Chemistry Term Exam Notes (Organic Chemistry) PDF

INTRODUCTION (4.1) Hydrocarbons ; molecules containing only hydrogen and carbon (4.2) Molecular formula shows the actual number of atoms of each element in a molecule. Empirical formula shows the simplest whole number ratio of atoms present in a compound. So the molecular formula is a multiple of th...

INTRODUCTION (4.1) Hydrocarbons ; molecules containing only hydrogen and carbon (4.2) Molecular formula shows the actual number of atoms of each element in a molecule. Empirical formula shows the simplest whole number ratio of atoms present in a compound. So the molecular formula is a multiple of the empirical formula. general formula shows the relationship between the number of atoms of one element to another within a molecule. Members of a homologous series share the same general formula. The general formula for alkanes is CnH2n+2 and the general formula for alkenes is CnH2n. structural formula shows how the atoms in a molecule are joined together. displayed formula is a full structural formula which shows all the bonds in a molecule as individual lines. Displayed formula: Molecular formula: C₄H₁₀ Empirical formula: C₂H₅ General formula (alkanes): CnH2n+2 Structural formula: CH₃ – CH₂ – CH₂ – CH₃ (4.3) Isomers are molecules with the same molecular formula but with a different structure. functional group is an atom or a group of atoms that determine the chemical properties of a compound. For example the functional group of an alcohol is the -OH group and that of alkenes is the C=C carbon to carbon double bond. Homologous series is a group of substances with: the same general formula similar chemical properties because they have the same functional group a trend (graduation) in physical properties (4.4) 1 Meth- 2 Eth- 3 Prop- 4 But- 5 Pent- 6 Hex- 7 Hept- 8 Oct- 9 Non- 10 Dec- Naming straight-chain alkanes The simplest hydrocarbons are alkanes. They contain only single bonds, and have “-ane” in the name. For example, the displayed formula of ethane (C₂H₆) is: Naming straight-chain alkenes Another simple group of hydrocarbons is the alkenes. They contain a carbon-to-carbon double bond, which also means they have two fewer hydrogen atoms than their corresponding alkane. An alkene has “-ene” in its name. For example, the displayed formula for ethene (C₂H₄) is: With longer alkene molecules the double bond might appear in different locations of the carbon chain, so the name needs to be a little bit more complicated to be able to describe these differences clearly. A number is added in the middle of the name to indicate at which carbon the double bond starts. So the displayed formula of pent-1-ene is: 9 (4.5) DISPLAYED FORMULA: Formula that graphically shows the number of atoms of each element in compound and the bonds that join them together (straight lines representing covalent bonds) STRUCTURAL FORMULA: Formula that states the number of atoms of each element in compound and the bonds that join them together (straight lines representing covalent bonds. (4.6) SUBSTITUTION REACTION: Reaction where one atom is swapped with another atom Example: Methane reacts with Bromine under Ultraviolet Light ADDITION REACTION: Reaction in which one molecule combines with another to form a single larger molecule Example: Bromine will react with Ethene by Bromine molecule adding across the double bond of Ethene COMBUSTION REACTION: Chemical reaction involving burning sExample: Alkenes burn when heated in Air of Oxygen (b) CRUDE OIL (4.7) crude oil: mixture of hydrocarbons (4.8) FRACTIONAL DISTILLATION: Method to separate two or more liquids that are miscible with one another. (4.11) a fuel is a substance that when burned releases energy (4.12) complete combustion occurs when there is enough oxygen available for the fuel to react, producing CO2 and H20 E.G CH4 + 2O2 ——— CO2 + 2H2O (4.13) Carbon monoxide is produced from incomplete combustion of fuels E.G Propane + oxygen ——— carbon monoxide + water (4.14) When fuels are burned in vehicle engines, high temperatures are reached. At these high temperatures. Nitrogen and oxygen produce oxides. Nitrogen + oxygen ——— nitrogen oxides In the atmosphere nitrogen oxides can combine with water to create nitric acid ( acid rain , corrosive) (4.15) Fossil fuels like coal , gas and oil are derived from crude oil , these fuels are hydrocarbons , but also include impurities like sulfur. When these fuels are burned , sulfur dioxide is made which csm escape into the atmosphere. S(s) + O2 (g) —— SO2 (g) ALKANES (4.19) general formula for alkanes CnH2n+2 -This means that to work out the number of hydrogens , you double the number of carbons and then add 2. (4.20) - saturated; molecule containing only single bonds between carbon atoms. e.g allanes are described as saturated molecules - unsaturated; molecule containing a carbon-carbón double bond e.g alkanes are described as unsaturated molecules (4.21) ISOMERS: Compound that has same molecular formula but different displayed formulae Methane : Ethane: Propane: Butane: Pentane: (4.22) Alkanes react with bromine in the presence of ultraviolet radiation A hydrogen atom is replaced by a bromine atom , this called substitution Methane + bromine ————— bromethane + hydrogen bromine ALKANES (4.23) alkanes are a homologous series if hydrocarbons that contain a c=c double bond. The alkanes that end with “ene” I.e ethene CH2 = CH2 - molecules with more than 2 carbon atoms can cause the position to vary. (4.24) general formula for alkanes CnH2n An alkane always has to have twice as many hydrogen atoms as carbon atoms. (4.26) Ethene: Propene: Butene: (4.27) Alkanes react with bromine water , uv light is NOT required. The double bomd is broken and the bromine atoms are added , this is addition. During this reaction there is a colour change from orange to colourless. (4.28) Presence of double bond (C=C) allows Alkenes to react in ways that Alkanes cannot, therefore allowing Alkenes and Alkanes to be identified using chemical test: Test to distinguish alkane and alkene