Alkane
Alkanes are chemical compounds that consist only of the elements carbon (C) and hydrogen (H) (i.e., hydrocarbons), wherein these atoms are linked together exclusively by single bonds (i.e., they are saturated compounds). 
In general, the number of carbon atoms is often used to define the size of the alkane (e.g., C2-alkane).
An alkyl group, generally abbreviated with the symbol R, is a functional group or side-chain that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms.
The simplest possible alkane (the parent molecule) is methane, CH4. There is no limit to the number of carbon atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydrocarbon. 
Alkanes are not very reactive and have little biological activity. Alkanes can be viewed as a molecular tree upon which can be hung the interesting biologically active/reactive portions (functional groups) of the molecule.
Structure classification
Saturated hydrocarbons can be:
•	linear (general formula CnH2n + 2) wherein the carbon atoms are joined in a snake-like structure
•	branched (general formula CnH2n + 2, n > 3) wherein the carbon backbone splits off in one or more directions
•	cyclic (general formula CnH2n, n > 2) wherein the carbon backbone is linked so as to form a loop.
Physical properties
Boiling point
Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C.
Alkanes experience inter-molecular van der Waals forces. Stronger inter-molecular van der Waals forces give rise to greater boiling points of alkanes.

There are two determinants for the strength of the van der Waals forces:
•	the number of electrons surrounding the molecule, which increases with the alkane's molecular weight
•	the surface area of the molecule
Under standard conditions, from CH4 to C4H10 alkanes are gaseous; from C5H12 to C17H36 they are liquids; and after C18H38 they are solids. As the boiling point of alkanes is primarily determined by weight, it should not be a surprise that the boiling point has almost a linear relationship with the size (molecular weight) of the molecule. As a rule of thumb, the boiling point rises 20 - 30 °C for each carbon added to the chain; this rule applies to other homologous series.
A straight-chain alkane will have a boiling point higher than a branched-chain alkane due to the greater surface area in contact, thus the greater van der Waals forces, between adjacent molecules. 
On the other hand, cycloalkanes tend to have higher boiling points than their linear counterparts due to the locked conformations of the molecules, which give a plane of intermolecular contact.
Melting point
The melting points of the alkanes follow a similar trend to boiling points for the same reason as outlined above. That is, (all other things being equal) the larger the molecule the higher the melting point. 
Chemical properties
In general, alkanes show a relatively low reactivity, because their C bonds are relatively stable and cannot be easily broken. Unlike most other organic compounds, they possess no functional groups.
They react only very poorly with ionic or other polar substances. 
However redox reactions of alkanes, in particular with oxygen and the halogens, are possible as the carbon atoms are in a strongly reduced condition; in the case of methane, the lowest possible oxidation state for carbon (−4) is reached. Reaction with oxygen leads to combustion, with halogens, substitution. 
Reactions with oxygen (combustion reaction)
All alkanes react with oxygen in a combustion reaction, although they become increasingly difficult to ignite as the number of carbon atoms increases. The general equation for complete combustion is:
CnH2n+2 + (1.5n+0.5)O2 → (n+1)H2O + nCO2
For example methane:
CH4 + 1.5O2 → CO + 2H2O

 Reactions with halogens
Alkanes react with halogens in a so-called free radical halogenation reaction. The hydrogen atoms of the alkane are progressively replaced by halogen atoms

           H                                                            Br  
            l                              + Br2  →                 l
CH3 – CH – CH2 – H                             CH3 – CH – CH3     +     CH3 – CH2 – CH2 – Br 

Statistical distribution:   	            	33 %			67 %
Experimental distribution:		97 %			3 %

Experiments have shown that all halogenation produces a mixture of all possible isomers, indicating that all hydrogen atoms are susceptible to reaction. The mixture produced, however, is not a statistical mixture: Secondary and tertiary hydrogen atoms are preferentially replaced due to the greater stability of secondary and tertiary free-radicals. An example can be seen in the monobromination of propane.

 Cracking
Cracking breaks larger molecules into smaller ones. This can be done with a thermal or catalytic method.