ORGANIC CHEMISTRY
Organic chemistry is the study of the compounds of carbon. The compounds of carbon constitute the central chemicals of all living things on this planet.
Carbon monoxide, carbon dioxide, carbonates and hydrogen carbonates, though containing carbon, are not regarded as organic compounds.
Comparison of Organic and Inorganic Compounds
Organic |
Inorganic |
1) Organic compounds are formed from only a few elements; C,H,O,N,Cl,S |
1) More than 100 different elements. |
2) There are covalent bonds. |
2) Ionic bonds are basically used. |
3) Gases and volatile liquids and their solids have low melting points. |
3) Non-volatile solids and they have high melting and boiling points. |
4) Have their characteristic color and odor. |
4) Colorless and odorless. |
5) Insoluble in water but soluble in organic solvents. |
5) Soluble in water but insoluble in organic solvents. |
6) Organic reactions are slow and complicated. |
6) Inorganic reactions are fast but simple. |
Uniqueness of Carbon
Carbon forms a very large number of compounds. So far more than 10 million organic molecules were reported. This is far more than the number of compounds of all other elements put together (less than 1 million).
Carbon has this unique property because of the following reasons:
- Each carbon atom can form four single covalent bonds at a time.
- Carbon forms strong single double and triple covalent bonds with itself.
- Carbon forms strong bonds with other elements. Ex: methanol, silicon carbide and chlorofluorocarbons.
- Carbon forms stable long C-C chains, branched chains and rings. For example, polyvinylchloride (PVC) and DNA.
Formulas of Organic Substances
Organic substances can be shown with a variety of formulas. Some of these are:
- Molecular formula: we only write the types and numbers of the atoms.
- Structural formula: all the bonds between the atoms are shown.
- Electronic formula: We can write the electronic formula (Lewis dot structure) by displacing the bonds with a pair of electrons.
C2H6 
Molecular formula Electronic formula Structural Formula
Homology and Homologous Series
We have learned that the number of organic compounds is huge. To study them better, the organic compounds are classified into some groups according to their properties.
A group or family of organic compounds is called a homologous series. Members of a homologous series are called homologs. Compounds within a homologous series, called homologs, show the following characteristics:
- They can be represented by the same general formula.
- They show a gradual change in physical properties with increase in molecular mass.
- They show similar chemical properties due to the same functional group.
- They can be prepared by similar methods.
In general a homologous series is a family of compounds all having the same general formula and each member differs from the next by a -CH2- unit.
Homologous Series |
Functional Group |
Formula |
Example |
Names |
Alkanes |
X |
CnH2n+2 |
CH3-CH3 |
Ethane |
Alkenes |
C=C |
CnH2n |
CH2=CH2 |
Ethene |
Alkynes |
|
CnH2n-2 |
|
Ethyne |
Alcohols |
-OH |
CnH2n+1O |
CH3-CH2-OH |
Ethanol |
Aldehydes |
-COH |
CnH2nO |
CH3-COH |
Ethanal |
Carboxylic (oic) acids |
-COOH |
CnH2nO2 |
CH3-COOH |
Ethanoic acid |
Esters |
-COO- |
CnH2nO2 |
CH3 -COO-CH3 |
Methyl ethanoate |
Classification of Hydrocarbons
Hydrocarbons, as the name implies, are compounds whose molecules contain only carbon and hydrogen atoms.
Hydrocarbons those contain only single bonds between their carbon atoms are said to be saturated.
On the other hand, compounds with multiple bonds (double or triple) between their carbon atoms are unsaturated compounds because they possess fewer than the maximum number of hydrogen atoms.
C2H6 C2H4 C2H2
Saturated Unsaturated Unsaturated