CIEAS 化学笔记考试核心考点速记.pdf

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1、CIE AS LEVEL- CHEMISTRY 9701 Page 3 of 27 1. ATOMS, MOLECULES AND STOICHIOMETRY 1.1 Relative Mass Rel ati ve Atomic mass (Ar): weighted average mass of an atom compared with 12C where one atom of 12C has mass of exactly 12 units Molecular mass (Mr): mass of a molecule Formula mass: mass of one formu

2、la unit of a compound Isotopic mass: mass of a particular isotope of an element 1.2 The Mole Mole: amount of substance that has the same number of particles (atoms, ions, molecules or electrons) as there are atoms in exactly 12g of the carbon-12 isotope. Avogadros constant: number of atoms, ions, mo

3、lecules or electrons in a mole = 6.021023 1.3 Mass Spectra Abundance of isotopes can be represented on a mass spectra diagram = 100% = 100 1.4 Empirical and Molecular Formulae Empirical formula: gives simplest ratio of different atoms present in a molecule Molecular formula: gives actual numbers of

4、each type of atom in a molecule Molecular formula can be calculated using the Mr of a compound and its empirical formula = ( ) Where = % = . 100% 1.5 Calculations involving Mole Concept = = 24 Formula applies to gases at r.t.p. Unit of volume is 3and 10003 = 13 = Concentration unit = 3 2. ATOMIC STR

5、UCTURE 2.1 Subatomic Particle Subatomic Particle Relative Charge Relative mass/ a.m.u Protons (P) +1 1 Neutrons (n) 0 1 Electrons (e-) -1 1/1840 2.2 Behavior of a Beam of Subatomic Particles Protons: positively charged deflected to -ve pole Neutrons: no charge not deflected Electrons: negatively cha

6、rged deflected to +ve pole e- lighter than P+ deflected at greater angle 2.3 Protons, neutrons and electrons Mass concentrated within center; nucleus An atom is electrically neutral; P+ = e- Atomic no. or proton no. (Z) = no. of protons Atomic mass or nucleon no. (A) = no. of P + N Isoelectronic ion

7、s: ions having same no. of e-s Isotopes: are atoms of the same element with the same proton number but different number of neutrons 2.4 Electronic Configuration Electrons are arranged in energy levels called shells Each shell is described by a principle quantum no. (P.Q) As the P.Q. increases, energ

8、y of shell increases Inside the shell there are subshells: , and Orbital: region in space where there is a maximum probability of finding an electron Each orbital can hold 2e-s in opposite directions CIE AS LEVEL- CHEMISTRY 9701 Page 4 of 27 When e-s are placed in a set of orbital of equal energy, t

9、hey occupy them singly and then pairing takes place e-s placed in opposite direction: both -vely charge distance of outermost e- to nucleus is large less energy needed to remove e- Sta ble Co nfi g. High I.E needed to remove e-s from completely or half-filled orbitals 2.9 General 1st I.E Trends Firs

10、t Ionization Energy Trends Down a Group Across a Period DECREASES New shells added Attraction of nucleus to valence e-s decreases Shielding effect increases INCREASES Shell no. remains same Proton no. increases Effective nuclear charge increases Atomic radius decreases 2.10 Trend in 1st I.E Across 3

11、rd Period I.E of Al lower than Mg: e- removed in Al is from higher energy 3p orbital which is further away from nucleus than 3s e- being removed from Mg. Nuclear attraction is less for 3p than 3s I.E of Al is lower than Mg I.E of S lower than P: e- being removed in P is in a half filled, more stable

12、 3p orbital whereas in S, the pairing of electrons in 3p results in increased repulsion less energy need to remove an e- Big jump occurs between I.E 1 larger the radius, longer the bond length Strength of the bond depends on the length of the bond 3.9 Polar and Non-Polar Polar Covalent Bonds Bonds w

13、ith slight ionic character Bond formed with atoms of different electronegativity Bonding e-s attracted more towards atom with greater electronegativity unequal sharing of electrons molecule develops slight charges = Polar Molecule Polar molecules have dipoles; electric charges of equal magnitude and

14、 opposite sign The greater the difference in electronegativity of the two bonded atoms, the greater is the ionic character Non-Polar Covalent Bonds Bond formed between: o Identical atoms: the electronegativity of both atoms is the same so pair of electron shared equally o Symmetrical polyatomic mole

15、cules: dipoles of bond exert equal point where molecules come close together o increasing number of electrons (+ protons) in molecule Permanent Dipole-Dipole Forces Weak forces present between polar molecules Molecules always attracted to charged rod, whether +ve or ve because molecules have +ve and

16、 ve charges 3.11 Metallic Bonding Strong electrostatic forces of attraction between metal cations and delocalized mobile electrons Structure: lattice of +ve ions surrounded by mobile e-s Strength of metallic bond increases with: o Increasing positive charge on the ions in the lattice o Decreasing si

17、ze of metal ions in the lattice o Increasing number of mobile e-s per atom 3.12 Summary 4. STATES OF MATTER 4.1 Basic Assumptions of Kinetic Theory Ideal gas: a gas whose volume varies in proportion to temperature and in inverse proportion to pressure. Noble gases such as helium and neon approach id

18、eal behavior because of their low intermolecular forces. Ideal Gas Laws: Gas molecules move rapidly and randomly Distance between gas molecules is greater than diameter of molecules volume is negligible No forces of attraction/repulsion between molecules All collisions between particles are elastic

19、conserved Temperature of gas related to average of molecules Conditions at which gases behave ideally: o High temperature o Low pressure Limitations of Ideal Gas Laws: Real gases do not obey kinetic theory in two ways: o There is not zero attraction between molecules o We cannot ignore volume of mol

20、ecules themselves Deviations visible at low temp. and high pressure Molecules are close to each other Volume of molecules not negligible relative to container VDW forces present, pulling molecules to each other Pressure is lower than expected from ideal gas Effective volume is less than expected fro

21、m ideal gas 4.2 General Gas Equations = = 11 1 = 22 2 Quantity Unit Conversion Pressure Pascal 1 = 1000 Volume m3 13 = 10003 = 1106cm3 Temperature OK OC + 273 Standard Conditions: 101KPa and 273oK Mole Fraction = Partial Pressure of a Gas = 4.3 Liquid State Particles touching but may have gaps Have

22、to slide past each other in random motion Enthalpy of fusion: heat energy required to change 1 mole of solid into a liquid at its melting point no. of electron nuclear attraction Faster e- distortion Stronger force CIE AS LEVEL- CHEMISTRY 9701 Page 8 of 27 Heating a solid (melting): o Energy transfe

23、rred makes solid particles vibrate faster o Forces of attraction weaken vaporizes into purple gas o m.p./b.p. are slightly higher than room temp o Slightly soluble in water; dissolves in organic solvents o Diatomic molecule formed due to covalent bond between individual atoms o Molecules have weak V

24、an der Waals forces of attraction between them Temp. Ek Forces weaken More vapor CIE AS LEVEL- CHEMISTRY 9701 Page 9 of 27 Fullerenes: Buckminsterfullerenes(C60) Nanotubes C atoms in pentagonal and hexagonal rings C atoms in hexagonal rings only Spherical Cylindrical C60 molecules held together by V

25、DWs Structure is rod like due to continuing rings Conducts heat and electricity Very strong and tough Insoluble in water High m.p./b.p. 4.5 Ceramics Ceramic: an inorganic non-metallic solid prepared by heating one or a mixture of substance(s) to a high temp. Most ceramic are giant molecular structur

26、es Properties of ceramics: o High m.p./b.p. and hard strong covalent bonds o Dont conduct electricity/heat no mobile ions or e-s o Chemically unreactive e-s held in covalent bonds 4.6 Recycling Finite resource: resource which doesnt get replaced at the same rate that it is used up. Examples of finit

27、e resources: copper, aluminium, glass Advantage of Recycling: Saves energy Reduces environmental issues Conserves ore supplies Less wastage Cheaper than extracting 5. CHEMICAL ENERGETICS 5.1 Energy Change in Reactions Exothermic Reactions Endothermic Reactions Energy given out Surrounding warmer Bon

28、d making negative Energy taken in Surrounding cooler Bond breaking positive P4 Cl2 Ar 9.10 Electrical Conductivity Na Mg Al because no. of delocalized electrons which can carry charge increases Silicon is a semi-conductor Non-metals covalent no charge AlCl3 anhydrous - covalent; exists as dimer Al2C

29、l6 Hydrated - exists as ions; Al3+ and Cl- AlCl3(s) + H2O(l) Al2O3(s) + HCl(g) Al(OH)(H2O)52+ + HCl Oxi de + HC l(g) CIE AS LEVEL- CHEMISTRY 9701 Page 15 of 27 9.11 Electronegativity Increases across period because the bonded e- are in the same energy level but are attracted more strongly as no. of

30、protons increases 9.12 First Ionization Energy Generally increases as no. of protons increases Decrease Mg Al: more distant and less effective nuclear charge on 3p orbital Decrease P S: in S, one electron paired causing repulsion and easier to lose electron 10. GROUP II ALKALINE EARTH METALS m.p./b.

31、p. decreases down group: atoms/ions get larger, distance between nuclei alkanes = saturated hydrocarbons Non-polar no center of charge to act as either nucleophile or electrophile cannot attract polar reagents like acids, bases, metals or oxidizing agents Physical properties: The volatility of the a

32、lkanes decreases and m.p/b.p increases as number of carbon atoms increases Reason: increasing Van der Waals forces 14.2 Combustion Used as fuel because they burn in oxygen to given out large amounts of energy Alkanes kinetically stable in presence of O2; combustion occurs when necessary amount of Ea

33、 supplied Reaction occurs only in gas phase Complete: carbon dioxide + water Incomplete: carbon monoxide + carbon (soot) + water General Equation of Hydrocarbon Combustion: +( +4)2 2 +22 14.3 Substitution Alkanes react with halogens: 2 and 2 Example: Chlorination of Methane Reagent Condition Reactio

34、n Type Mechanism Cl2(g) UV light Substitution Free Radical CIE AS LEVEL- CHEMISTRY 9701 Page 21 of 27 Initiation: o Energy of a photon of light absorbed o bond breaks homolytically Propagation: o Highly reactive collides with a 4 molecule forming a new free radical; 3 4 + 3 + 3 +2 3 + o This can the

35、n react with another 2 and process repeats if sufficient 2 present until all are replaced Termination: o Reaction ends when 2 free radicals collide separated by fractional distillation Products and free radicals differ due to: o Halogen used: bromine requires more light o Alkane used: no. of C = var

36、iety of products 14.4 Cracking Breaking of large less useful alkanes into useful, more energy value smaller products using heat pi electrons loosely and more susceptible to attacks by e- deficient groups like electrophiles Alkenes combust completely carbon dioxide + water Give energy but not used as

37、 fuels; have other uses 14.7 Electrophilic Addition Mechanism Electrophile forms by heterolytic fission Electrophile attacks double bond Pair of e-s from double bond migrate to electrophile and bond breaks Carbocation formed which attacks the nucleophile 14.8 Carbocations Markovnikovs principle: an

38、electrophile adds to an unsymmetrical alkene so that the most stable carbocation is formed as an intermediate Hydrogen binds to carbon with more hydrogens Inductive effect of alkyl groups: o Alkyl groups donate e- to the ring o Producing a positive inductive effect o A larger alkyl group has a weake

39、r inductive effect 14.9 Addition Reactions Hy dro ge nat ion Alkene + H2 Alkane Reagent: H 2(g) Condition: o Catalyst: Nickel o Temp.: 100oC o Press.: 2 atm. Use: convert liquid oils to saturated solid fats Alkene + X2 Dihaloalkane Reagent: Halogen(aq) Condition: r.t.p./dark Alkene + Hydrohalogen Ha

40、logenoalkane Reagent: Hydrohalogen(g) Condition: r.t.p. Halo ge nat ion Hy dro - halo ge nat ion CIE AS LEVEL- CHEMISTRY 9701 Page 22 of 27 Alkene + H2O(g) Alcohol Reagent: steam Condition: o Catalyst: H3PO4 phosphoric acid o Temp.: 300oC o Press.: 70atm 14.10 Oxidation of Alkenes Both oxidation and

41、 addition to double bond involved KMnO4 changes from pink to colourless With Cold Dil. Acidified KMnO4/H+ Diol is formed With Hot Conc. Acidified KMnO4/H+ Leads to the rupture of the double bond Two compounds are formed Products formed depend on alkene 14.11 Polymerization Repeated addition of 1000s

42、 of alkene molecules (monomer) to each other forming a macromolecule Polyethene: o LDPE: cling wrap o HDPE: water pipes, wire insulation Polychloroethene (PVC): o Water pipes o Insulation of wires General conditions: high pressure, high temperature and catalyst Disadvantages: o Non-biodegradable: do

43、es not break down so increases amount of volume needed for landfill sites o Combustion produces harmful gases which contribute to global warming e.g. SO2, CO2 and HCl from PVCs Disposal of Polymers: o Recycle existing plastic o Make polymers biodegradable by adding starch units 15. HALOGEN DERIVATIV

44、ES 15.1 Types of Halogenoalkanes Primary 1o Secondary 2o Tertiary 3o SN2 SN1 15.2 Strength of C Hal Bond Polar Nature Bond Energy Reactivity Fluoro Decr ease Decr ease Increase s Chloro Bromo Iodo Electro-tivity decreases down group Bond length increases, bond energy decreases, lower EA so more reac

45、tive 15.3 Nucleophilic Substitution Mechanism The C X bond is a polar bond, has partial charges due to high electro-tivity of halogen. The + carbocation is easily susceptible to attack by a nucleophile SN1 Mechanism: Unimolecular only one molecule involved in 1st step Tertiary halogenoalkanes Hy dra

46、 tio n CIE AS LEVEL- CHEMISTRY 9701 Page 23 of 27 SN2 Mechanism: Bimolecular two molecules involved in 1st step Primary and secondary halogenoalkanes 15.4 Nucleophilic Substitution Reaction Hy dro lysis R X + OH- R OH + X- Reagent: strong alkali; NaOH(aq) or KOH(aq) Condition: heat/reflux Fluoroalka

47、nes are not hydrolysed because the C F bond is too strong Ease of hydrolysis increases: Primary Secondary Tertiary Tertiary halogenoalkanes can be hydrolysed without alkali Note: if any Cl- or Br- ions present in NaOH(aq), these ions will interfere with reaction Nitril e (c yan ide) R X + CN- RCN +

48、X- Reagent: KCN or NaCN in ethanol Condition: o Solvent: Ethanol o Heat/Reflux Reaction forms a C C bond therefore no. of C increases; name has one more carbon Prima ry Am ines R X + NH3 RNH2(l) + HX(g) Reagent: Ammonia (NH3) Condition: ammonia in alcohol under pressure in sealed container Note: if

49、excess conc. ammonia used, HX reacts with it forming NH4X 15.5 Reflux Many organic reactions proceed slowly Heating done under reflux to prevent volatile organic solvents to evaporate Mechanism similar to simple distillation 15.6 Elimination Reaction R X + OH- Alkene + X- + H2O Mechanism: Reagent: e

50、thanolic NaOH or KOH Conditions: temp. 60oC, reflux OH- acts as a proton acceptor; it accepts the H+ loss from the halogenoalkanes during elimination Elimination become progressively more easier Primary Secondary alkenes as they have hydrogen bonds Solubility of Alcohols in Water: Smaller alcohols m

51、ix completely with water since strong hydrogen bonds occur between alcohols and water As hydrocarbon nature increase (i.e. more C-C bonds), the non-polar character outweighs the ability of the OH to form hydrogen bonds and solubility decreases Small alcohols (e.g. ethanol) are good solvents for both

52、 polar and non-polar compounds as they have polar and non-polar components 16.3 Reaction with Sodium R OH + Na(l) RO- Na+ + H2(g) Type of reaction: acid-base Reagent used: liquid sodium metal Reactivity of alcohols decreases with increasing chain lengths of hydrocarbon Reaction less vigorous than th

53、at of Na and water which shows water is a stronger acid than alcohol 16.4 Reaction with Carboxylic Acids Reagent Condition Type of Reaction R-COOH Heat-reflux Conc. H 2SO4 Esterification Naming esters: Properties of Esters: Esters are volatile compounds no H-bonds so low m.p. Polar molecules soluble

54、 in organic solvents Sweet, fruity smelling liquids Many occur naturally e.g. as fats, oils are good solvents for polar ability to form hydrogen bonds decreases 17.1 Nucleophilic Addition with HCN Reagent Condition Type of Reaction HCN HCN w/alkali or HCN w/KCN Nucleophilic Addition Since HCN added,

55、 carbon chain increases Product formed is hydroxynitrile or cyanohydrine Aldehydes are more susceptible to nucleophilic attacks than ketones Smaller carbonyl compounds more reactive Product has a chiral carbon exhibits optical isomerism Mechanism: CIE AS LEVEL- CHEMISTRY 9701 Page 26 of 27 Note: HCN

56、 is a poor nucleophile and with few CN- ions, the reaction is slow. To increase CN- conc.: Make HCN react in presence of alkali HCN + OH- H2O + CN- Addition of KCN and dilute H2SO4 can provide HCN and more CN- ions 17.2 Reduction of Carbonyl Compounds Type of Reaction: nucleophilic addition (H- ions

57、) Reducing agents: o NaBH4 sodium tetrahydrioborate o LiAlH4 lithium aluminium hydride o H2/Pt or Ni Aldehydes 1o Alcohols Ketones 2o Alcohols R-CHO + 2H RCH2OH R-CO-R + 2H R-CH(OH)-R 17.3 Testing Carbonyl Compounds 2,4,- dinitrophenylhydrazine: It is a nucleophilic addition dont dissociate complete

58、ly Forms hydrogen bonds: o High m.p./b.p. o High solubility of smaller carboxylic acids Forms hydrogen bonded dimers when pure vapour, liquid or solid & when dissolved in non-polar organic solvents 18.1 Formation of Carboxylic Acids From alcohols: complete oxidation of primary alcohols From aldehyde

59、s: oxidation of aldehydes From nitriles: acid/base hydrolysis of a nitrile 18.2 Formation of Salts Heterolytic fission of the hydroxyl bond (-OH) Salts called carboxylates 19. ANALYTICAL TECHNIQUES 19.1 Infra-red Spectroscopy This is when a sample being analysed is irradiated with electromagnetic wa

60、ves in the infra-red region of the electromagnetic spectrum. Machine used is spectrophotometer and it detects intensity of wavelengths of infra-red that pass through the sample The energy absorbed corresponds to changes in vibration of bonds leading to the bond being to stretch, bend and twist CIE A

61、S LEVEL- CHEMISTRY 9701 Page 27 of 27 At a specific frequency, the resonance frequency, the largest vibrations are obtained Each type of vibration will absorb characteristic wavelengths of infra-red radiation We can hence identify the presence (or absence) of different functional groups from the abs

62、orbance pattern on an infra-red spectrum 19.2 Monitoring Air Pollution IR spectroscopy identifies particular bonds in a molecule, and so each pollutant will show a different pattern of absorptions this allows the identification of the pollution It is also possible to measure the concentration of each pollutant with the different amounts of absorption