P1- The Homologous Series Flashcards
Hydrocarbon
Substance containing only hydrogen and carbon
3 families: alkanes, alkenes, cycloalkanes
Alkanes
Always end in ane
Prefix indicating number or carbons
Saturated- only single bonds
Flammable so make fuels
Insoluble
Readily undergo combustion reactions in the prescence of oxygen
E.g methane- fuel to make heat and light
propane- home and water heating
octane- proper functioning in modern engines
Drawing hydrocarbons
Carbon group 4- valency 4- 4 bonds
Hydrogen- group 1- valency 1- 1 bond
Molecular formula- number of each element
Full structural formula- atoms and all bonds
Shortened structural formula- how hydrogen atoms arranged around carbon without showing bonds
First 8 alkanes
Number of Molecular Full Shortened
Hydrocarbon Carbons Formula Formula Formula
H
| Methane 1 CH4 H - C - H CH4
|
H
H H
| | Ethane 2 C2H6 H - C - C - H CH3CH3
| |
H H
H H H
| | | Propane 3 C3H8 H - C - C - C - H CH3CH2CH3
| | |
H H H
Butane 4 C4H10 CH3CH2CH2CH3
Pentane 5 C5H12 CH3CH2CH2CH2CH3
Hexane 6 C6H14 CH3CH2CH2CH2CH2CH3
Heptane 7 C7H16 CH3CH2CH2CH2CH2CH2CH3
Octane 8 C8H18 CH3CH2CH2CH2CH2CH2CH2CH3
Homologous series
Family of compounds with the same general formula, similar chemical properties and gradually changing physical properties
Where do alkanes come from
From natural gas or from fractional distillation of crude oil
General formula of alkanes
CnH2n+2
2 x number of carbons + 2
Melting and boiling points of hydrocarbons
Increase because as the molecular size increases, the strength of the intermolecular forces increases so more heat energy is required to separate large molecules
Cycloalkanes
Start with cyclo and end in ane
Contain a ring of carbons
Saturated because contain carbon to carbon single bonds
Cycloalkanes general formula
CnH2n
First 8 members of cycloalkanes
Name Number of carbon atoms Molecular formula
Cyclopropane 3 C3H6 Cyclobutane 4 C4H8 Cyclo-pentane 5 C5H10 Cyclohexane 6 C6H12 Cyclo-heptane 7 C7H14
Cyclo-octane 8 C8H16
Alkenes
End in ene
Prefix indicating number of carbon atoms
Contain at least one carbon to carbon double bond making it unsaturated and reactive
Insoluble
Alkenes general formula
CnH2n
Alkenes uses
Making polymers (plastics)
Industrial production of ethanol
Fuels
Solvents
First 7 members of the alkenes
Name Carbons Molecular Full Short
H H
| | Ethene 2 C2H4 C=C CH2=CH2
| |
H H
H H
| | Propene 3 C3H6 C=C-C-H CH2=CHCH3
| | |
H H H
H H H
| | | Butene 4 C4H8 C=C-C-C-H CH2=CH2CHCH3
| | | |
H H H H
H H H H
| | | | Pentene 5 C5H10 C=C-C-C-C-H CH2=CH2CHCH2CH3
| | | | |
H H H H H
H H H H H
| | | | | Hexene 6 C6H12 C=C-C-C-C-C-H CH2=CH2CHCH2CH2CH3
| | | | | |
H H H H H H
H H H H H H
| | | | | | Heptene 7 C714 C=C-C-C-C-C-C-H CH2=CH2CHCH2CH2CH2CH3
| | | | | | |
H H H H H H H
H H H H H H H
| | | | | | | Octene 8 C8H16 C=C-C-C-C-C-C-C-H CH2=CH2CHCH2CH2CH2CH2CH3
| | | | | | | |
H H H H H H H H
Branched chain alkanes
Carbon atoms attached to side of main chain
End in yl
Prefix indicating number of carbons
First 4 branch names
Methyl
Ethyl
Propyl
Butyl
Naming branched chain alkanes
Count from side closest to branch
Position of branch(es) - prefix for number of branches name of branch name of chain
Naming branched chain alkenes
Count from side closest to double bond
Position of branch - prefix for no. branches name of branch alkene prefix - double bond position - ene
Isomer
Molecules with the same molecular formula but different structural formula
They usually have different physical properties
Reactions that hydrocarbons take place in
Combustion
Addition reactions of alkenes
Cracking
Combustion
Burning
Forms carbon dioxide and water in a plentiful supply of oxygen
Forms carbon monoxide and water in a limited supply of oxygen
Hydrocarbon + oxygen —> carbon dioxide + water
Addition reactions of alkenes
Halogenation
Hydrogenation
Hydration
The carbon to carbon double bond breaks and other reactants add across the double bond
Halogenation
Testing for unsaturation by testing the effect hydrocarbons have on bromine solution
Halogens form dihaloalkanes
Alkene + bromine —> dibromoalkane
Bromine - Br-Br
Hydrocarbon effect on bromine solution
Alkanes and cycloalkanes are saturated so the bromine solution stays the same because no more atoms can be added to the molecule because each carbon is already bonded to 4 other atoms
Alkenes are unsaturated so bromine water is decoloroised
Hydrogenation
Hydrogen forms alkanes
Alkene + hydrogen —> alkane
Hydrogen H-H
Hydration
Water forms alcohols
Alkene + water —> alcohol
Alcohol- H-OH
Cracking
A process in which long chain hydrocarbon molecules are broken down into shorter, more useful molecules using heat and a catalyst
Catalyst allows reaction to be done at a lower temperature
Delivery tube should be removed before heating is stopped
Produces a mixture of alkanes and alkenes because the long chain hydrocarbon molecule can break at different points
Equation should have same number of carbon and hydrogen atoms on products and reactants sides
What is cracking used for
To convert the larger, less valuable fractions of crude oil into petrol
