2Why is carbon important? Carbon makes up over 90% of all chemical compoundsThey form the basis of living systemsCarbohydrates all have carbonProteins contain carbonFats contain carbon
3How does carbon form so many compounds? Carbon has 4 valence electrons, all available for bonding with other atomsCarbon can form strong covalent bonds with other carbon atomsBonds between carbons can be single or multiple
4HydrocarbonsHydrocarbons are made up of different compounds of hydrogen and carbon.There are many different hydrocarbonsThey make up the majority of the petroleum and natural gas industryHydrocarbons can be classified into several families or homologous groups.The simplest hydrocarbon is methane and it belongs to the alkane series.
5Homologous groupsA series of compounds with similar properties in which each member differs form the previous one by –CH2- is called a homologous groupMembers of the same homologous groups tend to have very similar chemical properties. So organising carbon compounds into homologous series simplifies the study of hydrocarbons.
6Alkanes Alkanes consist of carbon and hydrogen only. They contain only single bondsLook at the table, each alkane differs by –CH2-The alkanes have a general formula of CnH2n+2If a compound has 16 carbons, then 2 x = 34So it would have the fomula C16H34
7Representing alkane molecules When drawing hydrocarbons we use structural formulasThese are very similar to valence structures except they don’t show the unbonded pairs.In structural formulas we focus on the location of the atoms relative to one another in the molecule as well as the number and location of chemical bonds.
8The above diagram shows the first three alkanes. You will notice: Each carbon atom forms a single covalent bond to four other atomsEach hydrogen atom forms a single covalent bond to one carbon atomThe four atoms bonded to each carbon atom are arranged in a tetrahedral shape.
9Your TurnHow would we draw the structural formula for C4H10
10There are two possible ways. The first has the four carbon atoms in a continuous chain. The overall molecule is said to be linear.These are called straight-chain moleculesThe second one is not linear, this is called a branched chain molecule
11IsomerMolecules which have the same chemical formula but can form different arrangements of their atoms are called isomers.Same number of atoms just arranged differently.Structural isomers have similar chemical properties but can differ in some physical properties such as melting and boiling temperatures
12Alkanes The alkane series contains only single bonds. The alkanes are known to be saturated hydrocarbons as the carbons are saturated with hydrogensMeaning each carbon is completely bonded to either hydrogen or carbon, there are no unbonded carbons.
13Alkenes Alkenes contains one double bond between two carbons. Like alkanes, alkenes also differ by one –CH2- group.The alkenes also form a homologous series.The alkenes generally have the formulaCnH2n.
14Representing Alkene Molecules Like ethene, propene C3H6 also has one carbon-carbon double bond.
15Butene Butene (C4H8), like butane has more than one isomer. The alkenes are classified as unsaturated hydrocarbons. The double bond means that alkenes contain less hydrogen than the maximum amount possible.
16Semistructural formulas When we want to summarise the structural formula without indicating the 3D arrangement we use semistructural formulas.The semi structuralFormula for propene isC3H6
18Naming Carbon Compounds How do we name carbon compounds?How do we distinguish between structural isomers?There are a set of rules put in place by which chemists can derive a systematic name for a given compound.
19No of C atomsPrefix1meth-2eth-3prop-4but-5pent-6hex-7hept-8oct-9non-10dec-
20Straight-chain hydrocarbons The first part of the name refers to the number of hydrocarbons.The second part refers to type of bondsane if all carbon-carbon bonds are singleene if one C-C bond is a doubleyne if one C-C bond is a triplePentane, pentene and pentyne all have 5 carbons bonded in a linear or straight chain.
21Unsaturated compounds Unsaturated hydrocarbons contain at least one multiple bond.Butene has three isomers, two of which are straight chained, as the carbon chain becomes longer the number of isomers increases.To name straight-chain alkenes, first number the carbon atoms in the chain, starting with the end that will give the first carbon atom involved in the double bond the smallest number possible.
22The number starts at the end closest to the double bond. The isomer is named according to the first carbon atom involved in the double bond.The first isomer is but-1-ene.The other isomer is but-2-ene
23Branched Hydrocarbons An alkyl group usually forms a branch in a branched chain hydrocarbon.An alkyl group is an alkane molecule less on hydrogen atomIt is named after the alkane from which it is derived.-CH3 is a methyl group.-C2H5 (-CH2CH3) is an ethyl group
24Branched Hydrocarbons Systematic naming requires us to:Identify the longest continuous chain of carbon atoms in a molecule.Identify the side group that forms the branch in the chainNumber the carbon atoms from one of the ends of the longest carbon chain so that the side group is attached to the carbon atom with the smallest possible number.
25C4H10The longest chain of carbons has 3 carbons and all the bonds are single.Therefore the molecule is derived from propane.Identify the side groupThe side group is a methyl group.Number the carbons. The methyl group is on the second carbon.The compound is therefore 2-methylpropane.
30Chemical Properties of Alkanes The most significant reaction of alkanes is combustion. Alkanes burn in oxygen, releasing large quantities of energy.If the oxygen supply is sufficient the products released are carbon dioxide and water.This energy released is what we use as a source of heat, to produce electricity for domestic and industrial use.
31Equations for Combustion of Reactions This figure shows the rearrangement of atoms that occur when the hydrocarbon methane burns in oxygen.Have the atoms of each element been conserved?The equation isCH4 + 2O2 → CO2 + 2H2O
32Chemical Properties of Alkenes Due to the double bond in alkenes they react much more readily and with more chemicals than the alkanes.Alkenes, in particular, ethene and propene, are not used for fuels but rather as starting materials to manufacture a huge range of compounds such as alcohols, antifreeze and plastics.Apart from combustion, the reactions of alkenes usually involve the addition of a small molecule to produce a single product.
33Addition reactions of ethene Reaction with Bromine solutionEthene reacts with bromine solution as shown.In addition reactions, bonding “new” atoms to the two carbons on either side of the double bond, converts the C=C double bond to a C-C single bond.
34Reaction with SteamLarge amounts of ethanol are now made by the addition of steam and ethene using a phosphoric acid catalyst.This ethanol is used as a reagent for industrial purposes and as a solvent in cosmetics and pharmaceuticals.This is not the ethanol that people drink.
35Formation of polyethene An addition reaction of ethene is involved in making polyethene.As seen previously the C=C bond is converted to a C-C bond and a saturated product is formed.In this case there is no other reactant to add to the ethene molecules. Polyethene is formed when ethene molecules themselves join together to form a long chain.
36Polyethene is usually written as (-CH2-CH2-)n Where n is a large numberA molecule made by linking a large number of small molecules such as ethene is called a polymer (meaning many units). Each small molecule is called a monomer (one unit).This type of reaction is addition polymerisation
38Polymers Polymers are long chained molecules Each one can contain tens of thousands of atoms.Cotton, wool and silk are some naturally occurring polymers.Synthetically made polymers are generally superior to natural polymers as they have been designed for specific properties.
39Synthetic polymers Include: Check out table 8.8 on page 153 Cling wrap DrugsClothingDomestic appliancesCarsSporting equipmentCheck out table 8.8 on page 153
40Not PlasticWe frequently use the term plastic when referring to polymers.The term “plastic” refers to the property of a material not the material itself.A substance is “plastic” if it can be moulded into different shapes easily.Many polymers are indeed plastic, some however are not.The materials used to make powerpoints are brittle and cannot be reshaped.
41What are polymers? Polymers are large covalently bonded molecules. They contain tens of thousands of atomsThey are formed by joining together smaller molecular units called monomers.The size of the polymer varies, a polymer can consist of varying sizes of molecules formed from different numbers of monomers.
42Polymers There are two types of polymerisation processes. Addition polymerisationCondensation polymerisationThe polymers formed by addition polymerisation often have the monomer included in the name of the polymer.Polyethene is formed by the monomer ethene.Condensation polymers are named after the chemical bond they form.Polyesters contain monomers joined by an ester functional group
43Addition PolymersMost polymers are built around atoms of carbon like their monomers.Covalent bonds form between the monomers to produce a polymer molecule.
44Addition PolymersSuitable monomers for addition polymerisation are unsaturated molecules.What are unsaturated molecules?The double bond between the two carbon atoms react and new covalent bonds are formed between carbon atoms on nearby molecules creating long chains.
45PolyetheneRead page 155 – 156.Why is High-density polyethene stronger and more rigid than low-density polyethene?
46Structure, properties and applications Two very important properties of polymers are tensile strength and softening temperature.Tensile strength is a measure of the materials resistance to breaking under tension. It determines the structural uses of the polymer.The softening point affects the way the polymer can be moulded.Both tensile strength and softening point are determined by the strength of the forces between polymer chains.
47ThermoplasticsThermoplastics are polymers that can be moulded and shaped.The tensile strength and softening point are affected by:Degree of branchingNature of atoms of groups of atoms attached to the carbon chainHow the atoms or groups of atoms are arranged along the chain.
48Cross-linkingAnother factor that affects the properties of a polymer is cross-linking. A cross-link is a covalent bond between polymer chains.The more cross-links the stronger and rigid the polymer.The strong covalent bonds in 3D bind all the atoms together to form one large lattice.
49Thermosets Thermosets are polymers with extensive cross-linking. They do not soften on heating as thermoplastics do.When heat is applied the covalent bonds break and the thermosetting polymer will decompose rather than soften.
50Degree of branchingLow denisty polyethene contains a higher degree of branching which lowers the density, hardness and melting point of a polymer.Low denisty polyethene is more flexible and is used in cling wraps and squeeze bottles.High density polyethene is harder and less flexible, used in pipes and toys
51Nature of side groups Look at table 8.9 on page 156. Which are the bulky side groups which would lower density by getting in the way?These bulky side groups prevent the chains from stacking close together and forming strong rigid structures.
53Cross-linkingCross linking involves breaking the double bond in a polymer and using this double bond to bond to carbons in the next chain.
54Extensive cross-linking Where there is extensive cross-linking the structure will be rigid and cannot be re-shaped.Thermosetting polymers have extensive cross-linking.They char and burn when heated.They contain covalent bonds between the chains as well as within the chains
55Occasional cross-linking Elastomers are polymers that can be stretched or pulled out of shape and then will regain their original shape.They contain covalent bonds within the chains.They only contain a few covalent bonds between chains.They only have occasional cross-linking.
56Guess What We have finished unit 1 WOOHOO. be prepared for a topic test