Homologous Series (family)
• Each series has a general formula.
• All members possess the same functional group. It is the
functional group that gives the series its characteristic
reactions.
• There is a gradual change in physical properties from one
member to the next. The most common example of this is
the increasing melting and boiling points as we go up a
series. The reason for this is that the molecules get larger
and therefore harder to break.
• Members of the same homologous series have similar
chemical properties.
Question – How many different
ways can be count up to 8?
Number of carbons in the hydrocarbon
compound;
One = Meth
Two = Eth
Three = Prop
Four = But
Five = Pent
Six = Hex
Seven = Hept
Eight = Oct
M onkeys
E at
P eanut
B utter
P andas
H ate
H airy
O ranges
(meth...
(eth…
(prop…
(but…
(pent…
(hex…
(hept…
(oct…
1 carbon)
2 carbons)
3 carbons)
4 carbons)
5 carbons)
6 carbons)
7 carbons)
8 carbons)
Alkanes
Important characteristics of the alkane
homologous series;
•The names of all alkanes end in ‘ane’
•All bonds are single (saturated)
•All alkanes follow the general formula;
Isomers and Naming
Isomers have the same chemical formula (same amount
of ‘stuff’) but a different structural formula (‘different
layout’)
For the first three members of the alkanes only one
structure is possible but butane, C4H10, has two isomers;
Rules for naming branched alkanes;
1. Find the longest carbon chain in the molecule
– the name is based on the alkane with this
number of carbon atoms.
2. Number the chain to give any branches the
lowest possible number(s).
3. Name the branches: methyl (-CH3), ethyl (C2H5), propyl (-C3H7) etc.
Worked example;
Draw and name the isomers of C5H12
Reactions of Alkanes
The alkanes are fairly unreactive however they
do burn well – therefore their main use is in
fuels;
• Combustion Example
Cycloalkanes
Characteristics
•
•
•
•
•
•
The names of all cycloalkanes start with cycloand end in –ane.
All bonds in the cycloalkanes are single.
(saturated)
Cycloalkanes are ring structures
First member of the series is cyclopropane.
Used in motor fuel, kerosene, diesel, and many
other heavy oils.
All cycloalkanes follow the general formula;
Alkenes
Important characteristics
homologous series;
of
the
alkene
• The names of all alkenes end in ‘ene’
• At least one C=C double bond (unsaturated)
• Therefore 1st member is ethene.
• All alkenes follow the general formula;
Isomers and Naming
When naming alkenes we follow the same rules
as for the alkanes with one major difference;
• the main chain (the longest chain) must
contain the double bond, whose position is
indicated by a number.
• The chain is numbered to make this number
as small as possible (the double bond takes
priority over any branches.)
Draw and name the isomers of C5H10
Saturated and Unsaturated
Hydrocarbons are described as either saturated or unsaturated.
____________ and ____________ are saturated.
They have no double (or triple) carbon to carbon bonds.
Every carbon atom is linked to neighbouring atoms by single
bonds only (C-C)
________ are unsaturated hydrocarbons.
They are unsaturated because each molecule contains at least
one carbon to carbon double bond (C=C)
Alkenes are more reactive than the alkanes and cycloalkanes
because of the carbon to carbon double bond.
Test for Unsaturation
• The test for unsaturation is a test to see if a molecule
has a double or triple bond.
• Bromine is used to test for unsaturation as it rapidly
decolourises when added to an unsaturated compound
• i.e. if bromine changes colour from orange to
colourless you have an alkene.
• This is useful for identifying an alkene and a
cycloalkane from one another if they have the same
chemical formula.
Addition Reactions
During the test for unsaturation the bromine ‘adds
on’ across the double bond, giving a saturated
compound.
This is an example of an addition reaction.
e.g.
Propene +
Bromine
dibromopropane
Another Example;
Pentene
+
Bromine = bromo…
Chlorine = chloro…
Fluorine = fluoro…
Iodine = iodo…
Nitrogen = nitro…
Bromine
dibromo_________
Another Example;
Heptene
+
Hydrogen
_________
Butene
+
Oxygen
Ethene
+
Water
Alcohols
• The names of all alcohols end in ‘-ol’
• The functional group of the alcohols is –OH (hydroxyl group)
• Alcohols are substituted alkanes (as an -H has been replaced
with an –OH)
• Alcohols are made via hydration of alkenes and fermentation.
• Alcohols make useful industrial solvents.
• All alcohols follow the general formula;
Isomers and Naming
Isomers can result from both branching and varying
the position of the -OH group.
In naming, the main chain (longest chain) must contain
the -OH group, whose position is indicated by a
number.
Example;
Pentan-1-ol, Pentan-2-ol, Pentan-3-ol
Example 2 – Draw the 4 isomers of C4H9OH
Alcohols as Fuels
Alcohols make really good fuels and burn with
a clean flame.
A reaction (like combustion) which gives out
heat to the surroundings is classed as
exothermic.
The opposite of an exothermic reaction is an
endothermic reaction (i.e. heat is taken in.)
Carboxylic Acids
• The names of all carboxylic acids end in ‘-oic acid’
• The functional group of the carboxylic acids is -COOH
(carboxyl group)
• This carboxyl group is always attached to the end
carbon.
• Carboxylic acids react like other acids
• General Formula;
Vinegar
• Vinegar is dilute ethanoic
acid.
• Vinegar has been used
for years in cooking both
as a flavouring and as a
preservative.
• Vinegar is also a useful
cleaning agent and is
found in many household
products.
Making Esters
Esters are compounds formed by a condensation
reaction between alcohols and carboxylic acids.
In a condensation reaction two molecules join and a
small molecule (often water) is removed.
Esters are used as flavourings in food and perfumes
as well as industrial solvents.
Naming Esters
The name of an ester indicates the alcohol and
acid which go into making it.
• The first part is from the alcohol: eg.
-anol becomes -yl. (i.e. ethanol becomes ethyl)
• The second part is from the carboxylic acid: e.g.
-oic becomes -oate. (i.e. ethanoic becomes ethanoate)
Fuels Calculation
We can calculate the energy released by a fuel
using the following equation;
Eh = c x m x ΔT
where:
c=
m =
ΔT =
Eh =
Specific heat of water, 4.18 kJ kg−1 °C−1 (data book)
Mass of water in kg
Temperature change of water in °C
Energy (kJ)
Worked Example 1
Calculate the amount of energy produced when 0.5g
of methanol is burned to heat 250cm3 of water.
The water temperature went up by 2°C.
Worked Example 2
Calculate the amount of energy produced when 200g
of methane is burned to heat 50cm3 of water. The
initial temperature of water was 25°C and at the end
of the experiment the temperature was found to be
65°C.
Worked Example 3
Calculate the amount of energy produced from the
following results;
Methanol mass before
Methanol mass after
Mass of water heated
Temp rise in water
53.65g
53.46g
100g
10°C