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 }Bakelite.
They all prevent electricity from coming into contact with people.
Electricity is important for cooking, heating, lighting, entertainment etc.
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.
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.
Carbon is the exception - it will conduct in the form of graphite (we use it for the electrodes).
When a metal conducts it is the electrons that move through it.
Metals also conduct when liquid as is shown by mercury in the periodic table.
The elements in the Periodic Table can also be classified as conductors and non-conductors.
Metals consist of atoms closely packed together in a regular way.
They have a particular type of bonding which allow them to conduct electricity when solid. The electrons in the outer shells are 'delocalised' and free to move through the arrangement (from atom to atom).
Thus we say - metals consist of an inner core of immobile protons and neutrons in a sea of outer electrons which carry the current and the whole metal is not affected by the current.
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 charge.
Conduction of Electricity by Compounds which Contain a Metal