ALKANES

What is a hydrocarbon ?
 Hydrocarbons Alkanes Formulas Stock Illustration - Download Image ...Around six million compounds of carbon are already known! Because there are so many, it is helpful to pick out those compounds which have similar structures. One of the simplest types of organic compound is the hydrocarbon.
      The hydrocarbons that we study at this level can be subdivided into two 'families'. Some hydrocarbons are saturated. These molecules contain only single covalent bonds between carbon atoms. Since carbon valency of 4, the bonds  not used in making the chain are linked of hydrogen atoms (see the figure top). No further atoms can be added to molecules of these compounds. This family of saturated hydrocarbons is known as the alkanes.
      Homologous Series: Definition,Properties and Characteristics ...
      Table up gives the names and formulae of the first six members of the series of alkanes. The simplest alkane contains one carbon atom and is called methane. Note that the names of the series of hydrocarbons all end in -ane. The first part of the name (the prefix) tells you the number of atoms in the chain. These prefixes are used consistently in naming organic compounds.
       The formulae given in table are the molecular formulae of the compounds. Each molecule increases by a -CH2- group as the chain gets longer (see the figure on top). Indeed, the formulae of long-chain alkanes can be written showing the number of -CH2- groups in the chain. For example, octane (C8H18) can be written as CH3--(CH2)6--CH3. The formulae of these molecules all fit the general formula CnH2n+2 (where n is the number of carbon atoms present).
       In organic chemistry, the structure of a molecule is also very important. Figure on the top shows the structural formulae of the first eight alkanes in the series. A structural formula shows the bonds between the atoms. As the length of the hydrocarbon chain increases, the strength of the weak forces between the molecules (intermolecular forces or van der Waals' forces) is increased. This shows itself in the increasing boiling points of the members of the series. The melting points and boiling points of the alkanes increase gradually. Under normal conditions, the first four members of the family are gases, and those between C5H12 and C16H34 (which in short are called C5 to C16 alkanes) are liquids. The compounds in the alkanes family with 17 or more carbon atoms are waxy solids.
         
      Every organic compound has three different formulae. The first of these is the empirical formula. This formulae is the simplest possible whole-number ratio of the atoms in a compound; thus for methane it is CH4, but for ethane it is CH3.
       The second formula for any compound, and the most crucial, is the molecular formula. This represents the actual number of atoms present in the molecule; thus for methane it is CH4, for ethane it is C2H6, and so on. 
       The final formula for any compound, and a highly important one, is the structural formula of the molecule of the compound. This formula shows all the atoms in the molecule and how they are bonded together. The structural formulae of the first eight alkanes are shown in the figure on the top.








    

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