Organic ChemistryProperties of compounds

Phases Alkanes – first four gasses, 5 to 17

liquids and more than 17 solids at room temperature.

Alkenes – two to four gasses, 5 to15 liquids and more than 15 are solids at room temperature.

Alkynes – two to four gasses, 5 to 17 liquids and more than 17 solids at room temperature.

Density & Solubility

Alkanes, alkenes and alkynes all have densities less than 1g.cm-1 and are therefore less dense than water.

All three groups consists of non-polar molecules which are very soluble in non-polar solvents like tetrachloromethane and benzene, but insoluble in polar solvents like water.

Boiling points of the alkanes As the number of carbon atoms increase

the longer the organic molecule is. The Van der Waals forces between the

molecules increases as the molecule increases ( more C atoms in chain)

The stronger the Van der Waals forces, the more energy is needed to break these forces and the higher the boiling point.

Melting points of the alkanes

As with boiling points, the melting points of the alkanes increase with an increase in the number of carbon atoms.

The graph is not a smooth increase as with the boiling points.

The boiling and melting points of the alkenes and alkynes also increases as the number of C atoms increases.

Alkanes Alkanes like petrol have a very low

boiling point (it is volatile, explosive, flammable) and evaporates easily.

Volatility is the way in which a liquid changes into vapour. Volatility decreases as the number of C atoms increase

Liquids and gasses have larger volatility and therefore very characteristic smells like for eg. petrol. Solids odourless.

Alcohols

Boiling points increase with an increase in the number of C atoms in chain.

Boiling points of alcohols higher than boiling points of corresponding straight chain alkanes, because of stronger hydrogen bond between alcohol molecules.

Alkylhalides

Alkylhalides have higher melting and boiling points than corresponding alkanes.

Molecules are polar so apart from London forces (Van der Waals force) there are also dipole-dipole forces present which is stronger than only Van der Waals forces.

Carboxylic acids

Molecules are polar. Boiling points relatively higher

than corresponding alcohols. This is caused by the fact that the

molecules are kept together by two hydrogen bonds.

Esters Boiling points similar to that of

corresponding Aldehydes and Ketones.

Molecules are polar and have dipole-dipole as well as Van der Waals forces present, but do not form hydrogen bonds.

Lower boiling points than alcohols and carboxylic acids.