alkanes Flashcards
what are sigma bonds
covalent bonds in organic compounds, formed from a direct overlap of orbitals, one from each bonding atom eg C-C or C-H
Name the process used to obtain kerosene from crude oil and explain how it works
Fractional distillation. different fractions in crude oil have different boiling points so each fraction vaporises separately from the other fractions and can be collected.
why do straight chains have a higher boiling point than branched chains
There is more surface contact between straight chain isomers so more London forces have formed between the chains therefore more energies required to break them
Why does boiling point increase up the alkane homologous series
As chain length increases there are more points of contact between molecules where London forces can form so more energy is required to break them
Describe the bonding in Ethane, State and explain the sigma bond angles in a molecule
Single covalent Sigma bonds (The overlap of orbitals one from each bonding atom), each carbon atom is bonded to 4 other atoms by these bonds.
the shape around each carbon atom is tetrahedral.
the 4 bonding pairs of electrons repel equally to give a bond angle of 109.5
what are alkanes and their uses
Saturated hydrocarbons, Are the main components of crude oil and natural gases which are used as fuel
What is the general formula of alkanes
CnH2n+2
Why are alkanes not very reactive
Sigma covalent bonds are very strong and C - C are non polar and C-H has little difference in electronegativity so little very polarity
what are the states of the first 10 alkane
First 4 are gas
Next 4 are liquid
Last 2 are solid
What is the reaction between exess oxygen and alkenes and what does it produce
its a Combustion reaction producing carbon dioxide and water And releasing heat
why are alkanes used as fuel
They are readily available, easy to transport And combust with oxygen without releasing toxic products
what happens when alkanes react with a limited supply of oxygen And what is produced
Incomplete combustion occurs producing water and carbon monoxide or just carbon as soot
Why is incomplete combustion dangerous
because carbon monoxide: a colourless, odourless, highly toxic gas is produced, It combines with haemoglobin to stop transporting oxygen around the body
When does incomplete combustion usually occur
When attempted in a closed space
like car engines, faulty heating systems, inadequate ventilation in living areas
What does radical substitution need to take place
UV light from sunlight
What happens in initiation
where the covalent bond in bromine is broken by homolytic fission forming two highly reactive bromine radicals Br2 -> UV Br. + .Br
What happens in propagation step one
bromine radical reacts with a methane forming a methyl radical and hydrogen bromide CH4 + Br. -> .CH3 + HBr
What happens in propagation step 2
Methyl radical reacts with a new bromine forming bromomethane and a new bromine radical .CH3 + Br2 -> CH3Br + Br.
What happens in termination
Two radicals collide
Br. + .Br -> Br2
.CH3 + .CH3 -> C2H6
.CH3 + .Br -> CH3Br
What are the limitations in radical substitution and why
Further substitution: Another bromine radical can collide with the bromomethane made, substituting a further hydrogen and so on resulting in a mixture of: CH3Br CH2Br2 CHBr3 CBr4
Substitution at different positions: With the chain length bigger than ethane there could be different structural isomers formed depending on the position of the bromine radical. And with Addition of further substitution, more possibilities occur, even for ethane.
What is radical substitution used to for
To make Haloalkanes
what is the molecular formula of an Organic compound formed by substitution of all the H atoms in butane by Cl atoms
C4H10 + 10 Cl2 → C4Cl10 + 10 HCl
what are structural isomers
molecules with Different structural formulae and same molecular formula
