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Common elements
There are about 100 elements in total, although only about 20
are in everyday use.
An element is the simplest of all chemical substances.
It is made up of only one kind of atom and cannot be decomposed.
A MOLECULE is formed when two or more atoms join together.
Two (or more) elements can combine together to form a compound.
A compound must be made of at least two elements chemically joined together.
eg| magnesium + oxygen
----> magnesium oxide (element) (element) (compound) |
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Click
here for a complete list of elements This list can be sorted into order of density, boiling
point etc)
Click here for a compete list of elements This
list has links
to lots of additional information about each
Some common compounds
Carbon dioxide C02
Copper oxide
CuO
Copper Sulphate CuSO4
Copper carbonate CuCO3
Magnesium oxide MgO
Salt (sodium chloride) NaCl
Sulphur dioxide SO2
Water
H2O
Zinc oxide
ZnO
Some differences between a metallic and non-metallic element:
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Metal |
Non-metal |
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Malleable |
Brittle |
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Conducts electricity |
Does not conduct electricity (except carbon, which does conduct) |
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High melting point (usually solid) |
Low melting point (usually gas or liquid) |
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The oxides of a metal, when soluble, form an alkaline solution. |
The oxides of a non-metalusually form an acidic solution. |
Elements, Mixtures and Compounds: Summary
A substance is an element if it contains only a single kind of atom and can NEVER be decomposed. eg copper, oxygen, carbon, iron, sulphur, zinc, gold
A substance is a compound if it contains more then one element chemically joined together.
eg water, magnesium oxide, copper sulphate, calcium carbonate, cobalt chloride, petrol
A mixture exists when there are at least two substances present (either elements, compounds or a combination of the two).
These two substances are not chemically joined and can often be easily separated.
eg air, ink, orange juice, wood, salty water
The main differences between a compound and mixture are summarized in the table below:|
Mixture |
Compound |
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A mixture contains two or more substances NOT chemically joined. |
Contains at least two elements chemically joined together |
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The different substances may be visible and the appearance may not be uniform |
Will look uniform in appearance (ie the same all the way through). |
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The substances can often be easily separated eg by filtration, evaporation, distillation, chromatography, using a magnet or a separating funnel. |
The elements in a compound cannot be separated without a chemical change. ie a new substance will always be formed. |
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The substances can be mixed in any proportion. |
The elements in a compound are always present in a fixed proportion. |
Although there are over 100 elements, only about 9 of them appear in any quantity in the Earth's crust.
Obtaining metals from their ores
IRON
Iron is obtained by heating the ore with coke.
Iron ore contains iron oxide and coke contains carbon and is made by heating coal.
The carbon in the coke pulls away the oxygen from the iron ore, leaving molten iron.
[Note: other elements, eg zinc, could be used to reduce the iron, but they are expensive and the iron is more difficult to purify after].
Word equation:
Iron oxide + carbon ----> Iron + carbon dioxide
ALUMINIUM
Aluminium is too high in the activity series to be reduced by heating it with carbon.
Aluminium is obtained by a process called electrolysis, where an electric current is passed through the molten ore. This makes aluminium a lot more expensive than iron.
COPPER
Copper is low in the activity (and can be found native as the free metal) but is usually obtained by heating its ore with carbon.
Copper is purified by electrolysis which makes it an expensive metal.
NEW WORDS:
Ore: A rock containing a metal. In most ores the metal is only present as a compound and needs to be refined in some way. Some ores containing unreactive metals, eg copper and gold, can contain the actual metal. A rock containing a metal. In most ores the metal is only present as a compound and needs to be refined in some way. Some ores containing unreactive metals, eg copper and gold, can contain the actual metal.
Electrolysis: The process of passing electricity through a liquid. This can cause the elements in the liquid to separate. Metals are formed on the cathode (negative electrode)
Properties of some common metals| Metal | Advantage | Disadvantage | Use |
| Iron | Cheap, strong | Corrodes easily (rusts), heavy | Girders, bicycle frames |
| Aluminium | low density (light), can be hammered into thin sheets. | A little brittle, expensive | Aircraft bodies, kitchen foil, saucepans and many alloys |
| Copper | Malleable. Good conductor of heat and electricity. | Expensive, not very strong | Water pipes, electric wires. |
| Gold | Does not corrode. Attractive. Good conductor of electricity | Expensive, heavy | Electrical contacts.
Jewellery and ornaments. |
Note: An ALLOY is a mixture containing more than one metal. Eg brass is an alloy of copper and zinc