1. Organic chemistry
Mr G Davies S20

2. Organic Chemistry Ridiculously long link:
I have set up a Chemistry Folder which I will populate with resources as we go on (this will include; course break specification, lesson resources, helpful worksheets etc.)
Ridiculously long link:

3. Organic formulae
C2.4
Organic Compounds

4. What is organic chemistry?
Organic chemistry is the study of carbon compounds.
Carbon can form rings and long chains which can sometimes be branched.

5. ALKENES AND ALKANES
Both of these groups of molecules are hydrocarbons. Hydrocarbon – Molecules that contain only the elements carbon and hydrogen. They have the general formulas: Alkanes: CnH2n+2 Alkenes: CnH2n

6. Formulae Of organic compounds
Formulae are ways to show what elements and how many atoms of each element are in a compound.
There are 4 main types of formulae that you need to be aware of:
Molecular
Structural
Displayed
Empirical

7. Molecular formula
If you were given the formula C2H6, what would this molecule look like? Have a go at drawing it.
Now try C4H8Br2 – what would this molecule look like?
The molecular formula tells you the number of atoms of each element in a molecule but cannot tell us how the elements are arranged.

8. Shortened (Structural) Formula
The structural formula tells you both the number of atoms in a compound and the elements, but also shows how the atoms are arranged.
E.g.
Ethane CH3CH3
1, 4-dibromobutane BrCH2CH2CH2CH2Br
Branches in chains are shown in brackets.
E.g. CH3CH(CH3)CH3

9. Displayed Formula
The displayed formula shows how all the atoms arranged and all of the bonds between them.
E.g

10. Skeletal formula
The skeletal formula shows the functional groups without showing the rest of the chain in detail.
E.g.
2-methylpropan-1-ol bromo-1-chloropropane

11. Knowledge Check
The shortened formula of a compound is shown below. Determine their molecular, displayed and skeletal formula.
CH3CH2CH3
CH3CH2CH2OH
CH3CH(OH)CH3
CH2CCH2
CH3CCl(OH)CHCH2

12. Empirical formula
The empirical formula tells you the simplest whole number ratio of atoms in a formula.
E.g.
In Ethane, C2H6 – Is this the simplest ratio of atoms in the compound?
In 1, 4-dibromobutane, C4H8Br2 – what would the empirical formula be?

13. Empirical formula
You need to be able to work out the empirical formula of a compound given the masses or percentage masses of elements within it.
You will have done this at GCSE, but let’s have a recap anyway…

14. Empirical formula Step Action 1 find masses in grams or % 2
Element 1
Element 2 1
find masses in grams or % 2
look up Ar values of each element 3
÷ masses or % by Ar (number of moles) 4
÷ by smallest number of moles to find the simplest ratio

15. Empirical formula Example question:
A compound has the following percentage composition:
C = 12.78%
H = 2.15%
Br = 85.07%
What is its empirical formula?

16. Worked example 12.78 2.15 85.07 1 find masses in grams or % 2
Step
Action
Element 1 C
Element 2 H
Element 3 Br 1
find masses in grams or %
12.78
2.15
85.07 2
look up Ar values of each element 3
÷ masses or % by Ar (number of moles) 4
÷ by smallest number of moles to find the simplest ratio

17. Knowledge check
Have a go at the empirical formula worksheet

18. Extension Questions
The empirical formula of a compound is found to be CH2Br. Its Mr is found to be 188. What is its molecular formula?
The Mr of compound X is approximately 65. Its empirical formula is C3H8O. What is it’s molecular formula?
1,2-dibromopropane has the structural formula CH3CHBrCH2Br
What is the molecular formula for 1,2-dibromopropane
Draw the displayed formula for 1,2-dibromopropane