Alkenes
The Unsaturated hydrocarbon with a double bond between the carbon atoms. form a A 'family' of organic compounds that have the same functional group and similar chemical properties. . Like all homologous series, the alkenes:
- have the same An algebraic formula that sets out a rule or trend which is followed by all members of a homologous series. For example, all non-cyclic alkanes have the general formula CnH2n+2.
- differ by CH2 in Chemical formula showing the actual number of atoms of each element in a molecule. from neighbouring A substance formed by the chemical union of two or more elements.
- show a gradual variation in A description of the appearance of a substance or how it acts without involving chemical reactions. For example, state, melting point, conductivity, etc., such as their The temperature at which a substance rapidly changes from a liquid to a gas.
- have similar A description of how a substance reacts with other substances. For example, flammability, pH, reaction with acid, etc.
General formula
The general formula for the alkenes is CnH2n (where n is the number of carbon atoms in the molecule).
Worked example
Decene is an alkene. Its A collection of two or more atoms held together by chemical bonds. contain ten carbon The smallest part of an element that can exist.. Predict the molecular formula of decene and explain your answer.
The formula will be C10H20. This is because n = 10. So, 2n = (2 × 10) = 20.
Question
Hexene is an alkene. Its molecules contain six carbon atoms. Predict the molecular formula of hexene.
The formula will be C6H12.
Structures
The table shows four alkenes, their molecular formulae and their structures.
Notice that butene has two different forms called Chemicals that have the same molecular formula but different arrangements of atoms. . But-1-ene and but-2-ene have the same molecular formula, but the position of their C=C bond is different. The number in their names show where that bond is located in the molecule.
The alkenes are unsaturated hydrocarbons:
- A compound that contains hydrogen and carbon only., because they are compounds containing hydrogen and carbon only
- An unsaturated compound contains at least one double or triple bond., because they contain a C=C double bond
The C=C bond is the An atom, or group of atoms, that determines the main chemical properties of an organic compound. in the alkenes. It is responsible for the typical reactions of alkenes.
