Organic molecules
Carbon forms a huge variety of both synthetic and natural molecules. These organic molecules have a structure based upon carbon chains and/or carbon rings. A 'family' of organic compoundCompounds that contain carbon atoms, joined by covalent bonds to other atoms (including other carbon atoms). with the same functional groupAn atom, or group of atoms, that determines the main chemical properties of an organic compound. is called a homologous seriesA 'family' of organic compounds that have the same functional group and similar chemical properties. .
The properties of organic molecules depend on their structure being made of simple moleculeA collection of two or more atoms held together by chemical bonds.. The atoms in an individual molecule are joined together by strong covalent bondA bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.. The intermolecular forcesWeak attractive forces between molecules. When a simple molecular substance melts or boils, it is the intermolecular forces that are broken (not the covalent bonds in each molecule). between molecules are weaker.
The intermolecular forces vary between molecules, so different organic compounds have different melting points and boiling points.
Simple molecular substances have no overall charge, and their electronSubatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. are not free to move. So these substances are poor conductors of electricity and heat.
Polymers
polymerA large molecule formed from many identical smaller molecules known as monomers. consist of very long molecules that contain chains of carbon. They too are held together by very strong covalent bonds. There are greater intermolecular forces between the long chains compared with smaller simple molecules. This means that polymers have a higher melting point than many other organic molecules.
The intermolecular forces affect:
- hardness
- melting point
- behaviour on heating (whether the polymer returns easily to shape after heating)
- flexibility