2General Characteristics C non-metalSiGeSnPbAll elements can form 4 covalent bonds in compounds.All elements form covalent hydrides (MH4) and covalent chlorides (MCl4).Carbon and silicon do not form ionic compound (except a few metal carbides containing C4- ion).Going down the group, atomic size increase and can lose electron to form cations.MetalloidsMetal
4Going down the group, atomic radius increase interatomic bonding becomes weaker attaraction of neighbouring nuclei for intervening electrons gets less.This results in change in bonding from covalent to metallic.Change in structure :C, Si, Ge : Giant molecularSn, Pb : Giant metallicM.p decreases from C to Ge – due to increase in atomic radius bond length increase weaker covalent bond.Hence the melting point and boiling point decreases going down the group.
6Electrical conductivity increases going down the group. This is due to increase of metallic character.Pure Si and Ge conduct electricity slightly. Conductivity can be increases by adding impurities semiconductors.ElementsConductivityExplanationC diamondgraphitepoorgood- no free electrons - all used for bonding.- one electron per carbon is not used for bonding and joins delocalised cloud.SisemiconductorGeSnmetallic bonding - delocalised electron cloudPb
8TetrachloridesAll Group IV elements form chlorides with the formula XCl4.Tetrachloride molecules are held together by weak Van der Waals forces.Low boiling point, liquid at room temperature.Going down the group, boiling point of the compound increase (volatility decrease) number of electrons increase, stronger Van der Waals forces.Shape : Tetrahedral
9yellow liquid white solid gas Thermal stability of tetrachlorides decrease down the group due to atomic radius of Group IV atom increase, weaker covalent bonds.CCl4 is very stable to heat.PbCl4 decompose slowly at room temperature to PbCl2 and Cl2PbCl PbCl Cl2yellow liquid white solid gasCCl4, SiCl4 and GeCl4 are stable to heat, even at high temperature.SnCl4 will decompose on strong heating.
10Reaction of tetrachlorides with water. CCl4 does not react with water – no empty orbitals to accept lone pair from oxygen of the water molecule.SiCl4 hydrolysed in cold water to give an acidic solution:SiCl H2O 4HCl + SiO2white fumesGeCl4 hydrolysed by water :GeCl H2O 4HCl + GeO2SnCl4 and PbCl4 are only partially hydrolysed by water.
11Oxides of Group IV elements Group IV can exist in two oxidation states to form oxides ( +2 and +4).Ground state :Excited state :Relative stability of higher and lower oxidation states of the elements.Going down the group, the oxidation +4 become less stable.From C to Sn, most stable oxide XO2.But Pb is most stable oxidation state +2. most stable oxide is PbO.This is due to ‘inert pair effect’ where the 2 outer s electrons remains relatively stable and unreactive.
12Ge : +4 rather more stable Sn : +4 slightly more stable C : +4 much more stableSi : +4 more stableGe : +4 rather more stableSn : +4 slightly more stablePb : +2 much more stable.Stability of +4 over +2 oxidations state decrease.
13E.g of reactions showing relative stabilities of oxides. 1) Oxidation of CO to CO2.CO + ½ O2 CO2 H = very exothermic2) PbO2 decomposes on heating to form more stable PbO and O2 gas.PbO2 PbO + ½ O23) PbCl4 is thermally unstablePbCl4 ——> PbCl2 + Cl2
14E [Sn4+/Sn2+] has a small positive value less tendency for Sn4+ to be reduced to Sn2+. Sn4+ is more stable.E [Pb4+/Pb2+] has a high positive value high tendency for Pb4+ to be reduced to Pb2+. Pb2+ is more stable.PbO2 is a powerful oxidising agent.* Refer to word document attachment for properties and reaction of Group IV oxides.*
15Silicon(IV) oxide – SiO2 Properties of silica bases ceramic:good electrical insulatorsgood thermal insulators – high m.p and b.p.have great rigidityare hard – due to rigid tetrahedral arrangment.Uses :furnace liningsglasses for solar panelspower line insulatorsparts of turbinespotteryporcelain