Alkanes Flashcards
Give 3 reasons why carbon can form so many compounds?
Can form 4 covalent bonds to other atoms
Can form single, double or triple bonds
Can bond to other Carbon atoms to form long chains
Definition of a hydrocarbon?
Compound containing Carbon and Hydrogen only
What does alicyclic mean?
Organic compounds which combine cyclic structures with aliphatic properties
What does aliphatic mean?
Organic compounds which carbon atoms form open chains, not aromatic rings
What does aromatic mean?
Organic compound containing a planar unsaturated ring of atoms which is stabilised by an interaction of the bonds forming the ring
What does saturated mean?
Contains greatest number possible number of hydrogen atoms, without c-c double or triple bonds
What does unsaturated mean?
Organic molecule which has c-c, double or triple bonds, so doesn’t have the greatest amount of hydrogens
What is a homologous series?
A series of organic compounds having the same functional group, but with each successive member differing by CH2
What is a functional group?
A group of atoms responsible for the characteristic reactions of a compound
Alkane with 1 carbon?
Methane CH4
Alkane with 2 carbons?
Ethane C2H6
Alkane with 3 carbons?
Propane C3H8
Alkane with 4 Carbons?
Butane C4H10
Alkane with 5 Carbons?
Pentane C5H12
Alkane with 6 carbons?
C6H14
Alkane with 7 Carbons?
Heptane C7H16
Alkane with 8 carbons?
Octane C8H18
Alkane with 9 carbons?
Nonane C9H20
Alkane woth 10 carbons?
Decane C10H22
What’s the general formula for alkanes?
CnH2n+2
General formula for cycloalkanes?
CnH2n, carbons form ring structure
What’s the empirical formula?
The simplest whole number ratio of atoms of each element present in a compound
What’s the molecular formula?
The actual number of atoms of each element in a molecule
What’s the general formula?
The simplest algebraic formula of a member of a homologous series
What’s the structural formula?
Minimal detail that shows the arrangement of atoms in a molecule- eg brackets show branching, use C’s as a starting point
What’s the displayed formula?
The relative positioning of all the atoms in a molecule, including the bonds between them, ie drawn out with all bonds shown
Skeletal formula?
Use zig zag lines for carbon chain, each intersection/end = a carbon, no hydrogens shown, for functional groups have extra line drawn to them
How to name an organic compound?
Identify the longest carbon chain, make this the stem eg. Hex for 6C
See if it’s saturated or unsaturated (ane or ene), or is a different type eg. alcohol, and put this behind stem (if ene, put number(s) inbetween stem and ene to show where double/triple bonds are
Identify any alkyl chains (methyl, ethyl, propyl etc), and put this in front of stem then in front of that if there is more than 1, put “di, tri etc” then in front of that put the Carbon numbers where they occur.
Apply the same rule to functional groups, except they go infront of alkyl chains, and have smallest numbering priority.
What’s the suffix when the functional group is OH? (alcohol)
ol
What’s the suffix when the functional group is ?Carbon is double bonded to Oxygen and a hydrogen and another hydrogen or a C chain? (Aldehyde)
al
What’s the suffix when the functional group is Carbon is double bonded to oxygen, and bonded to 2 C chains? (ketone)
one
What’s the suffix when the functional group is Carbon double bonded to Oxygen an OH group, and either H or a C chain? (Carboxylic acid)
Oic acid
What are structural isomers?
Compounds with the same molecular formula but different structural formulae
3 ways structural isomers can occur?
Chain isomers- hydrocarbon chain may be branched or unbranched
Position isomers- hydrocarbon chain stays the same, but functional group found in different positions
Functional group isomers- When the functional group is different
What must an Alkane be?
Homologous series, saturated and a hydrocarbon
Why are Carbon atoms not arranged in a straight line?
Each Carbon in an alkane has four bonding pairs, and zero lone pairs, therefore all the bond angles will be 109.5 degrees
In alkanes why does when the amount of Carbons increase so does the boiling point?
Because the strength of the London forces between molecules increases
With more atoms there are more electrons, so the strength of the London forces increases
If there are stronger forces attracting the molecules together, more energy is required to separate the molecules
What happens to the boiling point in alkanes when branching is increased?
The boiling point decreases
There is smaller contact area between molecules, meaning the London forces are weaker, so less energy required to break intermolecular forces
Why are alkanes unreactive?
They only contain C-C bonds and C-H bonds, which are strong and hard to break.
C-C bonds are non polar and the electronegativities of C and H are similar enough that the C-H bond is considered non polar. The lack of polar bonds makes it difficult for alkanes to attract an attacking species
What’s complete combustion?
When there is a plentiful supply of Oxygen, and alkanes burn cleanly producing a blue flame.
All carbon atoms are oxidised to Carbon Dioxide, and all the hydrogen to water
General formula for complete combustion of an Alkane?
CxHy + (x+1/4y) O2 = x CO2 + 1/2y H2O
What’s the incomplete combustion of alkanes?
When the supply of Oxygen is limited, yellow flame seen. The carbon may form carbon monoxide, or just carbon as soot. All hydrogen atoms still oxidise to water
Why can incomplete combustion be dangerous?
Carbon monoxide is toxic, and causes death by preventing haemoglobin from carrying oxygen to respiring tissues.
CO is colourless and odourless so presence is difficult to detect
Equation for methane reacting with a halogen eg chlorine?
CH4+Cl2 = CH3Cl + HCl
What conditions are required for methane reacting with a halogen eg chlorine?
UV light
What type of reaction is methane reacting with a halogen eg chlorine?
Substitution, one of the H’s in CH4 has been replaced by a Cl
What is a reaction mechanism?
Looks at what’s happening during a chemical reaction in terms of the movement of electrons
What type of mechanism happens when an alkane and a halogen react?
Radical substation?
What is a radical?
A species with an unpaired electron
What’s the chemical notation for a radical?
a dot •, eg the chlorine radical Cl•
What are the 3 steps in a radical substitution mechanism?
Initiation, propagation, termination
Equation what happens in the initiation stage?
Br2= 2 Br•
What type of bond fission produces radicals?
Homlytic, “even splitting”, because the covalent bond between the halogen has a shared pair of electrons, when it splits each halogen receives one electron, meaning each will have an unpaired electron
Why is UV light required in the initiation stage?
To provide activation energy by breaking the halogen bond homlytically
What are the 2 equations in the propagation stage in the reaction of Methane and Bromine?
Br• + CH4 → HBr + CH3•
CH3• + Br2 → CH3Br + Br•
In terms of radicals what is the key feature of the propagation step?
For every radical used in the reaction, a new radical is produced
What are the 3 equations in the termination stage?
CH3• + Br• → CH3Br
Br• + Br• → Br2
CH3• + CH3• → CH3CH3
In terms of radicals what is the key feature of the termination step?
2 radicals combine to form a product which isn’t a radical
