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 physical The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point., such as their The temperature at which a substance rapidly changes from a liquid to a gas.
- have similar chemical properties
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 10 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 Ă— 10) = 20.
Question
Hexene is an alkene. Its molecules contain 6 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.
The ball and stick models on the right show that the A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons. are not really at angles of 90°, as shown in the structures.
The alkenes are An unsaturated compound contains at least one double or triple bond. hydrocarbons:
- A compound that contains hydrogen and carbon only., because they are compounds containing hydrogen and carbon only
- unsaturated, because they contain a C=C double bond, which means that they have two fewer hydrogen atoms than the corresponding alkane
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.