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In this video you will learn how to use different
types of formula to represent organic molecules.

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Organic molecules can be shown in a variety
of ways using different types of formula.

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The formula used most frequently in our videos
has been the “displayed formula”. This

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is because displayed formula provides to clearest
visual structure of an organic molecule. Here

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is the molecule butene shown in displayed
formula. It shows all the atoms in the correct

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order with lines to represent all single and
double covalent bonds.

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Drawing all the bonds for very common molecules
can be quite repetitive. For example, here

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is butanoic acid in its displayed formula.
Since this is a common molecule and as chemists

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we are clear with the bonding arrangement
of the carboxylic acid functional group, we

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also use structural formula to represent organic
molecules. Here is the structural formula.

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As you can see the covalent bond between the
OH is not shown as we know this is the arrangement.

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In fact, we would simplify this further and
remove all the displayed bonds like this…

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Structural formula is often used when writing
equations but the formula does mean that it

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isn`t always clear what arrangement bonds
are in. Here is another example – first

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the displayed formula of propane. If we then
take out the lines representing the covalent

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bonds and group our atoms together in the
order they are arranged, we make the structural

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formula of propane.
Pause the video now and try and draw both

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the displayed formula and structural formula
of pentane which has 5 carbon atoms.

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Here is the displayed formula of pentane and
here is its structural formula.

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Molecular formula is another type used and
shows us only the number of each type of atom

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in the compound. To work out the molecular
formula, you simply add up each type of atoms.

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For example, here is the displayed formula
for hexane. As you can see, it has 6 carbon

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atoms and it has 14 hydrogen atoms. The molecular
formula of hexane is therefore C6H14. This

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alone is not very useful as it does not show
us how the atoms are arranged and where the

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bonds are. If you look at these molecules,
they all have 6 carbon atoms and 14 hydrogens

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– although you may not be able to name these
different molecules, you can see they are

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very different but all have the same molecular
formula

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This is the molecule glucose. Pause the video
now and complete the molecular formula for

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glucose.
You should have counted 6 carbon atoms, 12

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hydrogen and 6 oxygen atoms so the molecular
formula is C6H12O6.

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Sometimes the formula is reduced even further
to make an Empirical formula. The empirical

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formula is the simplest whole number ratio
of atoms in a compound. We need to find the

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highest common factor, a number that all the
numbers, 6,12,6 will divide into. They will

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all divide by 6 so if we do this, we get C1,
H2 , O1, we don`t show the 1s and so the empirical

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formula is CH2O. Although empirical formula
doesn`t show us the molecule or how it is

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arranged, it does tell us the ratio of atoms
in the molecule!

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Now at the end of this video, you should understand
how to draw organic molecules in displayed,

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structural, molecular and empirical formula.