module 4 Flashcards
properties of alkanes
-general formula - CnH2n+2
-non-polar as theres no significant difference between the electronegativities of carbon and hydrogen
-used as fuels
structure and bonding of alkanes
-there are 4 bonding pairs and 0 lone pairs around the C atom
-tetrahedral shape and 109.5
-all electron pairs repel
sigma bonds
-caused by end on end overlap of bonding orbitals directly between atoms
-how well they overlap determines bond strength
alkanes boiling and melting points - chain length
-as the chain length increases
-the boiling and melting points increase
-longer chains have more points of surface contact between molecules
-increases the strength of induced dipole dipole interactions between molecules
-more energy need to overcome
alkanes boiling and melting points - isomers
-the more branches in an isomer molecules the lower the boiling point
-there are less points of surface contact between molecules
-so weaker induced dipole dipole interactions between molecules
-less energy needed to overcome
complete combustion
burning of a substance in excess supply of oxygen
incomplete combustion
-burning of a substance in a limited supply of oxygen
radical
highly reactive species with an unpaired electron
homolytic fission
covalent bond breaks and one electron goes to each atom forming two radicals
heterolytic fission
covalent bond breaks and both electrons goes to one atom forming two ions
pi bonds
sideways overlap of p orbitals to give a pi bond above and below
nucleophiles
electron par donator
-regions of high electron density
testing for alcohols
-tertiary alcohols don’t react with acidified potassium dichromate
-add a few drops of potassium dichromate and conc. sulphuric acid
-colour change from orange to green shows the presence of 1 and 2 alcohols
testing for alkenes
-add bromine water and shake
-colour change from orange to colourless shows the presence of a double bond
properties of alcohols
-polar molecules
-due to the elctronegativite hydroxyl groups which pulls the electrons in the C-OH bond away from the carbon atom
boiling points of alcohols
-alcohols have higher boiling points than alkanes
-alcohols are less volatile than alkanes of similar carbon atoms
solubility of alcohol - short chain lengths
-soluble in water
-alcohol and water molecules make hydrogen bonds with each other
-alcohols make neutral solutions
-the more OH groups the more hydrogen bonds so the alcohol is more soluble
solubility of alcohol - long chain lengths
-the greater the chain length the less soluble the alcohol is in water
-there are stronger induced dipole dipole interactions
-which break up hydrogen bonds between molecules
properties of alkanes
-formula CnH2n
-unsaturated hydrocarbon with at least one C=C bond
-alkenes are more reactive than alkanes in addition reactions
shape and rotation - alkenes
-triganol planar around each atom in the C=C bond
-no rotation around the C=C bond as p orbitals must stay in their position to overlap and form pi bond
-C-C bonds still rotate
define stereoisomers
-the same structural formula but different arrangement of atoms in space
disposing of waste - polymers
-polymers are unreactive so arent biodegradable
-pro: long lasting and reusable
-con: difficult to dispose of
uses of mass spectrometry
-determine the abundance of isotopes in an element
-monitor breathing of patients under anastethic
-testing for drug use
-analysing molecules in space
-testing for toxic chemicals in marine life
describe purification through a seperating funnel
-products of a reaction and water is added to the separating funnel, shaken then allowed to settle
-the less dense organic layer settles at the top
-water soluble impurities dissolve in the lower aqueous layer
-open tap using stopper so aqueous layer is run off
