C HEMISTRY AS R EVISION Chains, Energy and Resources: Module 1

K EY W ORDS Hydrocarbons; organic compounds that contain carbon and hydrogen only Saturated Hydrocarbon; hydrocarbon with single bonds only Unsaturated Hydrocarbon; hydrocarbon containing carbon to carbon multiple bonds Aliphatic Hydrocarbon; hydrocarbon with carbon atoms joined together in straight or branched chains Alicyclic Hydrocarbon; hydrocarbon with carbon atoms joined together in a ring structure Functional Group; the part of the organic molecule responsible for its chemical reactions Homologous Series; series of organic compounds with the same functional group but with each successive member differing by CH 2 Alkanes; homologous series with the general formula C n H 2n+2 Alkyl Group; an alkane with a hydrogen atom removed. Stereoisomers; compounds with the same structural formula, but with a different arrangement of the atoms in space

K EY W ORDS E/Z Isomerism; stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond Radical; species with an unpaired electron. Nucleophile; an atom (or group of atoms) that is attracted to an electron rich centre or atom, where it donates a pair of electrons to form a new covalent bond. Electrophile; an atom 9or group of atoms) that is attracted to an electron rich centre or atom, where it accepts a pair of electrons to form a new covalent bond. Cracking; breaking down of long chained saturated hydrocarbons to form a mixture of shorter chains alkanes and alkenes Catalyst; substance that increases the rate of a chemical reaction without being used up in the process. Π Bond; reactive part of a double bond formed above and below the plane of the bonded atoms by a sideways overlap of p-orbitals. Curly Arrows; symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond Polymer; long molecular chain built up from monomer units Monomer; small molecule that Comines with many other monomers to form a polymer Biodegradable Material; Material that is broken down naturally in the environment by living organisms

T YPES OF O RGANIC R EACTION Addition Reaction; reactant is added to an unsaturated molecules to make a saturated molecule 2 reactants  1 product Substitution Reaction; an atom or group of atoms is replaced with a different atom or group of atoms 2 reactants  2 products Elimination Reaction; removal of a molecules from a saturated molecules to make an unsaturated molecule 1 reactant  2 products

T YPES OF C HEMICAL F ORMULAE General Formula; simplest algebraic formula for a member of a homologous series. Displayed Formula; shows the relative positioning of all the atoms in a molecule, and the bonds between them. Structural Formula; minimal detail for the arrangement of atoms in a molecule. Skeletal Formula; simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.

F IRST T EN M EMBERS OF A LKANE H OMOLOGOUS S ERIES Number of carbon atoms in longest chainName 1Meth ane 2Eth ane 3Prop ane 4But ane 5Pent ane 6Hex ane 7Hept ane 8Oct ane 9Non ane 10Dec ane

T YPES OF I SOMERS Structural Isomer; same molecular formula but with different structural formulae. (Different order) Stereoisomer; same structural formula but with a different arrangement in space. (Same order, different places)

T IPS F OR W ORKING O UT I SOMERS Shorten the chain Move functional groups along chains If double bond present, move things around it. Chiral centre; has four different groups attached to one carbon atom, means the mirror images are non super imposable.

T YPES OF C OVALENT F ISSION Homolytic Fission; breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals Heterolytic Fission; breaking of a covalent bond with both of the bonded electrons going to one of the atoms forming a cation (+ ion) and an anion (- ion).

P ERCENTAGE Y IELDS AND A TOM E CONOMY

F RACTIONAL D ISTILLATION Takes place in a fractional column, decreases in temperature from 400°C at the bottom to 20°C at the top. 1. Crude oil vaporised by heating, passed into column 2. Gases pass through the different levels of the column until they reach a temperature that is lower than their boiling point 3. Vapour condenses to liquid, which are tapped off. Short chain hydrocarbons (lower BPs) condense near the top, longer ones near the bottom.

V AN DER W AALS ’ F ORCES AND B OILING P OINTS As chain length increases, the boiling point increases because the Van der Waals’ between molecules become stronger. More energy required to break the increasing number of Van der Waals’ forces. A branched isomer has a lower BP than an unbranched one. Fewer points of contact between molecules, so fewer Van der Waals’. Cannot get as close together, decreasing the Van der Waals’

C OMBUSTION AND I NCOMPLETE C OMBUSTION OF A LKANES Complete Combustion; Occurs in plentiful supply of oxygen. CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O (l) Incomplete Combustion; Occurs in limited supply of oxygen. C 8 H 18 (l) + 8 1/2 O 2 (g)  8CO (g) + 9H 2 O (l) CO is colourless and odourless. CO is poisonous, prevents haemoglobin binding with oxygen

C ATALYTIC C RACKING Short chain hydrocarbons used as fuels and for polymer production Cracking; breaking down long chained saturated hydrocarbons to form a mixture of short chained alkanes and alkenes

I SOMERATION Unbranched alkanes converted into branched alkanes into branched alkanes. Promotes more efficient combustion

R EFORMING Unbranched hydrocarbons converted into cyclic hydrocarbons. H 2 (g) is always produced as a result. Promotes more efficient combustion

C ONTRASTING T HE V ALUE OF F UELS FOR E NERGY WITH O VER R ELIANCE AND P LANT B ASED F UELS. I NCREASED CO2, G LOBAL W ARMING, C LIMATE C HANGE Rely on it for electrical generation and transport Feedstock Reducing reserves of oil has pushed the price up, scientists looking for alternatives Environmental impact, scientists looking for alternatives Leads to release of atmospheric pollutants: carbon monoxide, carbon dioxide, nitrogen oxides and sulphur dioxide Green house gases lead to global warming leading to change in climates. Bio fuels are alternatives.

F REE R ADICAL S UBSTITUTION Halogenation of Alkanes 1. Initiation 1. Cl-Cl bond in chlorine molecule is broken by homolytic fission, forming two chlorine radicals. UV provides the energy for this bond fission 2. Cl-Cl  2Cl 2. Propagation 1. Methane reacts with chlorine radical. Single C-H bond is broken by homolytic fission, forming a methyl radical CH 3. HCL also formed 1. CH 4 + Cl  CH 3 + HCl 2. Methyl radical reacts with chlorine molecule, creating chloromethane and a further chlorine radical. 1. CH 3 + Cl 2  CH 3 Cl + Cl 3. Termination 1. Two radicals combine to form a molecule. Number of possible termination steps, because of the large numbers of radicals. 1. Cl + Cl  Cl 2 2. CH 3 + CH 3  C2H 5 3. CH 3 + Cl  CH 3 Cl

A DDITION REACTIONS OF A LKENES Addition of Hydrogen (Hydrogenation) H (g) and alkene (g) passed over nickel catalyst at 150°C Alkane is formed, double bond broken Hydrolysis Addition of to an alkene to make an alcohol

E LECTROPHILIC A DDITION Formation of dihalogenoalkanes. Can be tested for using bromine water (Orange to colourless) Halogenation

A DDITION P OLYMERISATION OF A LKENES

P ROCESSING OF W ASTE P OLYMERS Separated into types and then recycled Combustion for energy Use as a feedstock for cracking in the production of plastics and other chemicals

R OLE OF C HEMISTS IN M INIMISING E NVIRONMENTAL D AMAGE Removal of toxic waste products Removal of HCl formed during the disposal by combustion of halogenated plastics (PVC) Development of biodegradable and compostable polymers.