Alkanes

• properties of alkanes

  saturated hydrocarbons, containing carbon and hydrogen atoms held together by single covalent bonds
• what bonds join carbons together to other atoms in an alkane?

  sigma bonds - single covalent bonds
• shape of alkanes

  each carbon atom is surrounded by 4 electron pairs in 4 sigma bonds. repulsion in these electron pairs results in a tetrahedral arrangement around each carbon atom with a bond angle of approximately 109.5
• general formula

  CnH2n+2
• boiling point trend

  across the first 10 alkanes, boiling points increase
• why does boiling point increase?

  increased chain length, greater surface area of contact, stronger london forces
• affect of branching on boiling point

  more branching, less surface area of contact, weaker london forces
• reactivity

  alkanes do not react with most common reagents
• reasons of lack of reactivity of alkanes

  C-C and C-H sigma bonds are strong

  C-C bonds are non polar

  electronegativity of carbon and hydrogen are so similar that C-H bonds are considered non polar
• complete combustion of alkanes

  as you descend the homologous series, each alkane molecule (CH2) needs an extra 1.5 O2 molecules for complete combustion
• combustion of alkanes

  CnH2n+2 + O2 -> CO2 + H2O
• reactions of alkanes and halogens

  presence of high energy ultraviolet radiation in sunlight provides the initial energy for the reaction to take place