Elements are the basic building blocks of everything.
Some elements are metals, such as iron, copper, and gold. Others are non-metals, such as oxygen, sulphur, and carbon.
They behave differently.
Metals are usually:
Shiny
Hard
Strong
Malleable
Ductile
Good conductors of heat and electricity
Sonorous
Metals usually shine when their surface is clean.
This shine is called metallic lustre.
Gold, silver, and copper are examples.
Malleability means a metal can be beaten into thin sheets.
Gold is very malleable, so it can be made into extremely thin gold leaf.
Ductility means a metal can be pulled into wires.
Copper and aluminium are made into wires because they are ductile and conduct electricity well.
Metals allow heat and electricity to pass through them.
Copper is used in electrical wires. Aluminium is used in cooking utensils and some wires.
Metals make a ringing sound when struck.
That is why bells are made from metals.
Non-metals are usually:
Dull
Brittle
Not malleable
Not ductile
Poor conductors of heat
Poor conductors of electricity
Not sonorous
Some elements do not follow the usual rules.
Mercury is a liquid metal.
Sodium and potassium are soft metals.
Iodine is a shiny non-metal.
Diamond is a very hard non-metal.
Graphite is a non-metal that conducts electricity.
Metals react with oxygen to form metal oxides.
[ \text{Metal}+\text{Oxygen}\rightarrow\text{Metal oxide} ]
Example:
[ 2Mg+O_2\rightarrow2MgO ]
Magnesium burns with a bright white flame and forms magnesium oxide.
Most metal oxides are basic.
A basic substance can turn red litmus paper blue.
Some metal oxides are amphoteric, which means they can act like both acids and bases.
Examples:
Aluminium oxide
Zinc oxide
Some metals react with water to form a metal hydroxide and hydrogen gas.
[ \text{Metal}+\text{Water}\rightarrow\text{Metal hydroxide}+\text{Hydrogen} ]
Different metals react differently:
Potassium and sodium react very violently.
Calcium reacts less violently.
Magnesium reacts with hot water.
Iron reacts with steam.
Copper, silver, and gold do not react with water.
Sodium reacts very quickly with air and water.
It can catch fire.
Kerosene keeps sodium away from air and water, so sodium is stored under kerosene.
Many metals react with dilute acids to produce salt and hydrogen gas.
[ \text{Metal}+\text{Acid}\rightarrow\text{Salt}+\text{Hydrogen} ]
Example:
[ Zn+2HCl\rightarrow ZnCl_2+H_2 ]
The bubbles are hydrogen gas.
Hydrogen burns with a pop sound.
A more reactive metal can remove a less reactive metal from its compound.
Example:
[ Fe+CuSO_4\rightarrow FeSO_4+Cu ]
Iron is more reactive than copper, so iron pushes copper out of copper sulphate.
This is called a displacement reaction.
The reactivity series arranges metals from most reactive to least reactive:
[ K>Na>Ca>Mg>Al>Zn>Fe>Pb>H>Cu>Hg>Ag>Au ]
Metals near the top react easily.
Metals near the bottom react slowly or hardly react.
Metals usually lose electrons and become positive ions.
Example:
[ Na\rightarrow Na^+ + e^- ]
Non-metals usually gain electrons and become negative ions.
Example:
[ Cl+e^-\rightarrow Cl^- ]
When a metal gives electrons to a non-metal, they form an ionic compound.
Example:
Sodium gives one electron to chlorine.
Sodium becomes (Na^+).
Chlorine becomes (Cl^-).
Together they form sodium chloride, (NaCl).
The positive and negative ions pull toward each other.
Ionic compounds are usually:
Hard
Brittle
Solids
High-melting
Soluble in water
They conduct electricity when:
Melted
Dissolved in water
They do not conduct electricity as solids because their ions cannot move.
Minerals are natural substances found in Earth’s crust.
Some minerals contain metals.
An ore is a mineral from which a metal can be extracted conveniently and profitably.
For example, some iron minerals are ores of iron.
Ores contain unwanted materials such as:
Sand
Soil
Rock
These impurities are called gangue.
Gangue is removed before the metal is extracted.
Extracting a metal means taking it out of its ore.
The method depends on how reactive the metal is:
Low-reactivity metals can often be obtained by heating.
Medium-reactivity metals are obtained by reducing their oxides.
Highly reactive metals are obtained by electrolysis.
Metals such as gold and silver are not very reactive.
They may be found naturally as free metals.
Some of their compounds can be changed into metals just by heating.
Metals such as zinc, iron, lead, and copper are moderately reactive.
Their ores are first changed into metal oxides.
Then oxygen is removed from the oxide.
Removing oxygen is called reduction.
Roasting means heating a sulphide ore in plenty of air.
It changes the sulphide into an oxide.
[ 2ZnS+3O_2\rightarrow2ZnO+2SO_2 ]
Calcination means heating a carbonate ore with little or no air.
It changes the carbonate into an oxide.
[ ZnCO_3\rightarrow ZnO+CO_2 ]
Carbon can remove oxygen from some metal oxides.
Example:
[ ZnO+C\rightarrow Zn+CO ]
The metal is left behind.
Aluminium can remove oxygen from iron oxide.
This makes molten iron and a lot of heat.
[ Fe_2O_3+2Al\rightarrow2Fe+Al_2O_3+\text{heat} ]
This reaction is used to join railway tracks.
Metals such as sodium, magnesium, calcium, and aluminium are very reactive.
Carbon cannot remove oxygen from their compounds.
They are extracted using electricity. This is called electrolysis.
The metal extracted from an ore may still contain impurities.
Removing these impurities is called refining.
In electrolytic refining:
The impure metal is connected to the positive side.
A pure strip of metal is connected to the negative side.
The solution contains the metal compound.
Electricity moves pure metal onto the pure strip.
The impurities settle at the bottom as anode mud.
Corrosion means a metal slowly gets damaged by air, water, or chemicals.
Examples:
Iron rusts.
Silver turns black.
Copper develops a green coating.
Iron rusts when it comes into contact with both:
Oxygen
Water
The brown substance formed is called rust.
Rusting can be prevented by stopping air and water from touching the metal.
Methods include:
Painting
Oiling
Greasing
Galvanising
Chrome plating
Anodising
Making alloys
Galvanisation means coating iron with zinc.
The zinc layer protects the iron from air and water.
Zinc also helps protect exposed iron if the coating is scratched.
An alloy is a mixture of metals, or a mixture of a metal and a non-metal.
Examples:
Brass = copper + zinc
Bronze = copper + tin
Steel = iron + carbon
Stainless steel = iron + chromium + nickel
Solder = lead + tin
Alloys are often stronger or more useful than pure metals.
Pure gold is very soft.
Silver or copper is mixed with it to make it harder and more suitable for jewellery.
Aluminium reacts with oxygen and forms a thin layer of aluminium oxide.
This layer protects the aluminium underneath.
Copper is a good conductor and does not react easily with water.
It is therefore useful for pipes and electrical wires.
Tin is less reactive than iron.
The tin coating stops the iron can from reacting with food.
Copper can get a dull layer on its surface.
Lemon contains acid, which reacts with and removes this layer.
The copper becomes shiny again.
Metals are usually shiny, strong, malleable, ductile, and good conductors.
Non-metals are usually dull, brittle, and poor conductors.
Metals can react with oxygen, water, acids, and salt solutions.
More reactive metals can displace less reactive metals.
Metals form positive ions, while non-metals form negative ions.
Metals are extracted from ores.
Corrosion damages metals, but painting, galvanising, and alloys help protect them.