Hydrocarbons
Methane
Methane (CH4) in liquefied natural gas (LNG) is a hydrocarbon.
Methane contains only carbon and hydrogen held together by single covalent bonds. In your notes draw an electron dot diagram for the methane molecule.
Now use this diagram to explain why the methane molecule is a tetrahedral shape.
The four pairs of electrons repel each other equally, and maximise the bond angle between them in order to reduce the repulsion forces.
Ethene
Ethene (C2H4), which is used to make polythene, is a hydrocarbon.
Ethene contains only hydrogen and carbon atoms, with the carbon atoms being held together by a double covalent bond. In your notes draw an electron dot diagram for the ethene molecule.
Now use this diagram to explain why the ethene molecule is a planar molecule and the bond angles around each carbon atom are 120°.
Each carbon atom has one double bond and two single bonds. This gives a total of three charge clouds, which results in the trigonal planar arrangement of bonds around each carbon atom.
This is a very quick reminder of hydrocarbons, including some aspects of bonding and shapes of molecules from Chemistry Unit 3A. You should, of course, have realised that the two molecules shown are the two simplest examples from the groups of hydrocarbons called alkanes and alkenes.
- Do you need to revise the areas of covalent bonding and shapes of molecules?
- You should also revisit your work on alkanes and alkenes.
