Metals

1. Properties of metals Metals are solids that

o Have high melting and boiling points / high densities Held together by strong metallic bonds

o Are malleable, soft and ductile Atoms are packed regularly in layers, that can side over each other

easilyo Good conductors of heat and electricity

There are mobile electrons Alloys are a mixture of a metal with another element

o Bronze = copper and tino Brass = copper and zinco Stainless steel = iron chromium, nickel and carbon

Pure metals have their atoms in a regular arrangement. Alloys have foreign atoms in their structure

Alloys areo Stronger than it constituents (harder and less malleable)

The foreign atoms in the structure makes it harder for the layers of atoms of side over each other

o More attractive Pewter is an alloy of tin, antimony and copper More attractive than pure tin

o More resistant to corrosion Pure copper corrodes easily, its alloy doesn’t. (copper coins)

o Used to lower melting points Solder is an alloy of tin and lead. Used to join metals due to its low melting point, lower than pure

tin/lead

2. Reactivity series

Metal Add cold water Add hot steam Add dilute HCl Carbon reduction

Hydrogen reduction

Potassium Violently, KOH and H2

produced, lilac flame as well Dangerous

to conduct

Explosive reaction

Sodium Violently, NaOH and H2

Calcium Reacts readily, Violently, CaCl2

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Ca(OH)2 and H2 and H2 Cannot be reduced

Cannot be reducedMagnesium Very slowly,

Mg(OH)2 and H2

Violently, MgO and H2, with bright white

glow

Rapidly, MgCl2

and H2

Carbon

No reaction

Zinc Reacts readily, ZnO and H2,

ZnO is yellow when hot,

white when cold

Moderately fast, ZnCl2 and

H2

Can be reduced

Iron Slowly, Fe3O4

and H2, red-hot iron needed

Slowly, FeCl2

and H2

Heated oxides can

be reduced

Lead

No reaction No reaction

HydrogenCopperSilver Reduced

simply by heating

Gold Found as pure gold in earth

The reactivity of the metals are based on their tendency to form positive ionso A more reactive metal would displace a less reactive metal from their solution

The more reactive the metal, the greater the tendency to from ionso A more reactive metal would displace a less reactive metal from their oxides

The more reactive the metal, the more readily it forms compounds Thermal decomposition

o The more reactive the metal, the more stable the compounds it forms, the harder it is to be decomposed

o Potassium and sodium compound cannot be thermally decomposedo Calcium - Copper can be thermally decomposed, forming metal oxide and CO2

o Silver is so unreactive that it decomposes to from silver and CO2

3. Extraction of metals Metals must first be mined, then concentrated, then reduced then refined to give pure

metals The more reactive the metal, the harder is it to extract the metal from its ore Potassium – Magnesium = electrolysis Zinc – Silver = carbon reduction Gold = found naturally uncombined in the earth

4. Recycling of metals Metals are a finite resource, hence we need to recycle them to prevent depletion

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Social impacto Recycling produces less poisonous waste than extractiono Recycling reduces the land taken up by miningo However, it will take time and effort for communities and businesses to practice

recycling as a way of life Economic impact

o It can be more costly to recycle metals Money is spent on transport, sorting and cleaning of metals Thus companies find recycling not worth while

Environmental impacto With recycling, there will be less need to dig for metal ores

Less land is taken up, more can be used for other stuff (agriculture) Less air and water pollution Less landfills for waste materials needed Less fossil fuels used in extraction

5. Iron Blast furnace

o Iron is extracted from haematite, in the blast furnaceo Haematite, coke and limestone is added from the top of the furnace, hot air

from bottom.o Carbon is first combusted to CO2 then reduced to CO due to excess coke

C + O2 CO2, CO2 + C 2 COo Limestone is decomposed and impurities removed, forming slag

CaCO3 CaO + CO2, CaO + SiO2 CaSiO3

o Haematite is reduced to iron Fe2O3 + 3 CO 2Fe + 3 CO2

o Slag floats on molten (impure) iron Steel alloys

o Steel is an alloy of iron with carbon and/or other metals

Steel Components Uses Special propertiesLow carbon steel

(mild steel)Iron, carbon

(up to 0.25%)Car bodies and machinery hard, strong and

malleableHigh carbon steel Iron, carbon

(0.45 – 1.5%)cutting and boring tools strong but brittle

Stainless steel Iron, chromium,

nickel, carbon

equipments in chemical plants, cutlery and surgical

instruments

resistant to corrosion

Rustingo Causes

Caused by presence of oxygen and water, reacting with iron to from hydrated iron(III) oxide

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Acidic substances accelerate the rusting processo Prevention

Protective layer The protective layer prevents water and oxygen from coming

into contact with the iron However, if scratched and iron is exposed, iron will rust. Painting, greasing, plastic coating

Sacrificial protection A metal that is more reactive than iron, magnesium and zinc, is

connected to iron They would corrode preferentially, in place of iron , as they give

electrons to iron However, they require constant replacement

Galvanising It is the coating of iron with a layer of another metal This provides a protective layer, and sacrificial protection, if zinc

or magnesium is used

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