1. introduction
- 2. Carbon based life forms are made form molecules using carbon atoms A carbon atom has 6 protons 6 neutrons and 6 electrons This gives 4 electrons in the outer shell so a carbon atom will make 4 covalent bonds to have a stable 8 electrons Here carbon (blue) has made a covalent bond with each of 4 hydrogens (red) This makes a molecule called methane with a chemical formula of CH4
- 3. Methane is a 3-dimensional structure like this:
- 4. Which can be drawn like this: Or more simply like this:
- 5. Carbon can share an electron with another carbon, forming a covalent bond Notice that there are now only 3 hydrogen atoms on each carbon CH3CH3 or C2H6 This is ethene
- 6. By forming covalent bonds between carbon atoms long carbon chains can be built Notice that each carbon makes 4 bonds so the terminal carbons have 3 hydrogens, the central ones have 2
- 7. Other atoms like oxygen and nitrogen can also form covalent bonds with carbon Oxygen requires 2 more electrons to form a stable shell so often forms a double bond, sharing 2 electrons with carbon which also shares 2 electrons
- 8. Double Bonds These can form between 2 carbons or between other atoms Each carbon still has 4 bonds, but there are 2 bonds between the carbons So there is only space for 2 hydrogen atoms to attach to each carbon This is Ethylene
- 9. There can even be a triple bond between carbon molecules Notice that sometimes we simply draw a line without showing Hydrogen on the end – it is implied
- 10. Double Bonds can form between carbon and other molecules Or as part of a ring structure
- 11. Functional groups The order in which atoms attach to a carbon chain will determine the properties of the molecule
- 12. Aldehyde group - CHO This attaches to a carbon chain This is a carbonyl group Aldehydes often smell aromatic Acetone and some vitamins are aldehydes
- 13. Keto group - CO A central carbon bonds to oxygen This is another carbonyl group
- 14. Hydroxyl group - OH This attaches to a carbon Molecules with this group are called alcohols Hydroxyl groups are important in making bonds by condensation
- 15. Molecules are named according to the position of the hydroxyl group Hydroxyl is terminal Hydroxyl is in the middle
- 16. Carboxyl group - COOH These are called acids The hydrogen will dissociate and become a proton (H+ ) in solution – making the solution acidic The oxygen left becomes positively charged giving the molecule an overall charge Charged molecules are called polar molecules
- 17. Saturated Carbon chains have no double bonds Unsaturated carbon chains have one or more double bonds and therefore fewer hydrogen molecules
- 18. OPTICAL ISOMERISM This may occur when 2 molecules have the same molecular formula but different arrangements in space, forming mirror images. If a central carbon has FOUR DIFFERENT groups attaches it will be asymmetrical, and may exist in two different forms.
- 19. The central black carbon has 4 different groups attached By rearranging these we can form isomers which are mirror images
- 20. Like a left and a right hand This is important in biology because molecules must fit into enzymes If the shape is wrong it would be like trying to put your left hand into a right-hand glove
- 22. Isomers change the angle of plane-polarised light; Bending it either right or left They are named accordingly
- 23. Molecules are actually based on the properties of the isomers of glyceraldehyde D = right L = left