化学专业英语《Chemistry English》课程教学资源（PPT课件）Lecture 08

Group 4 chemistry: key factsGroup 4 chemistry: key factsThe trend from non-metal to metal as the group is descended.4Non-metalsPhysicalproperties:brittle,insulatec(diamond)Chemical properties: CO, is acidic,siCCly is covalentGeMetalloids(准金属）metal/non-metalSnboundaryConduction changes withtemperature and impuritiesPbMetalsPhysicalproperties: ductile and malleable; conducts wellChemical properties: form cations Pb2+amphoteric oxides:--BasicityPbO(s) + 2H,O+(aq) → Pb2+(aq) + 3H,O(l)--AcidityPbO(s) + 2OH-(aq) + H,O(l) → Pb(OH)42-(aq)

1 Group 4 chemistry: key facts Group 4 chemistry: key facts The trend from non-metal to metal as the group is descended. 4 Non-metals Physical properties: brittle, insulate (diamond) Chemical properties:CO2 is acidic, CCl4 is covalent Metalloids(准金属) Conduction changes with temperature and impurities Metals Physical properties: ductile and malleable; conducts well Chemical properties: form cations Pb2+ amphoteric oxides: PbO(s) + 2H3O+ (aq) → Pb2+(aq) + 3H2O(l) -Basicity PbO(s) + 2OH- (aq) + H2O(l) → Pb(OH)4 2- (aq) -Acidity

Group 4 chemistry: key factsThe change in the most stable oxidation state from +IV to +ll asthe group is descendedElement+ll Oxidation state +IVCarbonmonoxide is reactive andcCCOCOburns easily to become carbondioxide. It is easily oxidized so is agood reductant, e.g. in the blastfurnace(高炉).SnSn2+→ Sn(OH)2- . Tin (II) is another reductant.e.g., SnCl,+ FeCl3(aq) →> SnCl4 + FeCl2Lead (IV) oxide is easily reducedPbPb2+PbO2to lead (II) ions so is a goodoxidant.PbO,(s) + 4HCl(aq) → PbCl(ag) + Cl(g) + 2H,O(I)2

2 Group 4 chemistry: key facts • Carbon monoxide is reactive and burns easily to become carbon dioxide. It is easily oxidized so is a good reductant, e.g. in the blast furnace(高炉). • Tin (II) is another reductant. • Lead (IV) oxide is easily reduced to lead (II) ions so is a good oxidant. The change in the most stable oxidation state from +IV to +II as the group is descended Element +II Oxidation state +IV C CO CO2 Sn Sn2+ Sn(OH)6 2- e.g., SnCl2+ FeCl3 (aq) → SnCl4 + FeCl2 Pb Pb2+ PbO2 PbO2 (s) + 4HCl(aq) → PbCl2 (aq) + Cl2 (g) + 2H2O(l)

Group4 chemistry:key factsThe unusual properties of the first member of the group1. Catenation Carbon forms strong bonds with itself and withhydrogen so there are millions of organic compounds2. Carbon forms strong π bonds with oxygen so the gas carbondioxide is molecular, while silicon forms relatively strongersigma bonds so the solid silicon dioxide is macromolecular.3. Tetrachloromethane is stable and not hydrolyzed, but all theother group 4 tetrachlorides are hydrolyzed3

3 Group 4 chemistry: key facts The unusual properties of the first member of the group 1. Catenation Carbon forms strong bonds with itself and with hydrogen so there are millions of organic compounds. 2. Carbon forms strong π bonds with oxygen so the gas carbon dioxide is molecular, while silicon forms relatively stronger sigma bonds so the solid silicon dioxide is macromolecular. 3. Tetrachloromethane is stable and not hydrolyzed, but all the other group 4 tetrachlorides are hydrolyzed

Group4chemistry:key ideasThe increase in atomic size as the group is descended leads to a lossof control over the outer electrons. Instead of electrons beinglocalized and held tightly in covalent bonds as they are at the top,they are delocalized and free to move in the metals. This trend is notclear cut, because graphite has delocalized electrons and conductslike a metal while below 13oC tin is most stable as a macromoleculargrey solid.The inert pair effect: the outer shell for group 4 is s?p?four outerelectrons available for bonding and so an oxidation state of +IV. But asthe group is descended the +IV oxidation state becomes less stablewith respect to the +II oxidation state. This trend is often called theinert pair effect because it appears that the two s electrons havebecome inert and less available for bonding leaving only the twoelectrons in the p orbitals able to take part in bonding .4

4 Group 4 chemistry: key ideas The increase in atomic size as the group is descended leads to a loss of control over the outer electrons. Instead of electrons being localized and held tightly in covalent bonds as they are at the top, they are delocalized and free to move in the metals. This trend is not clear cut, because graphite has delocalized electrons and conducts like a metal while below 13oC tin is most stable as a macromolecular grey solid. The inert pair effect: the outer shell for group 4 is s2p 2—four outer electrons available for bonding and so an oxidation state of +IV. But as the group is descended the +IV oxidation state becomes less stable with respect to the +II oxidation state. This trend is often called the inert pair effect because it appears that the two s electrons have become inert and less available for bonding leaving only the two electrons in the p orbitals able to take part in bonding

Group 4 chemistry: key ideas*Hybridizationandp-元overlapThe ground state for carbon is 1s?2s?2p?, which means that theouter shell electrons are of two kinds, s and p, and yet carbonforms four identical bonds. The ground state is only the lowestenergy state; an alternative state of higher energy has the fourouter electrons in sp3 hybrid orbitals which have some s andsome p character. These s-p hybrid orbitals can overlap betterthan s or p orbitals so producing stronger and identical bonds.O8Betteroverlap(round likes,twothanporbitalslobeslikep)porbitals-p hybridsorbital5

5 Group 4 chemistry: key ideas* Hybridization and p-πoverlap The ground state for carbon is 1s 22s 22p 2 , which means that the outer shell electrons are of two kinds, s and p, and yet carbon forms four identical bonds. The ground state is only the lowest energy state; an alternative state of higher energy has the four outer electrons in sp3 hybrid orbitals which have some s and some p character. These s-p hybrid orbitals can overlap better than s or p orbitals so producing stronger and identical bonds

Group 4 chemistry: key ideasElements in the second period of the periodic table have p orbitals ofthe same size as oxygen and so form strong pi bonds with oxygenSilicon in the third period has larger p orbitals which do not match insize and overlap well with oxygen's orbitals so strong pi bonds arenot formed.p orbitals of different sizep orbitals the same sizeproduce littleoverlapandproducegoodoverlapSweakbonds.andstrong元bonds.OO6

6 Group 4 chemistry: key ideas Elements in the second period of the periodic table have p orbitals of the same size as oxygen and so form strong pi bonds with oxygen. Silicon in the third period has larger p orbitals which do not match in size and overlap well with oxygen’s orbitals so strong pi bonds are not formed

Group 4 chemistry : key facts and ideasWordsWordsand ExpressionsCarbon; silicon; germanium; tin, leaddescendmetalloid: metalloidalcatenation: catenatehybridization; hybrid (hybrid orbitals); hybridizeoverlap7

7 Group 4 chemistry : key facts and ideas Words Carbon; silicon; germanium; tin, lead descend metalloid; metalloidal catenation; catenate hybridization; hybrid (hybrid orbitals); hybridize overlap Words and Expressions

Nitrogen chemistry: key factsNitrogen chemistry: key factsAMMONIAProperties due to the lone pair1. BaseNH,(g)+HCl(g) -NHCl(s) and NH,(g)+H,O(I)-NHt(aq)+OH(ag)2. Nucleophile2NH,(g) + CH,COCI(I) → CH,CONH2(s) +NH,Cl(s)3. Ligand4NH,(aq)+Cu2+(aq) → Cu(NH,)42+(aq)Redox propertiesNitrogen in ammonia has an oxidation state of-III and so can beoxidized to one of the many higher oxidation states of nitrogenAmmonia is therefore a reducing agent.8

8 Nitrogen chemistry: key facts Properties due to the lone pair 1. Base NH3 (g)+HCl(g) →NH4Cl(s) and NH3 (g)+H2O(l)→NH4 + (aq)+OH- (aq) 2. Nucleophile 2NH3 (g) + CH3COCl(l) → CH3CONH2 (s) +NH4Cl(s) 3. Ligand 4NH3 (aq)+Cu2+(aq) → Cu(NH3 ) 4 2+(aq) AMMONIA Redox properties Nitrogen in ammonia has an oxidation state of –III and so can be oxidized to one of the many higher oxidation states of nitrogen. Ammonia is therefore a reducing agent. Nitrogen chemistry: key facts

Nitrogen chemistry: key factsNITRICACIDAcidbasepropertiesNitric acid is a strong acidHNO,(I)+H,O(I) → H,O+(aq)+ NO,(aq) K, very largeRedox propertiesNitric acid contains nitrogen in the +V state and so it is readilyreduced. Nitric acid is therefore a strong oxidizing agent.9

9 Nitrogen chemistry: key facts Acid—base properties Nitric acid is a strong acid HNO3 (l)+H2O(l) → H3O+ (aq)+ NO3 - (aq) Ka very large NITRIC ACID Redox properties Nitric acid contains nitrogen in the +V state and so it is readily reduced. Nitric acid is therefore a strong oxidizing agent

Nitrogen chemistry: key facts*The manufacture of ammonia-theHaber processNitrogen and hydrogen are mixed in a l:3 mole ratio, heated,compressed, and passed over an iron catalyst. The reaction isexothermic, so the greatest equilibrium yield would be given by lowtemperature conditions. However, the rate is then too slow. At about500C20% of the reactants gases are converted to ammonia and theremainder recycled. It is important to remember that equilibrium isnever reached in the Haber process where new reactants areconstantly being added and ammonia is constantly being removedThe main uses of ammonia are for fertilizer production (80%),nylons, and nitric acid and explosivesN2(g)+3H(g) → 2NH,(g) △H= -92 kJ mol-1Temperature:500CPressure: between 200 and 1000 atmospheresCatalyst: Fe - a transition elementConversion: <20% at 200 atmospheres; ～50% at 1000 atmospheres10

10 Nitrogen chemistry: key facts* The manufacture of ammonia—the Haber process Nitrogen and hydrogen are mixed in a 1:3 mole ratio, heated, compressed, and passed over an iron catalyst. The reaction is exothermic, so the greatest equilibrium yield would be given by low temperature conditions. However, the rate is then too slow. At about 500oC 20% of the reactants gases are converted to ammonia and the remainder recycled. It is important to remember that equilibrium is never reached in the Haber process where new reactants are constantly being added and ammonia is constantly being removed. The main uses of ammonia are for fertilizer production (80%), nylons, and nitric acid and explosives. N2 (g)+3H2 (g) → 2NH3 (g) △H= -92 kJ mol-1 Temperature: 500oC Pressure: between 200 and 1000 atmospheres Catalyst: Fe – a transition element Conversion: <20% at 200 atmospheres; ～50% at 1000 atmospheres