Formula Of Organic Molecules | Organic Chemistry | Chemistry | FuseSchool
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Formula Of Organic Molecules | Organic Chemistry | Chemistry | FuseSchool


In this video you will learn how to use different
types of formula to represent organic molecules. Organic molecules can be shown in a variety
of ways using different types of formula. The formula used most frequently in our videos
has been the “displayed formula”. This is because displayed formula provides to clearest
visual structure of an organic molecule. Here is the molecule butene shown in displayed
formula. It shows all the atoms in the correct order with lines to represent all single and
double covalent bonds. Drawing all the bonds for very common molecules
can be quite repetitive. For example, here is butanoic acid in its displayed formula.
Since this is a common molecule and as chemists we are clear with the bonding arrangement
of the carboxylic acid functional group, we also use structural formula to represent organic
molecules. Here is the structural formula. As you can see the covalent bond between the
OH is not shown as we know this is the arrangement. In fact, we would simplify this further and
remove all the displayed bonds like this… Structural formula is often used when writing
equations but the formula does mean that it isn`t always clear what arrangement bonds
are in. Here is another example – first the displayed formula of propane. If we then
take out the lines representing the covalent bonds and group our atoms together in the
order they are arranged, we make the structural formula of propane.
Pause the video now and try and draw both the displayed formula and structural formula
of pentane which has 5 carbon atoms. Here is the displayed formula of pentane and
here is its structural formula. Molecular formula is another type used and
shows us only the number of each type of atom in the compound. To work out the molecular
formula, you simply add up each type of atoms. For example, here is the displayed formula
for hexane. As you can see, it has 6 carbon atoms and it has 14 hydrogen atoms. The molecular
formula of hexane is therefore C6H14. This alone is not very useful as it does not show
us how the atoms are arranged and where the bonds are. If you look at these molecules,
they all have 6 carbon atoms and 14 hydrogens – although you may not be able to name these
different molecules, you can see they are very different but all have the same molecular
formula This is the molecule glucose. Pause the video
now and complete the molecular formula for glucose.
You should have counted 6 carbon atoms, 12 hydrogen and 6 oxygen atoms so the molecular
formula is C6H12O6. Sometimes the formula is reduced even further
to make an Empirical formula. The empirical formula is the simplest whole number ratio
of atoms in a compound. We need to find the highest common factor, a number that all the
numbers, 6,12,6 will divide into. They will all divide by 6 so if we do this, we get C1,
H2 , O1, we don`t show the 1s and so the empirical formula is CH2O. Although empirical formula
doesn`t show us the molecule or how it is arranged, it does tell us the ratio of atoms
in the molecule! Now at the end of this video, you should understand
how to draw organic molecules in displayed, structural, molecular and empirical formula.

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