1. Non-Polar molecules because of covalent nature of C–C and C–H bonds.
2. Physical state – C1 –C4 alkanes are gases, C5 –C17 alkanes are liquids, C18 and above alkanes are solids.
3. Boiling point
- Increases with increase in molecular mass. This is because vander Waals forces increase with increase in surface area. propane < butane < pentane
- Decreases with increase in branching. This is because with increase in branching, molecule acquires the shape of a sphere. As a result the surface area decreases and hence vander Waals forces decrease.
4. Melting Point: Increases with increase in molecular mass though the increase in not regular. It is seen that this increase in melting point is more when we go from an alkane having odd number of carbons to the next higher alkane and is less when we go from an alkane having even number of carbons to the next higher alkane. This is because melting point not only depends on the size but also on the arrangement of the molecule in the crystal lattice. And symmetrical structures fit well into the crystal lattice, are better packed and strongly held and thus possess high melting points.
5. Solubility Alkanes being non polar are insoluble in polar solvents like water and alcohol and are soluble in non polar solvents like benzene, CCI4 . They are also miscible with each other.
6. Density Increases with increasing molecular mass and goes to a maximum of 0.8 g cm-3 . Alkanes being lighter float on water and thus water cannot extinguish fire caused by any alkane.
