What are Alkanes?
Alkanes are organic compounds that consist of single-bonded carbon and hydrogen atoms. The formula for Alkanes is CnH2n+2, subdivided into three groups – chain alkanes, cycloalkanes, and the branched alkanes.
Alkanes are comprised of a series of compounds that contain carbon and hydrogen atoms with single covalent bonds. This group of compounds consists of carbon and hydrogen atoms with single covalent bonds. Also, comprises of a homologous series having a molecular formula of C nH2n+2
The simple alkane methane contains one carbon atom and CH4 as its molecular formula. As this compound have just single covalent bonds only, therefore, its structural formula is
In a long chain alkane molecule, additional carbon atoms are attached to each other with the help of a single covalent bond. Each atom is attached to the sufficient hydrogen atoms to develop a total of four single covalent bonds. This long-chain structure is known as octane. An eight-carbon alkane has a molecular formula – C 8H 18 and structural formula-
The list of some Alkanes and the molecular formula is given below.
Methane (CH4), Ethane (C2H6), Propane (C3H8), Butane (C4H10), Pentane (C5H12), Hexane (C6H14), Heptane (C7H16), Octane (C8H18), Nonane (C9H20), Decane (C10H22).
Physical Properties of Alkanes
1. The Solubility of Alkanes
- Due to very little difference of electronegativity between carbon and hydrogen and covalent nature of C-C bond or C-H bond, alkanes are generally non-polar molecules.
- As we generally observe, polar molecules are soluble in polar solvents whereas non-polar molecules are soluble in non-polar solvents. Hence, alkanes are hydrophobic in nature that is, alkanes are insoluble in water.
- However, they are soluble in organic solvents as the energy required to overcome the existing Van Der Waals forces and generate new Van Der Waals forces is quite comparable.
2. The Boiling Point of Alkanes
- As the intermolecular Van Der Waals forces increase with the increase of the molecular size or the surface area of the molecule we observe:
- The boiling point of alkanes increases with increasing molecular weight,
- The straight-chain alkanes are observed to have a higher boiling point in comparison to their structural isomers.
3. The Melting Point of Alkanes
- The melting point of alkanes follow the same trend as their boiling point that is, it increases with increase in molecular weight.
- This is attributed to the fact that higher alkanes are solids and it’s difficult to overcome intermolecular forces of attraction between them.
- It is generally observed that even-numbered alkanes have a higher trend in melting point in comparison to odd-numbered alkanes as the even-numbered alkanes pack well in the solid phase, forming a well-organized structure which is difficult to break.
When a substituent like halogen bonds to an alkane molecule, one carbon-hydrogen bond of the molecule gets converted to carbon-substituent bond. It can be understood with an example- A new compound known as chloromethane is formed when methane reacts with chlorine. The new compound is composed of a CH3 group that is bonded to a chlorine atom.
When an alkane having hydrogen is removed from one bond, it is called an alkyl group. This Alkyl group is often denoted by the letter R same as halogens represent by the letter X. Here is a methane‐chlorine reaction that can be generalized as
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