Additional Science C2 Topic 7

Some elements bond ionically but they can also bond through covalent bonds.

Covalent bonds is sharing an electron rather then taking one.

For example:
Hydrogen H2 has just one electron. They only need one more to have a full first shell. so they often form single covalent bonds with a second Hydrogen. This is shown in a diagram or H-H
Or
Oxygen atoms have 6 on their outer shell they often ionically bond but will also covalently bond with Hydrogen: H-O-H or with carbon O=C=O.

There are two kinds of covalent substance: simple molecular and giant covalant.

Simple Molecular Covalent Substances:
- Atoms form very strong covalent bonds to form small molecules of two or more atoms. But the forces of attraction between the molecules are very weak.
-The result of weak attraction makes the moleculat covanlent substances have very low melting and boiling points.
-Most molecular substances are gasses or liquids at room temperature.
- Dont conduct electricity.

Examples:
Chlorine, Oxygen, Water

The halogens are all simple molecular structures because of their properties. The inter-molecular forces increase in strength down the halogen group you can tell this by the stronger melting and boiling point needed to break them apart.

Pure Carbon forms Giant Covalent Structures rather than molecules.
All the atoms in the structure are bonded by strong covalent bonds so they have high melting and boiling points. For example Diamond and Graphite.

Diamond:
Shiny, Colourless, Clear.
Used for Jewellery.
Each carbon atom forms 4 covalent bonds making a very strong structure.
Diamond doesnt conduct electricity because there are no free electrons.

Graphite:
Black, Opaque, Lustrous ( Kind of shiny )
Each carbon atom forms 3 covalent bonds making sheets of carbon atoms free to slide over each other.
Layers are held together loosely and can be rubbed off this is how a pencil works.
High melting and boiling points.
Lots of spare electrons only 3 out of 4 bonds are used- makes graphite good conductor of electricity.

Carbon can also form Fullerenes. These are molecules of carbon shaped like a hollow ball or a tube.

Each carbon atom forms 3 covalent bonds leaving free electrons that conduct electricity. The smallest fullerene is 'Buckminster Fullerene' which has 60 carbon atoms joined in a ball written as C60. C60 was discovered by chance.

Fullerenes can be joined together to make nanotubes. All the covalent bonds make the nanotubes very strong for their mass. Make stronger but lighter materials for example building. Nanotubes conduct electricity

Conventional Medicines go through rigorous testing
They have to go through years of testing before they are sold. The final stage of this includes a Placebo. To tell if a drug is good or not:
Did the people taking it get better?
Was the sample of people big enough?
How do the results of people given the drug compare to the people not given it?

Alternative Remedies -are not chemical based
Highly diluted natural substances. It is theory based some people believe that it works for them. Doctors find this difficult to accept.