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