DF3 - Hydrocarbons Flashcards
What is fractional distillation?
When crude oil is heated to vaporise it + the vapour passes into a distillation column
What is a homologous series?
A group of compounds that have a similar structure/ the same general formula
Give an example of a homologous series
Alkanes
What is catenation?
The bonding of atoms of the same element into a chain/ring. Carbon can form strong covalent bonds with itself to give chains/rings
How many bonds can carbon form?
4 covalent bonds
What are hydrocarbons?
Compounds containing only carbon and hydrogen
Name 4 types of hydrocarbon
Alkanes, alkenes, arenes + cycloalkanes
What is the general formula for alkanes?
C n H 2n+2
What is the general formula for alkenes?
C n H 2n
What is the general formula for arenes?
C n H n
What is the general formula for cycloalkanes?
C n H 2n
What are aromatic compounds?
Compounds that contain one or more benzene rings
What are aliphatic compounds?
Compounds that do not contain any benzene rings
Which 2 types of hydrocarbons are more unreactive out of the 4?
Alkanes + arenes
What are functional groups?
Modifiers that are responsible for the characteristic chemical reactions of molecules (but when added to a hydrocarbon framework it can change its properties)
Which one is more reactive, a c-c or c=c bond?
A c=c double bond (in alkenes)
Are alkanes saturated or unsaturated?
Saturated
What does it mean if alkanes are saturated?
They contain the maximum number of hydrogen atoms possible (no double/triple bonds)
Name the first 10 alkanes
Methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane + decane
Are the chemical properties the same for all of the compounds in a homologous series?
They all have similar chemical properties
Are the physical properties the same for all of the compounds in a homologous series?
Physical properties e.g boiling/melting point + density change gradually as no. of C atoms increase
Describe molecular formula
Shows the no. of each type of atom present. Does not tell us anything about bonding within compound
Describe empirical formula
Simplest ratio of the elements present in a molecule. Does not tell us anything about bonding within compound
Describe condensed formula
Each carbon in the molecule is written out in turn, with the atoms attached to it written directly after. Brackets are used to indicate branching in the molecule, or multiple identical groups
Describe displayed formula
Represents the molecule by showing all of the atoms, and all of the bonds between those atoms. Bonds are represented by lines, with the number of lines representing the strength of the bond (e.g 1 line is single bond and 2 lines is double bond)
Describe structural/shortened structural formula
It is similar to display formula but not all bonds are shown. All atoms are still indicated using subscript numbers. Carbon hydrogen bonds are often simplified.
Describe skeletal formula
The main carbon chain is represented as a zig-zagging line, where the end of lines and the vertices represent carbon atoms. Functional groups + atoms other than carbon/hydrogen are always shown
What are two types of alkane chains?
straight chains and branched chains
What are structural isomers?
When two compounds have the same molecular formula but different structural formulas
Give a structural isomer of butane
Methylpropane
Name at least 3 of the 5 common alkyl groups
Methyl: CH3 - Ethyl: CH3CH2 - Propyl: CH3CH2CH2 - Butyl: CH3CH2CH2CH2 - Pentyl: CH3CH2CH2CH2CH2 -
What letter often represents side groups?
R
How can you determine the systematic name of a hydrocarbon?
By using the full structural formula
Systematic name is derived from a set of rules
What are the rules/steps to giving a systematic name to alkanes?
- Name the longest chain
- Identify any side chains off the main chain and name them
- State the location of any side chains by prefixing the name of the side chain with the number of the carbon atom to which the side chain is attached
- Keep the number as low as possible
- If there is more than one side chain, rules still apply. When naming, state the side chain in alphabetical order. Use prefixes ‘di’ or ‘tri’ depending on how many of the same side chain you have
- Name the compound by starting with the side chains + their location first, then the ‘parent’ chain. Use hyphens between numbers + letters + commas between numbers
How do you name cycloalkanes?
- Count the number of carbons in the cyclic structure + identify appropriate prefix to name the alkane
- Add alkane name to the enf of ‘cyclo’
- If there are side chains same rules from alkanes apply
The state of an alkane at room temp. is dependent on the number of carbon atoms (size of molecule). How many carbons are in solid, liquid and gas alkanes.
Colourless gases: n = 1-4
Colourless liquids: n = 5-16
White waxy solids: n = 17+
Alkanes mix well with each other. Why don’t they mix well with water?
- Alkanes + water form two separate layers
- Alkanes contain non-polar molecules but liquids such as water contain polar molecules that attract each other + prevent alkane molecules from mixing with them
Describe the structure of arenes
They have c-c and c=c bonds one after the other in a ring shape (in skeletal formula they are same as cycloalkanes apart from the fact they have a circle in the middle - delocalised electrons in there)
