Presentation on theme: "GROUP IV. General Characteristics C non-metal Si Ge Sn Pb All elements can form 4 covalent bonds in compounds. All elements form covalent hydrides (MH."— Presentation transcript:
General Characteristics C non-metal Si Ge Sn Pb All elements can form 4 covalent bonds in compounds. All elements form covalent hydrides (MH 4 ) and covalent chlorides (MCl 4 ). Carbon and silicon do not form ionic compound (except a few metal carbides containing C 4- ion). Going down the group, atomic size increase and can lose electron to form cations. Metalloids Metal
Physical properties of the elements. #briggs 270
Going 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 molecular Sn, Pb : Giant metallic M.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.
* Graph of M.P
Electrical 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. ElementsConductivityExplanation C diamond graphite poor good - no free electrons - all used for bonding. - one electron per carbon is not used for bonding and joins delocalised cloud. Sisemiconductor Gesemiconductor Sngoodmetallic bonding - delocalised electron cloud Pbgoodmetallic bonding - delocalised electron cloud
* Graph of electrical conductivity
Tetrachlorides All Group IV elements form chlorides with the formula XCl 4. 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
Thermal stability of tetrachlorides decrease down the group due to atomic radius of Group IV atom increase, weaker covalent bonds. CCl 4 is very stable to heat. PbCl 4 decompose slowly at room temperature to PbCl 2 and Cl 2 PbCl 4 PbCl 2 + Cl 2 yellow liquid white solidgas CCl 4, SiCl 4 and GeCl 4 are stable to heat, even at high temperature. SnCl 4 will decompose on strong heating.
Reaction of tetrachlorides with water. CCl 4 does not react with water – no empty orbitals to accept lone pair from oxygen of the water molecule. SiCl 4 hydrolysed in cold water to give an acidic solution: SiCl 4 + 2H 2 O 4HCl + SiO 2 white fumes GeCl 4 hydrolysed by water : GeCl 4 + 2H 2 O 4HCl + GeO 2 white fumes SnCl 4 and PbCl 4 are only partially hydrolysed by water.
Oxides 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 XO 2. 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.
C : +4 much more stable Si : +4 more stable Ge : +4 rather more stable Sn : +4 slightly more stable Pb : +2 much more stable. Stability of +4 over +2 oxidations state decrease.
E.g of reactions showing relative stabilities of oxides. 1) Oxidation of CO to CO 2. CO + ½ O 2 CO 2 H = very exothermic 2) PbO 2 decomposes on heating to form more stable PbO and O 2 gas. PbO 2 PbO + ½ O 2 3) PbCl 4 is thermally unstable PbCl 4 > PbCl 2 + Cl 2
E [Sn 4+ /Sn 2+ ] has a small positive value less tendency for Sn 4+ to be reduced to Sn 2+. Sn 4+ is more stable. E [Pb 4+ /Pb 2+ ] has a high positive value high tendency for Pb 4+ to be reduced to Pb 2+. Pb 2+ is more stable. PbO 2 is a powerful oxidising agent. * Refer to word document attachment for properties and reaction of Group IV oxides.*
Silicon(IV) oxide – SiO 2 Properties of silica bases ceramic: good electrical insulators good thermal insulators – high m.p and b.p. have great rigidity are hard – due to rigid tetrahedral arrangment. Uses : furnace linings glasses for solar panels power line insulators parts of turbines pottery porcelain