Alkanes
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Before reading through this page we recommend recapping on bonding.
Also check out our video section on Alkanes and Alkenes
Alkanes, put simply are hydrocarbons containing a single bond therefore they’re known as being saturated (containing a single bond between carbon atoms).
Also check out our video section on Alkanes and Alkenes
Alkanes, put simply are hydrocarbons containing a single bond therefore they’re known as being saturated (containing a single bond between carbon atoms).
We will start with the first alkane in the series:
Methane
Methane
Carbon has 6 electrons in total 4 of these being on its outer shell (shown as the red dots), therefore it only needs 4 more electrons to be stable. In methane the 4 hydrogen atoms each share their electrons (the blue cross) with 1 of the 4 electrons in the carbon atoms outer shell.
Ethene
Ethene
The alkane in the series is known as Ethane. A single covalent bond is formed between the 2 carbon atoms, with 6 more hydrogen atoms covalently bonded to complete the molecule.
The next 2 molecules in the series are Propane and Butane, now we don't always have to draw the shells and electrons we can represent the alkanes in displayed formula, each line represents a covalent bond.
Propane
The next 2 molecules in the series are Propane and Butane, now we don't always have to draw the shells and electrons we can represent the alkanes in displayed formula, each line represents a covalent bond.
Propane
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Butane
This alkane series continues and follows the general formula:
CnH2n+2
Let’s use ethane as an example using the general formula:
CnH2n+2
Let’s use ethane as an example using the general formula:
n represents 2 for the 2 carbon atoms in ethane, we can see that the number of hydrogens will be:
2x2 = 4
4+2= 6
This tells us that ethane has 6 hydrogens hence we get the molecular formula
C2H6.
We can use this general formula to help us find the molecular formula of other alkanes.
Let’s use pentane
Pentane has 5 carbons so n=5
Find the number of hydrogens using the general formula.
5x2= 10
10 + 2 = 12
Pentane has 12 hydrogen atoms meaning its molecular formula is C5H12
Pentanes displayed formula:
2x2 = 4
4+2= 6
This tells us that ethane has 6 hydrogens hence we get the molecular formula
C2H6.
We can use this general formula to help us find the molecular formula of other alkanes.
Let’s use pentane
Pentane has 5 carbons so n=5
Find the number of hydrogens using the general formula.
5x2= 10
10 + 2 = 12
Pentane has 12 hydrogen atoms meaning its molecular formula is C5H12
Pentanes displayed formula:
Need help drawing alkanes? Attempt the worksheet attached.
| Drawing Alkanes |