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Unit 7

Unit 7 is spread out into 3 sub-topics, the first two are about the
properties of substances, and the last is about writing formulae.


Electricity is a flow of electrons in a definite direction.

an electrical conductor allows electrons to flow through it - it…

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Conduction of Electricity by Elements

The elements are the substances in the Periodic Table. They can be
divided into metals and non-metals.
Electrodes are made of carbon.

The electrodes are the terminals through which the electric current
enters and leaves the substance being tested.

The electrodes are made of…

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Conduction of Electricity by Covalent Compounds

Covalent bonds link atoms of the elements found on the right side
of the Periodic Table.
These elements are non-metals
Covalent substances in solid form, liquid form and solution are to be
tested for electrical conduction.

Covalent compounds never conduct electricity.
Covalent compounds…

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Metal atoms that allow a flow of electricity using their electrons.
Metallic Bonding
Ionic compounds in solution allow a flow of electricity using their
ions (electrolytes).
Ionic Bonding


Non-metal atoms (except Carbon) do not allow a flow of
Metallic Element Bonding
Covalent compounds (molecules) do not allow…

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The following diagram shows the arrangement of positive and
negative ions in a Sodium chloride crystal.

Colour the Sodium ions yellow

Colour the chloride ions green

Electrolysis of Copper Chloride Solution

When electricity passes through a solution (or melt) containing ions,
reactions take place at each electrode and new…

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Compounds which are made up of ions do not conduct electricity
when they are in the solid state. The ions are not free to move.

When a solid dissolves in water the lattice breaks down and the ions
are free to move about and conduct electricity/ carry the current.…

Page 7

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"It conducts electricity" means different things for metals and

Colours of Compounds

Many ionic compounds are coloured. These compounds dissolve in
water to give coloured solutions.
The colour of an ionic compound comes from the colour of the two
types of ions it contains.
The ions of a…

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Electrolysis is the passage of electricity through an electrolyte
causing it to break up.
Copper ions are blue.
Chromate ions are yellow.
The negative electrode will attract positive ions. These are the
metallic blue copper ions from copper chromate. A blue colour
should be seen at the negative electrode.…

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ions, the equation in the Data booklet must be turned the other
Positive metal ions gain electrons at the negative electrode. This is
Negative non-metal ions lose electrons at the positive electrode.
This is oxidation.

The easiest way to remember this is OILRIG (Oxidation is Loss,

Page 10

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If a compound is a solid at room temperature it may be covalent or

Melting and Boiling Points

Ionic compounds are always solid at room temperature.

Covalent compounds exist as solids, liquids and gases.

All liquids are gases at room temperature are covalent compounds.

It is possible for…


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