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Definitions AG Energy level • is the fixed energy value that an electron in an atom may have. AG An orbital • is a region in space within which there is a high probability of finding an electron. AG An element • is a substance that cannot be split up into simpler substances by chemical means. AG A triad • is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two. (Dobereiner) AG Newlands’ Octaves • are groups of elements arranged in order of increasing atomic weight, in which the first and the eighth element of each group have similar properties. AG Mendeleev’s Periodic Law • When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically. AG The atomic number(Z) • is the number of protons in the nucleus of that atom. AG Periodic Table • is an arrangement of elements in order of increasing atomic number. AG Elements are arranged • in order of increasing atomic number, the properties of the elements vary periodically. AG Mass number (A) • is the sum of the number of protons and neutrons in the nucleus of an atom of that element. AG Isotopes • are atoms of the same element ( i.e. they have the same atomic number) that have different mass numbers due to the different number of neutrons in the nucleus. AG Relative Atomic Mass • is the average of the mass numbers of the isotopes of the element • as they occur naturally • taking their abundances into account • expressed on a scale in which the atoms of carbon 12 isotope have a mass of exactly 12 units. AG Mass Spec. • • • • • V I A S D Vaporisation Ionisation Acceleration how? why? Separation Detection A+ Victor AG Aufbau Principle • that when building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level. AG Hund’s Rule of Maximum Multiplicity • states that when two or more orbitals of equal energy are available, the electrons occupy them singly first before filling them in pairs. AG Pauli Exclusion Principle • that no more than two electrons may occupy an orbital and they must have opposite spins. AG Compound • is a substance that is made up of two or more different elements combined together chemically. AG Octet Rule • that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell. AG An Ion • is a charged atom or group of atoms. AG An Ionic bond • is the force of attraction between oppositely charged ions in a compound. AG A transition metal • is one that forms at least one ion with a partially filled d sublevel. AG Molecule • is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently. AG Valency of an element • is defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines. AG Electronegativity • is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond. AG Electronegativity • difference > 1.7 indicates ionic bonding in a compound. • An electronegativity difference ≤ 1.7 indicates covalent bonding in a compound. AG The value of electronegativity • decrease down the groups in the Periodic Table for two reasons: • increasing atomic radius • screening effect of inner electrons AG The values of electronegativity • increase across the periods in the Periodic Table for two reasons: • increasing nuclear charge • decreasing atomic radius F= most electronegative element. Halogens –decrease in reducing power down the group due to drop in electroneg. values. AG Vans der Waals Forces • are weak attractive forces between molecules resulting from the formation of temporary dipoles. AG Dipole-dipole • Dipole – dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another. AG Hydrogen bonds • are particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. • The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule. Thus, H acts as a bridge between two electronegative atoms. AG The Law of Conservation of Mass • the total mass of the products of a chemical reaction is the same as the total mass of the reactants. AG The Law of Conservation of Matter • that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another. AG Tests for Anions • • • • • Chloride Sulfate/sulfite carbonate/hydrogen carbonate nitrate phosphate • (NB know confirmatory test too!) AG Chloride • Add AgNO3 • Get white ppt • Confirm = ppt dissolves in dilute ammonia • Equation needed AG Sulfate/sulfite • Add BaCl2 • Get white ppt • Distinguish • add dil HCl to white ppt • ppt remains = sulfate • ppt dissolves = sulfite AG Equation needed !! CO32- /HCO3• Add dil. HCl (or any acid) • Get bubbles of CO2 (limewater milky) • Distinguish • add MgSO4 to fresh solution • Get white ppt. immediately = carbonate white ppt on heating = hydrogen carbonate Equation needed !! AG Nitrate • Brown Ring Test • Add fresh FeSO4 At slant add conc. H2SO4 drop wise • Get brown ring at junction of 2 layers No equation needed AG Phosphate • Add ammonium molybdate • Add 5 drops of conc. nitric acid • Get yellow ppt (warm the solution) ?Query confirm’y test No equation needed AG The atomic radius of an atom • is defined as half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond. AG The values of atomic radius • increase down any one group in the Periodic Table for two reasons: • extra shell • screening effect of inner electrons AG The values of atomic radius • decrease from left to right across a Periodic Table for two reasons: • increasing nuclear charge • no increase in screening effect AG The first ionisation energy of an atom • is the minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in the ground state.****** • • 2004 =9 marks (2.25%) 2002 = 8marks(2%) AG The values of ionisation energy • decrease down the groups in the Periodic Table for two reasons: • increasing atomic radius • screening effect of inner electrons AG The values of ionisation energy • increase across the Periodic Table for two reasons: • increasing nuclear charge • decreasing atomic radius AG More on ionisation energy • First Ionisation Energy • M – e- M+ • Second Ionisation energy M+ – e- M2+ Major jump in I.E. values – significance AG The value of electronegativity • decrease down the groups in the Periodic Table for two reasons: • increasing atomic radius • screening effect of inner electrons AG The values of electronegativity • increase across the periods in the Periodic Table for two reasons: • increasing nuclear charge • decreasing atomic radius F= most electronegative element. Halogens –decrease in reducing power down the group due to drop in electroneg. values. AG A gas • is a substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed. AG Radioactivity • is the spontaneous breaking up of unstable nuclei • with the emission of one or more types of radiation. AG Alpha particles • • • • loss of He nucleus (2p + 2n) mass number down by 4 atomic number down by 2 element changes to element two places back AG Beta particle • neutron changes to proton and electron • electron emitted • mass number stays same • atomic number drops by one • element changes into element one place back AG Gamma radiation • no new atoms formed • (no transmutation) • only energy lost AG Half Life • of an element is the time taken for half the nuclei in any given sample to decay. AG Mole • is the amount of a substance which contains 6 X 1023 particles of that substance • (avogadro’s number or constant =L) AG a few numbers • Kelvin = Celsius + 273 • standard temp = 273 K • standard pressure = 1X105 Pa (100kPa) m3 = litres X10 -3 m3 = cm3 X10 -6 (1 litre = 1000cm3) AG Mole • contains 6 X 1023 particles • has mass equal to Ar or Mr in grams • occupies 22.4 litres at s.t.p (if gas) AG Boyle’s Law • states that: at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure. AG Charles’ Law • states that: at constant pressure, the volume of a fixed mass of a gas is directly proportional to its temperature measured on the Kelvin scale. AG General Gas Law • P1 X V1 = P2 X V2 T1 T2 Temp in Kelvin Units for volume same each side Units for pressure same each side AG Gay Lussac’s law of Combining Volumes • the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temp and pressure AG Avogadro’s Law • states that • equal volumes of gases contain • equal numbers of molecules under the same conditions of temp. and pressure AG Molar Volume • At s.t.p • one mole of any gas • occupies 22.4 litres • Remember to watch out for r.t.p in questions • room temp. and press = as given in Q • (often 24 litres) AG Ideal Gas • is one which perfectly obeys • all the gas laws and all the assumptions* of the kinetic theory of gases • under all conditions of temperature and pressure. • (Know the assumptions) AG Real v. ideal gas • Real gases differ from ideal gases at high pressure and low temp. because • there are forces of attraction/repulsion between the molecules* • the volume of the molecules is not negligible compared to the distances between them (*know examples of real gases and the forces involved) AG Empirical Formula • gives the simplest whole number ratio of the numbers of the different atoms present in the molecule. (divide by Ar and get ratio) (molecular formula is a simple multiple of the empirical formula) AG Acids / Bases • • • • • Arrhenius Acid + Base Bronsted Lowry Acid + Base Neutralisation Conjugate Acid/ conjugate base conjugate pair AG Arrhenius Acid and Base • Arrhenius Acid • is a substance that dissociates in water to produce H+ ions. • Arrhenius Base • is a substance that dissociates in water to produce OH- ions. AG Bronsted Lowry Acid /Base • Bronsted Lowry Acid • is a proton (H+) donor • Bronsted Lowry Base • is a proton (H+) acceptor AG Neutralisation • is the reaction between an acid and a base • forming a salt and water (acid + base -> salt + water) SALT = is formed when the H of an acid is replaced by a metal AG Conjugate Acid / Conjugate Base • Conjugate Acid is formed when a base accepts a proton • Conjugate Base • is formed when an acid donates a proton. AG Conjugate Pair • an acid and a base that differ by a proton AG Primary Standard • is a substance which can be obtained in a pure stable soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration. • (Know why high Mr matters) AG Titration • is a laboratory procedure where a a measured volume of one solution is added to a known volume of another solution until the reaction is complete. • (concentration of one solution known accurately at start) • (indicator used to show by colour change when reaction is complete) AG Oxidation Reduction Revision AG Definitions • Oxidation is • addition of • loss of • increase in oxygen Electrons or hydrogen oxidation number AG • Reduction is • loss of oxygen • gain of electrons • decrease in oxidation number AG More… • An oxidising agent causes oxidation and is itself reduced. • A reducing agent causes reduction and is itself oxidised. • What is a redox reaction? AG What is oxidised and reduced in each of the following? • Br2 + 2Fe 2+ → 2Br– + 2Fe 3+ • Cu 2+ + Zn Cu + Zn 2+ • 2Na + Cl2 2NaCl AG Oxidation Number Rules • The oxidation number of • an Element is 0 • group One elements is +1 • group Two elements is +2 in compounds AG The oxidation number of an ion is equal to the charge on the ion • halogens is -1 (in binary compounds) (except ……????) AG • The oxidation number of H in a compound is +1 – except in metal hydrides when it is -1 AG • The oxidation number of O in a compound is -2 – except (x2) in peroxides when it is -1 (H2O2) in OF2 when it is +2 (why?) AG • Oxidation numbers • add up to zero in a compound • add up to the charge of a complex ion AG • What is the oxidation number of each element in :H20 MnO4¯ I2 KBrO3 Na2S2O3 H2O2 NaClO AG KMnO4 • • • • oxidising agent purple read top of meniscus is reduced from Mn (VII) Mn (II) in presence of H+ purple colourless • own indicator (end point = first permanent pink) AG KMnO4 • get brown Mn (IV) if H+ absent • (which acid MUST be used – why x2) • not primary standard (x2) • standardised by titrating against standard solution of acidified Fe 2+ AG H2SO4 • added during KMnO4 titrations to provide H+ and ensure the complete reduction of Mn (VII) Mn (II) and prevent formation of Mn (IV) (brown) • added during prep. of Fe (II) solutions to prevent oxidation of Fe 2+ to Fe 3+ by oxygen in the air ( why does this matter?) AG Na2S2O3 • S2O3 2- ion • reducing agent • used in photography • not primary standard – why ? • standardised by titrating against I 2 • starch indicator – when added and why • colour change at end point ? AG Iodine I2 • Oxidising agent • NOT a primary standard (X2) • Produced when MnO4- oxidises » (known concentration) I- to I2 (in excess) • Starch indicator – when added? why then? • Colour change at end point Blue/black to colourless AG Bleach • sodium hypochlorite Na+ClO• bleach diluted x10 with distilled water not de-ionised water (why? ) NB • ClO- oxidises I- to I2 • I2 v. thiosulfate remember dilution factor in calculations • starch indicator as before AG Rates of Reactions • The rate of reaction is the change in concentration per unit time of any one reactant or product. AG Factors affecting rate • nature of reactants • particle size • concentration • temperature • catalysts AG Rate Graphs • Concentration v. ( 1 /Time ) • or • Temp v. ( 1 /Time ) • ( 1 /Time )used as Rate and Time inversely related • (shorter time means faster rate) • be careful with units of 1/time AG Catalyst • is a substance that alters the rate of reaction • but is not consumed in the reaction. AG Homogeneous catalysis • occurs when the reactants and the catalyst are in the same phase. • example =? AG Heterogeneous catalysis • occurs when the reactants and the catalyst are in different phases. • example = ? AG Autocatalysis • occurs when one of the products of the reaction catalyses the reaction. • Example = ? AG Mechanism of Catalysis • Intermediate Formation theory • Surface Adsorption theory AG Catalytic converter • Catalysts = Pt + Pd + Rh • Gases in CO NO NO2 hydrocarbons • Gases out CO2 and N2 and H20 AG Collision Theory • for a reaction to occur the reacting particles must collide with each other • a collision only results in a product being formed if a certain minimum energy is exceeded (called activation energy) AG Activation Energy • is the minimum energy which colliding particles must have for a reaction to occur. AG Chemical Equilibrium • is a state of dynamic balance where the rate of the forward reaction equals the rate of the reverse reaction. AG Le Chatelier’s Principle • If a stress is applied to a system at equilibrium • the system readjusts to oppose the stress applied AG Le Chatelier’s Principle and Gases • Le Chatelier’s Principle predicts that in an all-gaseous reaction an increase in pressure will favour the reaction which takes place with a reduction in volume • ( towards the side with the smaller number of molecules) AG Equilibrium Constant • Kc [ ] means concentration in moles per litre [ C] c x [D]d Kc = ----------------[A]a x [B]b for aA + bB cC + dD (products of products conc. over product of reactants conc.) AG Le Chatelier and Industry • Ammonia and Haber Process predict max yield at high press. /low temp reality = 200 atm and 500o C • Sulfuric Acid and Contact Process predict max yield at high press. /low temp reality = one atm and 450oC AG Kc • large Kc => equilibrium far to right (lots of product produced) • small Kc => equilibrium far to left (v. little product formed) • must quote temp. • units – depend on reaction • tells us how far not how fast a reaction occurs AG pH • pH = -log [H+] [ ]= moles per litre • pH < 7 acid • pH = 7 neutral • pH > 7 base AG Kw • Kw = [H+].[OH-] ([H+] = √Kw) • Kw = 1x10-14 ( at 25oC) AG Strong / Weak acid • A strong acid is one which is fully dissociated in solution • [H+] = [acid] HCl • [H+] = 2x[acid] H2SO4 etc • A weak acid is one which is not fully dissociated in solution • [H+] = √Ka x Macid AG Strong / Weak base • A strong base is one which is fully dissociated in solution • [OH-] = [base] NaOH • [OH-] = 2x[base] Ca(OH)2 etc • A weak base is one which is not fully dissociated in solution • [OH-] = √Kb x Mbase AG Indicator • An acid base indicator is a substance that changes colour according to the pH of the solution it is in. • (equilibrium HIn ↔ H+ + In-) AG Methyl orange • in acid (lower pH ) red • in base ( higher pH) yellow • range pH 3-5 AG Phenolphthalein • in acid (lower pH ) colourless • in base ( higher pH) pink • range pH 8-11 AG Litmus • in acid (lower pH ) red • in base ( higher pH) blue • range pH 5-8 (Not as reliable as others for accurate work) AG Which indicator ? • strong acid/strong base = methyl orange / phenolphthalein /litmus( see above) • strong acid / weak base = methyl orange • weak acid /strong base = phenolphthalein • weak acid / weak base = none (why?) AG Hard Water • is water that will not easily form a lather with soap • due to the presence of Ca 2+ or Mg 2+ ions in solution. AG Temporary Hardness • • • • can be removed by boiling the water due to Ca(HCO3)2 becomes CaCO3 on heating leads to blocked pipes etc AG Permanent Hardness • is not removed by boiling the water • caused by CaSO4 or MgSO4 AG Methods of removing hardness • boiling (only works for temp. hardness) • distillation • washing soda • ion exchange AG Calculations • Total hardness = calcium hardness + magnesium hardness but • Do calculations as if all hardness caused by CaCO3 • expressed in p.p.m of CaCO3 • p.p.m. = mg/litre AG Water Treatment • • • • • • • screening flocculation sedimentation filtration chlorination fluoridation pH adjustment AG B.O.D • Biochemical Oxygen Demand is the amount of dissolved oxygen consumed by biological action when a sample of water is kept at 20oC in the dark for five days. (know reason for each of 3 conditions) AG Eutrophication • is the enrichment of water with nutrients which leads to the excessive growth of algae. • Nutrients – phosphates/nitrates • Algal bloom / oxygen depletion AG Sewage Treatment • Primary Treatment physical • Secondary Treatment biological • Tertiary Treatment chemical AG Water Analysis • Atomic Absorption Spectrometry used to detect heavy metals like Cd, Hg, Pb • pH meter • colorimetry (Hach test Chlorine in pool water) AG Electrolysis • is the use of electricity to bring about a chemical reaction. • KI/ Acidified water/ Na2SO4/CuSO4 / ions AG Electrolyte • is a substance that conducts electricity as a result of the presence of ions. AG Electroplating • is the process where electrolysis is used to put a layer of one metal on the surface of another. AG Electrochemical Series • is a list of the elements in order of their standard electrode potentials. AG Organic Chemistry • is the study of compounds of carbon… (except some simple compounds like CO2, CO and carbonates) AG Hydrocarbon • is a compound that contains only carbon and hydrogen • includes alkanes, alkenes, alkynes • excludes alcohols, aldehydes, ketones, carboxylic acids, esters AG Saturated compound • is one with only carbon – carbon single bonds • alkanes AG Unsaturated compound • is one which contains carbon – carbon double or triple bonds • alkenes / alkynes • test for unsaturation decolourise bromine solution AG Homologous Series • is a series of chemical compounds of uniform chemical type • showing gradations in physical properties • having a general formula for its members • each member has similar method of prep. and • each member differs by (CH2) from previous member AG Structural isomers • are compounds with the same molecular formula but different structural formulas. • e.g. butane and methyl propane are both C4H10 • need to know isomers up to C5H12 AG Aliphatic • an aliphatic compound is an organic compound that consists of straight (open) chains of carbon atoms and closed chain compounds with similar properties. AG Aromatic • An aromatic compound is an organic compound that contains a benzene ring structure in their molecules. (benzene – delocalised double bond) (disc. by Michael Faraday ) (structure by Kekule) AG Octane Number • of a fuel is a measure of the tendency of the fuel to resist knocking. (Best fuels = high octane number = 100 = 2,2,4 tri methyl pentane ) (Short chains, more branched chains, ring structures) (Worst fuels = low octane number =0 = heptane) AG Ways to increase octane number • isomerisation • catalytic cracking • dehydro-cyclis-ation (re-forming) • add oxygenates AG Isomerisation • changing straight chain alkanes into branched chain alkanes AG Catalytic cracking • is the breaking down of long chain hydro- carbon molecules into short chain molecules (for which there is a greater demand) AG Dehydrocyclisation ( Re-forming) • involves the use of catalysts to form ring structures • straight chain alkanes changed to cycloalkanes • cycloalkanes changed to aromatic compounds • petrol contains benzene = carcinogen • health concerns AG Adding Oxygenates addition of • methanol • ethanol • MTBE to petrol to increase the octane number. (Methyl Tertiary Butyl Ether or 2 methoxy 2 methyl propane) AG Exothermic reaction • is one which produces heat. • ∆H is minus ( giving away) AG Endothermic reaction • is one which takes in heat. • ∆H is positive (add in) • ammonium nitrate dissolving in water AG Heat of Reaction • is the heat change involved when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely. AG Heat of Combustion • is the heat change involved when one mole of a substance is completely burned in excess oxygen AG Kilogram Calorific Value • of a fuel is the heat energy produced when 1 kg of a fuel is completely burned in oxygen. AG Bond Energy • is the energy required to break one mole of covalent bonds and to separate the neutral atoms completely from each other. AG Heat of Neutralisation • is the heat change involved when one mole of H+ ions from an acid reacts with one mole of OH- from a base forming one mole of H2O AG Heat liberated • Heat liberated = M x C x Rise in temp. Kg kelvin • M=Mass of solution in Kg • c=specific heat capacity • rise in temp in Kelvin AG Heat of formation • of a compound is the heat change involved when one mole of a compound in its standard state is formed from its elements in their standard states. AG Hess’s Law • states that if a chemical reaction takes place in a number of stages, the sum of the heat changes in the separate stages is equal to the heat change if the reaction is carried out in one stage. (overall heat change is independent of the pathway) AG Law of Conservation of Energy • states that energy cannot be created or destroyed but can be changed from one form of energy to another. AG Functional Group • is an atom or group of atoms which is responsible for the characteristic properties of a series of organic compounds. AG Substitution Reaction • is a chemical reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms • mechanism = free radical substitution initiation (homolytic fission) propagation termination AG Addition Reaction • is a chemical reaction is which two substances react together forming a single substance. • Mechanism = Ionic addition • Approach/ polarisation / heterolytic fission /carbonium ion / product formation • only happens to unsaturated compounds AG Polymers • are long chain molecules made by joining together many small molecules called monomers. AG Elimination reaction • is one in which a small molecule is removed from a larger molecule to leave a double bond in the larger molecule. AG Organic Synthesis • is the process of making organic compounds from simpler starting materials. AG Chromatography • is a separation technique in which a mobile phase carrying a mixture moves in contact with a selectively adsorbent stationary phase. AG Instrumentation • • • • • • • Mass Spec. AAS GC HPLC IR spec. UV spec. X ray crystallography (option 2) AG Principles Mass Spec. Processes • Positively charged ions are separated • according to different relative masses • when moving through magnetic field Vapourisation Ionisation Acceleration Separation Detection A+ Victor Used to Analyse blood of race horses for drugs Identify substances AG Atomic Absorption Spectrometer Principles • Ground state atoms of an element absorb light characteristic of that element. • Absorption is directly proportional to concentration. • (higher absorbance means higher concentration of THAT ELEMENT present) Processes Dissolve Atomise Absorb Measure Detection Used to analyse water samples for heavy metals Cd Hg Pb AG Gas Chromatography GC Principles Processes • Different components have different tendencies to dissolve in a nonvolatile liquid, which is coated on fine particles of a solid in a the GC column mobile phase ? ? stationary phase? Injection … Transport … Separation … Detection ... Used with MS in drug testing also blood alcohol levels AG HPLC Principles Processes • High Performance Liquid Chromatography • Different components of a mixture have different tendencies to adsorb onto fine particles of solid in HPLC column mobile phase ? ? stationary phase? Injection … Transport … Separation … Detection … Used to separate less volatile mixtures e.g. growth promoters in meat. AG IR Principles • Infra red spectrometry • Molecules of a substance absorb infra –red of different frequencies. (different number/ type bonds) • The combination of frequencies absorbed is peculiar to the molecules of each substance Processes Prepare … Transmit IR Absorption… Detection… Spectrum obtained Used to identify functional groups and identify drugs AG UV Principles • Ultra violet spectrometry • Molecules absorb UV radiation • Electrons promoted from ground state to higher energy states. • Absorption is directly proportional to concentration. Processes Prepare Transmit UV through Blank (o%abs) Sample (known + unknown) Spectrum obtained Quantatative used to find amount of org. subs. e.g. drugs AG X ray crystallography Principles • Wavelengths of Xrays are comparable to distance between atoms in a crystal • Xrays are scattered when they hit a crystal surface • Pattern detected is analysed and structure worked out Processes Prepare …. Transmit : x-ray detected on film Pattern analysed and structure worked out Used to determine structure of macromolecules e.g. DNA AG