Physical Properties of Alkanes

Physical state at room temperature follows chain length: C1-C4 are gases, C5-C17 are liquids, and C18 and above are solids. Alkanes are insoluble in water but soluble in non-polar solvents; being less dense than water, they float on top of it. Boiling point: the boiling point of a continuous (straight) chain alkane rises with chain length, roughly 30 degC for every added carbon, because alkanes are non-polar and held together only by weak Van der Waals forces that depend on molecular surface area and so increase with molecular size; for a given number of carbons, a straight-chain isomer has a higher boiling point than its branched isomers, since branching makes the molecule more compact and reduces the area of intermolecular contact. Solubility and density: since water is polar and alkanes are non-polar, alkanes are insoluble in water -- a property that makes them good water-repellents pr …