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Organic Chemistry

Organic Chemistry. Properties 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.

jeremy-good
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Organic Chemistry

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  1. Organic Chemistry Properties of compounds

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

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