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16/07/2014. Alkenes. L.O. I can draw the structural and molecular formula of the first four alkenes. I know the test for alkenes and can use it to identify an alkene from an alkane. C. C. Single covalent bond. C. C. Double covalent bond. Alkenes.

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Alkenes

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16/07/2014

Alkenes

L.O.

  • I can draw the structural and molecular formula of the first four alkenes.

  • I know the test for alkenes and can use it to identify an alkene from an alkane.


C

C

Single covalent bond

C

C

Double covalent bond

Alkenes

  • When carbon forms compounds each carbon atom always forms four bonds.

  • This does not, however, mean that each carbon is joined to four other atoms.

  • It is possible to have bonds grouped into pairs. These are called double bonds.

  • Alkenes contain carbon atoms joined by double covalent bonds.


H

H

C

C

H

H

or

Ethene - formula

  • The simplest alkene is ethene.

  • It has the formula C2H4

  • The carbon atoms are joined together by a double bond.

  • Its displayed formula may be drawn in slightly different forms but should always clearly show the double bond.


16/07/2014

Alkenes Molecular formula Displayed formula

Ethene C2H4 HH

C C

HH

Propene C3H6 HH H

C C C H

HH


16/07/2014

Alkenes Molecular formula Displayed formula

Butene C4H8 HH H H

C C C C H

HH H

Pentene C5H10 HH H H H

C C C C C H

HH HH

What is the general formula for the alkenes? – CnH????


The general formula of the alkenes is

CnH2n


Activity

H

H

H

C

H

C

C

H

H

H

H

H

H

C

H

H

C

H

H

C

H

C

H

H

H

C

C

C

H

H

C

C

H

H

H

H

  • Sometimes the displayed formula is drawn as shown.


Activity

  • What will be the formula for alkenes containing the following numbers of carbons?

C11H22

C13H26

C32H64

C21H42


Saturated or Unsaturated?

  • Alkanes are saturated.

  • Saturated means “full up”.

  • Every carbon atom has already used all four of it’s bonds to join to four other atoms. No other atoms can be added.

  • Alkenes are unsaturated.

  • They have a double bond that could instead become two single bonds. This means that other atoms can be added. It is not “full up”.


Br2

+

Gas red colourless

Bromine water +alkene

Test for Alkenes

When bromine water is added to an

alkane nothing happens

but when bromine is added to an alkene

the red colour of the bromine disappears.

1,2 dibromoethane


Activity

  • Complete the blanks

alkene

C5H10

alkane

C8H18

alkene

C4H8

alkane

C10H22


Which of these is an alkene?

  • C6H14

  • C4H8

  • C12H26

  • C102H206


The formula of the alkene with 15 carbons is?

  • C15H30

  • C15H60

  • C15H32

  • C15H28


Hydrocarbons contain only which two elements?

  • Carbon and electron

  • Carbon and water

  • Carbon and oxygen

  • Carbon and hydrogen


The bonds in a hydrocarbon are what type?

  • Covalent

  • Ionic

  • Complex

  • Metallic


Which is the simplest Alkene?

  • Methene

  • Decene

  • Ethene

  • Butene


Which is alkene has 5 carbons?

  • Propene

  • Pentene

  • Pectane

  • Proptene


What is the molecular formula of Butene?

  • C3H6

  • C4H8

  • C2H4

  • C6H12


What do alkanes do to Bromine water?

  • Produce layers

  • Turn it colourless

  • Leave it unchanged


Bingo

1. Alkanes9. Bromine water

2. Methane10. covalent

3. C2H611. propane

4. Carbon12. colourless

5. Hydrogen13. electron

6. Orange14. C2H4

7. ethene15. alkene

8. Six16. butene


Homework

Complete sheet on the alkenes.


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