Unit 7 chemistry

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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
conducts electricity. An electrical insulator does not allow electrons
to flow through it.
In household circuits copper wires conduct electricity.
Some insulators are: Sockets, Plug Covering and Plastic Wire coating
They all prevent electricity from coming into contact with people.
Electricity is important for cooking, heating, lighting, entertainment
A Build up of Electricity
Opposite charges attract.
Like charges repel.
When plastic material is rubbed on cloth it becomes charged - it
picks up extra electrons from the atoms of the cloth. It has a
negative charge. This build up of charge is called static electricity.
When the charged rod is put close to tiny bits of paper it will pick
them up. The negative charge on the rod repels the negative
particles from atoms of the paper nearest to it. The positive
particles left on the surface are attracted to the negative charge.
When the charged rod is put close to a flow of water it bends the
flow of water due to static electricity.

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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 carbon because it conducts electricity
but it is relatively unreactive.
Metals conduct electricity.
All the elements which do not conduct are non-metals.…read more

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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 consist of molecules which do not have a
[Phosphorus Trichloride].
Conduction of Electricity by Compounds which Contain a Metal
There are many compounds of the type MX, e.g.…read more

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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 a flow of
Covalent Compound (Molecule) Bonding
Charged Particles in Solution
An ion is an atom which has gained or lost electrons (e) from its
outer energy level.…read more

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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 products are
formed. This passage of electricity through the solution is called
electrolysis and the solution between the electrodes, which does
the conducting, is called the electrolyte.…read more

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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.
Another way of freeing the ions from the solid lattice would be to
melt the solid by heating it.
The solid lead iodide does not conduct. The molten lead iodide does
conduct.…read more

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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 white solid/ colourless solution must both be
Coloured ions come from the transition metals.
Most copper compounds are blue/green.…read more

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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.
The positive electrode will attract negative ions. These are the
metallic blue copper, ions from copper chromate. A blue colour
should be seen at the positive electrode.…read more

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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,
Reduction is Gain).
A solvent is the liquid that other substances can be dissolved in.
An aqueous solvent means that water is in the solvent.
A non-aqueous solvent is a solvent other than water.…read more

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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 solids at room temperature to be either covalent or
Difference in Bonding
a) Ionic Compounds.
E.g. Sodium Chloride
Ions in a crystal lattice are held together by strong forces.…read more


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