Hydrocarbons

1
Hydrocarbons
04/10/2014

• L.O.
• I know what a hydrocarbon is and can name and
  draw the structural and molecular formula of the
  first six alkanes.

2
Carbon Organic Chemistry

• Carbon is an unusual atom in that it is able to
  form very strong covalent bonds with other carbon
  atoms.
• When we then include its ability to also bond
  with other elements we open up the possibility of
  the highly diverse and complex molecules (like
  DNA) that have led to the possibility of life.
• Because of this, the chemistry of carbon
  containing compounds is often called organic
  chemistry.

3
Alkanes

• A hydrocarbon consists of carbon and hydrogen
  only and every carbon has four single covalent
  bonds.
• The simplest hydrocarbons form a series of
  compounds known as the alkanes.

4
Formulae and Models of Alkanes

• Although normal chemical formula - like C5H12 -
  are used to describe alkanes they do not convey
  which atom is joined to which other atom.
• To get around this we often used displayed
  formula to describe organic molecules.
• Displayed formula show which 4 atoms each carbon
  is bonded to but even these do not show the
  actual 3D shapes. For that we use models.

methane, CH4
5

• Copy and complete the following table but make
  the displayed formula the 3rd column.

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Displayed formula Alkane Molecular
formula






7






8



Notice the carbon chain is not really straight
and so on
9

• The names of the 4 simplest alkanes are methane,
  ethane, propane and butane.
• After that the names are systematic (like the
  words used to describe geometric shapes.) e.g.
• 5 carbons pentane C5H12
• 6 carbons hexane C6H14
• 7 carbons heptane C7H16
• 8 carbons octane C8H18
• 9 carbons nonane C9H20
• 10 carbons decane C10H22
• Work out a general formula for the alkanes e.g.
  Cn H ????

10

• The general formula of the alkanes is
• CnH2n2

11

• In the backs of your books-
• Come up with an Mnemonic to remember the first 6
  alkanes
• e.g. My very easy method just speeds up naming
  planets.

Michael Eats Pizza But Prefers Hash-browns
12
Activity

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

Number of carbons Formula
12
16
31
19
C12H26
C16H34
C31H64
C19H40
13
Bonding in Alkanes
Alkanes contain atoms held together by single
covalent bonds. In the formula displayed we
show these bonds as a single line. Each line
is really a pair of shared electrons
14

• Which of these is an alkane?
• C6H14
• C4H8
• C12H24
• C102H204

15

• The formula of the alkane with 15 carbons is?
• C15H30
• C15H60
• C15H32
• C15H28

16

• Hydrocarbons contain only which two elements?
• Carbon and electron
• Carbon and water
• Carbon and hydrogen
• Carbon and oxygen

17

• The bonds in a hydrocarbon are what type?
• Metallic
• Ionic
• Complex
• Covalent

18

• Which is the simplest hydrocarbon?
• Methane
• Decane
• Ethane
• Butane

19

• Which is alkane has 6 carbons?
• Heptane
• Hexane
• Hectane
• Hoptane

20

• What is the molecular formula of ethane?
• C3H8
• C4H10
• C2H6
• C6H14

21

• How many carbons does propane have?
• 6
• 3
• 2
• 5

22
Bingo

• 1. Alkanes 9. butane
• 2. Methane 10. covalent
• 3. C2H6 11. propane
• 4. Carbon 12. ethane
• 5. Hydrogen 13. electron
• 6. Four 14. one
• 7. Three 15. two
• 8. Six 16. five

23
Homework

• Complete sheet on the alkanes.