VCE Chemistry Unit 3 Outcome 2 Notes

Outcome 2Organic Chemistry

Compounds of CarbonCarbon chemistry/organic chemistry The study of carbon compounds (excluding oxides of carbon, carbonates, carbides and cyanides)

Hydrocarbons Molecules made up of only hydrogen and carbon Non-polarThe strength of the dispersion forces is greater when The molecules are closer to one another The molecules are larger

Isomers Molecules that have the same molecular formula but different structural formulas Isomers are different compounds that can have different chemical and physical properties e.g. melting points an boiling points

Properties of HydrocarbonsElectrical Properties Since hydrocarbons consists of uncharged molecules and have no delocalized electrons, they cannot conduct electricityMelting and Boiling points The greater the amount of energy needed to move the molecules past each other and out of the solid lattice. Therefore the greater the melting and boiling points of the solidSolubility Because hydrocarbons are non polar they are soluble in other non polar solutions Not very soluble in polar substance (e.g. water)Combustion Reactions Many hydrocarbons are highly flammable They readily burn in air producing carbon dioxide and water and a significant amount of energy The heavier the hydrocarbon, the more dispersion forces, the more energy required, the less flammable

Alkanes Family of hydrocarbons only containing single bonds between the carbon atoms Saturated hydrocarbons The name of each alkane ends in ane They have a general formulas CnH2n+2 Alkanes are known as an homologous series (series of organic compounds in which each successive member differs by CH2- from the previous one

Alkenes Family of hydrocarbons only containing double bonds between the carbon atoms Unsaturated hydrocarbons The name of each alkane ends in ene They have a general formulas CnH2nEthene which is the smallest member of the alkene family is Unsaturated Non-polar Insoluble in water Has a boiling point of -104C A flammable gas

The Bromine Test To test where a hydrocarbon is saturated or unsaturated Bromine solutions are reddish brown but when mixed with an unsaturated hydrocarbon the reddish brown colour will disappear E.g. Br2 (red/brown) + Unsaturated Alkene (colourless) C2H4Br2 (colourless) Whereas e.g. Br2 (red/brown) + Saturated Alkane (colourless) Red/Brown

Cyclic Molecules A chain of cyclic molecules can also be bent to form a ring The molecules formed in this way are called cyclic molecules The general formula for cycloalkanes is C2H2n

Benzene In benzene, three of the four outer shell electrons from each carbon atom from normal covalent bonds The fourth electron is shared (delocalized) around the six membered carbon ring In total there are 6 delocalized electrons per benzene molecule which are effectively shared by the six carbon atoms Compounds like this are called arenes

Functional GroupsA functional group is an atom or a group of atoms that give a characteristic set of chemical properties to a molecule that contains that group

Haloalkanes One of the hydrogen on the carbon chain is replaced by a chlorine atom The prefix chloro is added to the name of the alkane Halogens that can be added to the hydrocarbon chain: Fluorine (fluoro), iodine (iodo) and bromine (bromo) Chlorine is a polar functional group, chloroalkanes are more reactive than their parent alkane Halogens are highly electronegative, thus they alter the physical properties of the haloalkane, making the molecule more soluble in polar solvents

Alcohols/Alkanols One of the hydrogen on the carbon chain is replaced by an OH group The e at the end of the name of the alkane is replaced with ol Due to the presence of the OH functional group which is polar, alcohols are more soluble in water than alkanes The smaller alcohols are more soluble than the larger ones due to less dispersion forces Alcohols also have higher boiling points than alkanes of similar size The OH functional group is called hydroxy or hydroxyl

Carboxylic acids The three hydrogens at the end of the carbon atom are replaced by a doubled oxygen and an OH group The e in the ane of the alkane is replaced with oic acid Smaller carboxylic acids will dissolve in water by forming hydrogen bonds Larger carboxylic acids will tend to form a separate layer on the water surface The COOH functional group is called carboxy or carboxyl

Amines One of the hydrogen on the carbon chain is replaced by an NH2 group Named by adding the suffix amine to the name of the alkyl group or by adding anamine to the stem name e.g. butylamine or butanamine The smaller amines are very soluble in water due to the formation of hydrogen bonds The solubility decreases as the size of the molecule becomes larger, as the more hydrogens present, the larger the compound and the less polar the overall molecule becomes, thus less soluble Primary amines NH2Secondary Amines NHTertiary Amines N

Reaction PathwaysThe stability of the carbon-carbon single bonds and the non-polar nature of the molecules mean that alkanes are very resistant to reactions. Most reactions involving alkanes are either combustion or substitutionCombustion Reaction Many hydrocarbons are highly flammable They readily burn in air producing carbon dioxide and water and a significant amount of energy (thus many are used for fuels) In general the heavier the hydrocarbon, the less flammable it is due to the increase in dispersion forces

Substitution Reaction One or more of the hydrogen atoms in an alkane are replaced by a different atom(s) This involves breaking the carbon-hydrogen bond and making new bonds with the substituting atom or group of atoms

Chloroethane Chloroethane is a gas at room temperature It can be produced by heating mixtures of chlorine and ethane or it can be initiated by exposing the gas mixture to ultraviolet light In each situation the reaction conditions result in the chlorine molecule breaking into separate Cl atoms which are unstable and will attack the carbon-hydrogen bonds in the ethane The chloroalkane that is produced can be a mixture of different compounds (C2H5Cl C2Cl6)

Addition Reactions Due to the presence of the double bond, which is more reactive due to the more available electrons, ethane reacts more readily and with more chemicals than ethane The reactions of ethane usually involve addition of a small molecule to produce a single product During addition reactions the double carbon-carbon bond is broken and converted to a single bond Ethene can react with bromine to produce bromoethaneH2C=CH2(g) + Br-Br(g) CH2BrCH2Br(g) Ethene can react with hydrogen chloride to produce chloroethane H2C=CH2(g) + H-Cl(g) CH3CH2Cl(g) Ethene can react with steam to produce ethanol H2C=CH2(g) + H2O(g) CH3CH2OH(g) This reaction takes place in the presence of the catalyst H3PO4. This reaction is a one step process which requires very little energy apart form initial heating and is called a hydrolysis reaction (involves H2O breaking down)

Addition Polymerisation Polyethene Formed by an addition polymerization reaction from ethane

High Density Polyethene