Alkane Use: Components of natural gas and crude oil.
• Sigma Bond: The type of covalent bonds in alkanes are called sigma bond- It is overlapping of two
orbitals, one from each bonding atom. Positioned on line directly between bonding atoms. Each
carbon atom in alkane has four sigma bonds.
• Shape of Alkanes: Repulsion between the four electron pairs results in tetrahedral arrangement.
• Fractional Distillation: Crude oil separated into fractions of alkanes by fractional distillation,
because hydrocarbons have different boiling points.
• C6H14 is liquid in standard state.
• Cracking: Process used to convert long chain alkanes into more useful shorter alkenes. Cracking
an alkane forms an alkene and alkane.
• Have in molecular formula and not structural if question involves cracking.
• Chain Length:
– As chain length increases or more carbons
– So more surface area of contact between molecules.
– London forces will be stronger as they act when molecules in close surface contact.
– More energy required to overcome London Forces.
• Branching:
– Less surface contact between molecules of branched alkanes compared to straight chain.
– So weaker London forces.
– So less energy needed to break London Forces.
– Also the branches prevent molecules getting as close together, decreasing London forces
further.
• Branched chains have more efficient combustion than straight chains.
• C6H14 -> C6H12 + H2. Formation of cycloalkane from alkane. Also forms a hydrogen. This is done as
cyclohexane promotes efficient combustion.
• Carbon- carbon bonds can break anywhere in the chain so variety of alkanes and alkenes formed
with different chain lengths.
• Cyclopropane + Bromine = 1,3 bromopropane.