CAL PROPERTIES OF ALKANES:-→ Alkanes are almost non-polar molecules because of the covalent nature of C-C and C-H bonds and due to very little difference of electronegativity between carbon and hydrogen atoms. → They posses weak van DER Waals FORCES. Due to the weak forces, the first FOUR members, C1 to C4 are gases, C5 to C are liquids and those containing 18 carbon atoms or more are solids at 298 K.→ They are colourless and odourless. Petrol is mixture of hydrocarbons and is used as a fuel for automobiles.→ Petrol and lower fractions of petroleum are also used for dry cleaning of clothes to remove grease stains.→ It is non-polar and, hence hydrophobic in nature. It is GENERALLY observed that in relation to solubility of SUBSTANCES in solvents, polar substances are soluble in polar solvents, whereas the non-polar ones in non-polar solvents i.e., like dissolves like.→ Boiling point of different alkanes are given in table from which it is clear that there is a steady increase in boiling point with increase in molecular mass. → This is due to the fact that the intermolecular van der Waals forces increase with increase of molecular size or the surface area of the molecule.