal will be exposed and prone to corrosion. A more effective method is to attach a black of reactive metal (usually zinc) to the structure.
The reactive metal releases e-
eg 3Zn -> 3Zn2+ + 6e-

These e- then flow into the iron structure, giving it a small neg charge. This makes it harder for iron to form pos ions as this would add even more e- to the already neg charged structure. Any iron that does form pos charged ions are quickly reduced back into iron atoms.
2Fe2+ + 6e- -> 2Fe

The iron remains intact but the reactive metal block is eaten away and has to be replaced.

46

Explain galvanising

Galvanising is a process in which a metal surface is given a coating of zinc. It is used to protect iron and steel. Zinc is heated to temp greater than 420°C (melting point). The metal to be coated is chemically cleaned and then dipped into the molten zinc. The coated metal is then cooled and the zinc adheres to it. Zinc is reactive, and like Al, oxidises to form a protective zinc oxide layer on its outer surface. If the zinc coating is damaged and the underlying metal is exposed, the zinc reacts sacrificially and the underlying metal is protected.

47

Why is steel used instead of iron for transport, construction, containers, tools and instruments?

Because pure iron is difficult to obtain, and is relatively soft (grey)

48

Why is lead used for roofing

Because it can be moulded around joints and corners to provide protection from the rain.

49

Why is Mg used in flares?

Because it burns readily and emits bright, white light.