Alkanes

• A hydrocarbon is a compound containing hydrogen and carbon only.
• Saturated compounds contain only single bonds.
• A homologous series is a series of organic compounds having the same functional group but with each successive member differing by CH₂.
• A structural isomer has the same molecule formula but a different structural formula.
• A radical is a species with an unpaired electron.
• A substitution reaction is a reaction in which an atom or group of atoms is replaced with another atom or group of atoms.
• Homolytic fission is the breaking of a covalent bond where the shared pair of electrons are split equally forming two radicals.
• Alkanes are the main components of natural gas and crude oil.
• Alkanes are amongst the most stable organic compounds.
• Alkanes are mainly used as fuels as they react with O₂ to generate heat.
• Alkanes are joined by a type of covalent bond called a sigma bond, which is the result of direct overlap of orbitals.
• How is a sigma bond formed?

  As a result of direct overlap of orbitals.
• Alkanes are tetrahedral with a bond angle of 109.5 degrees.
• The shapes of alkanes are not rigid; the sigma bond acts as axes around which the atoms can rotate freely.
• The boiling points of alkanes increase as the chain gets longer. This is because as the chain length increases, so does the surface area, resulting in more possible surface contact between molecules.
• If an alkane has more branches, there are less points of surface contact and fewer London forces, resulting in a lower boiling point.
• State the shape and bond angle around the carbon atom in methane. Explain your answer.


  Tetrahedral - 109.5 degrees.

  It has 4 bond pairs and 0 lone pairs. All electron pairs repel, lone pairs repel more.
• State and explain the type of bond between carbon and hydrogen atom.

  A covalent sigma bond - direct overlap of orbitals and a shared pair of electrons between the two atoms allows free rotation about the sigma bond.
• Alkanes are saturated hydrocarbons.
• The electronegativities of carbon and hydrogen are very similar so the C-H sigma bonds are non-polar.
• Because the C-H sigma bonds are non-polar, alkanes are non-polar molecules and have no partial positive or negative charges.
• Alkanes do not react with polar reagents because the C-H sigma bonds are non-polar, meaning alkanes are non-polar molecules and have no partial positive or negative charges.
• Alkanes have no electron-deficient areas to attract nucleophiles, and also lack electron-rich areas to attract electrophiles.
• When more than one alkyl group is identified on the main chain, these are listed alphabetically and di, tri, and tetra are used for 2, 3, and 4.
• London forces increase as the size of the molecules increase.
• Explain why alkanes are insoluble in water.


  They don't react with polar reagents as alkanes are non-polar molecules due to the electronegativities of carbon and hydrogen being so similar.