Single or double
Two carbons can share one pair of electrons, or two, or three.
Bromine water is an orange-brown liquid. Read the bonds on each card. Will the bromine water lose its colour?
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The rule
A chain of single bonds is saturated. A double or triple bond makes it unsaturated. Bromine water loses its colour at a double or triple bond.
Saturated means it holds every hydrogen its slots allow. Ethane, C₂H₆, is one.
A chain with a double or triple bond is unsaturated. Ethene, C₂H₄, has a double bond. Ethyne, C₂H₂, has a triple bond.
| Bond | Slots used per carbon | Example | Formula |
|---|---|---|---|
| Single | 1 | Ethane | C₂H₆ |
| Double | 2 | Ethene | C₂H₄ |
| Triple | 3 | Ethyne | C₂H₂ |
A teacher adds bromine water. On a saturated chain the colour stays. On an unsaturated chain the colour fades.
Saturated compounds are not very reactive. Unsaturated ones are more reactive. A catalyst speeds up a reaction and is not used up. Unsaturated ones add hydrogen with a nickel catalyst. Nickel is a metal. Vegetable oils are hydrogenated this way: hydrogen is added to them.
With plenty of air, saturated hydrocarbons burn with a clean flame. In the same air, unsaturated ones give a yellow, sooty flame.