Structure and homologous series
Alkanes are saturated hydrocarbons containing only C–C and C–H single sigma bonds. In open-chain alkanes every carbon has total bond order four and the general formula is CnH2n+2. Around a carbon with four single bonds, the arrangement is approximately tetrahedral with bond angles near 109.5°, so carbon chains are not flat straight lines.
Physical properties
Alkanes are essentially nonpolar. They are insoluble in water but dissolve in many nonpolar solvents. Their boiling points generally rise with chain length because dispersion forces become stronger. Among isomers with the same formula, greater branching usually lowers boiling point by reducing effective surface contact. Lower homologues are gases, intermediate members are liquids and larger members are waxy solids under ordinary conditions, though exact boundaries depend on temperature and pressure.