Chapter 8.1 Alkanes Flashcards
(24 cards)
Carbon forms more compounds than all other elements combined because of its properties?
What are they?
- has 4 VALENCE ELECTRONS so it has the potential to from covalent bonds with four different atoms
- Carbon atoms can form strong covalent bonds with other carbon atoms.
- The covalent bonds formed can be a combination of single, double or triple bonds.
Example of Carbon based compounds
- Caffeine
- petrol
- pesticides
- plastics
- artificial flavours
What is crude oil?
Fossil fuel - low in density (
*making able to migrate upwards through the crust where it often became trapped beneath impervious (unable to pass through) rock. Accumulation of oil and gas under the rock creates an oil felid.
Over millions of years dead Organic material was affected by high pressures and temperature (buried under the earths’s crust via sediment),causing the oil and fats to be converted into hydrocarbon.
How is crude oil used?
Not used in raw state
Transported from oil fields to oil refineries where it undergoes fractional distillation in a fraction given tower.
In this process crude oil is separated into its various components or fractions.
Each fraction is made up of a range of hydrocarbons with similar boiling points and hence molecular masses.
The compounds of crude oil that are obtained by fractional distillation are used for a wide range of purposes but now 90% is used for fuels.
Further processing of crude oil fractions is needed to these components even more useful.
Heavier fractions undergo a process called CRACKING,
This process breaks the larger hydrocarbon molecules into smaller molecules using HEAT and a catalyst.
The smaller molecules and especially those with carbon-carbon double bonds (called alkenes) are needed by the petrochemical industry.
What is a hydrocarbon? Which is the simplest one?
Hydrocarbons are an organic compound composed of only carbon and hydrogen.
Simplest form is Methane - CH4; one carbon atoms is covalent bonded to 4 hydrogen atoms to form a molecule.
What does saturated mean?
Containing the greatest possible number of hydrogen atoms, without carbon-carbon double/triple bonds
What is a homologous series?
A series of molecules in which each member differs by -CH2- from the previous members
Eg, each member of the alkenes series differs from the previous member by a -CH2 - unit.
What are the characteristics of compounds that are members of the same homologous series?
- similar structure
- a pattern to their physical properties
- similar chemical properties
- the same general formula
What is an Alkane?
Alkanes are hydrocarbons that contain only single bonds.
- all Carbon-Carbon bonds are single covalent bonds
Alkane chemical formula?
CnC2n+2
What are the properties of an Alkane?
- Saturated
- Naming ends with -and
- Formula - CnH2n+2
- Non polar
Why are Alkanes non- polar?
Alkanes only have weak forces between molecules because they are non-polar.
As the number of carbons and the size of the molecules increase within its homologous series, the strength of the these forces increases so the melting and boiling points of alkanes increases
What happens as homologous series increases in size?
- Bonds around each carbon atom adopts a tetrahedral shape
- boiling and melting points increase
List Stem/ parent names in order (conventions of naming a hydrocarbon)
- Meth-
- Eth-
- Prop-
- But-
- Pent-
- Hex-
- Hept-
- Oct-
- Non-
- Dec-
Why are alkanes saturated?
Carbon atoms are bonded to as many atoms as they can, therefore no other atoms can be added cannot be added to them.
- have no double bonds only carbon-carbon single bonds and so alkanes are combined with the maximum number of atoms.
Since alkanes are saturated
They do not react with and decolourise bromine water.
Eg hexane will not react with bromine water because all bonds are effectively occupied with either a H or C
For the same reason alkanes cannot be converted into polymers like poly (ethene) made from ethene.
Structural formula
Diagram which Shows all the bonds in a molecule, but lone pairs can be omitted
Condensed structural formulae
Aka semi-structural formulae
Shows the atoms that are connected to each carbon atom but do not shows the bond
What are structural isomers?
Molecules that have the same molecular formula but different arrangement in atoms are said to be structural isomers of each other.
The more atoms in a molecule the more possible isomers there are.
Are compounds with different physical and chemical properties
Eg boiling and melting points are different because the forces of attractions between the different versions of hydrocarbon molecules are affected by the structure of the different molecules.
What are alkyl groups?
Alkyl groups have one less hydrogen atom than the corresponding alkane of the same name
General formula is -CnH2n+1
When writing the condensed structural formula of a branched alkane, alkyl groups are written with brackets
What is the IUPAC?
International union of pure and applied chemist
Under this system the name of the hydrocarbon provides the detail of its structure
Rules to use when naming the hydrocarbon
- Longest chain of carbons = stem name
- Number carbon atoms so that branching smaller groups are given the smallest number
- Identify type and number of the alkyl groups attached to the chain
- Place number position of the alkyl group in-front of compounds Name
- If two identical side chains are present use di or tri prefix
- List alkyl side chains in alphabetical order with numbers to indicate respective positions
List the alkyl groups (side groups)
Methyl Ethyl Propyl Butyl Pentyl Hexyl Heptyl Octyl
