Group 14

Element symbol Electron configuration Nature

Carbon C 2.4[He]2s22p2 Non- metal

Silicon Si 2.8.4[Ne]3s23p2

MetalloidGermanium Ge 2.8.18.4

[Ar]3d104s2 4p2

Tin Sn 2.8.18.18.4[Kr]4d105s2 5p2

MetalLead Pb 2.8.18.32.18.4

[Xe]4f14 5d106s2 6p2

All have four electrons in their valence shell with configuration : ns2np2

ns2 np2

Take note : group 14 : p block elementsthe similarity between elements in the same group

Variation in the physical properties

Atomic radiusFirst ionisation energyMelting pointElectrical conductivity

Atomic RadiusGroup 14 ( going down the group )Group 14 ( going down the group )

Nuclear charge & screening effect increases

But, increasing of screening effect LARGER than nuclear chargeWhy ? : Each electron has more one shell filled with e-

Thus, effective nuclear charge decreases

The attraction bet. Nucleus and electron become weaker

Atomic size increase

First Ionisation Energy1st ionisation energy dec , proton number inc

When atomic radius increase

Effective nuclear charge decrease

Easy to remove e-

C – Si : 1st ionisation energy decreases is big numberbig numberSi – Pb : Decrease more gradual

Why ? After Si ; the nuclear charge increase + the filling of the d d orbital and f f sub- orbital+ increase in atomic radius= effective nuclear charge dec more gradual

Element C Si Ge Sn Pb

1st ionisation energy/ KJ mol -1

1090 970 760 710 720

Question : why 1st Ionisation energy of Pb is HIGHER than Sn ?

Ans : Ineffective screening effect by the 4f electrons in Pb atom.Thus, a slight increase in the effective nuclear charge Sn to Pb

50Sn : [Kr] 4d105s25p2 ( Sn : 2.8.18.18.4 )

82Pb : [Kr] 4f145d106s26p2 ( Pb : 2.8.18.32.18.4 )

32 proton & electron screening effect does not

counter -balance the in nuclear chargebecause the shielding provided by the 4f electrons is less than expected

Melting point

Strength of covalent bond in lattice decrease : C > Si > Gesmallest size strong covalent bond

Sn and Pb - metal , form metallic bond ( solid )Hence, the melting point is lower than C, Si, GeMelting point of Pb > Sn = atoms of Pb are closely packed ( face centred cubic stucture )than atoms of Sn (tetragonal structure )

Also same trend in boiling points & enthalpy of vapourisation

Element C Si Ge Sn Pb

Melting point/oC 3730 1410 937 232 327

Structure Giant molecular(diamond-type) Giant metallic

Inc strength of metallic bond

Electrical conductivity going down the group

structure of elements changes ( covalent to giant metallic )= electrical cond. Increases

Carbon ( diamond ) a conductorSi & Ge ( metalloids ) semi –conductorsSn & Pb Good conductor (due to delocalised e- in metallic bonds )

Oxidation states of +2 and +4Elements have valence shell configuration of ns2 np2

Oxidation state of : +2 involves only p electrons : +4 involves both s and p electrons

? None of G14 forms simple M 4+ ions the ionisation energy is too high( +4 oxidation state of all element are covalent )*

For oxidation state of +2 : C , Si , Ge are covalent while Sn and Pb are ionic= due to in ionisation energy with proton number

Relative stability of the +2 and +4 oxidation state

The +4 oxidation state involves the promotion of an ss electron to an empty pp orbital.

Oxidation state +2 Oxidation state +4

If the energy is needed to promote s electron is compensated by the energy release when the covalent bonds are formed, element will show a stable covalency of 4 .

Energy absorbed

Going down the group Strength of covalent bonds formed with other element decreases

( due to inc in size )

Thus , the stability of the +4 oxidation state ,

tendency for G14 to show a valency of +2

•The behaviour of later members of G14 show a valency of less than 2 in the group valency through a failure to use their ss electrons and known as the inert pair effect

Relative stability :C , Si , Ge : +4 > +2 Sn : +4 > +2 Pb : +2 > +4

•When E0 value become inc positive ( down the group ),tendency for M4+ state get to convert to M 2+ state inc

C to Ge : +4 oxidation state is very stable compared to +2 ox. state

+2 oxidation state will change to +4 ox.state

= the +2 oxidation state are strong reducing agents ( electron donors )M2+ -> M4+ + 2 e-

In Sn : +4 oxidation state is slightly more stable than +2 ox.stateThus, tin ( 2) compounds are midly reducing.

In Pb : +2 oxidation state more stable than +4 ox.state.Pb (7) oxide is a strong oxisiding agent, Pb ( 2 ) oxide is stable

Formation of complex ions - All g14 ( EXCEPT C ) can make use of their empty orbitals to form complex

ions. - The central atoms make use of the empty d-orbitals to expand their

valency from 4 to 6- C cannot form complex ions -> no empty d-orbitals in valence shell. Thus,

the coordination number of C never excees 4

CatenationCatenation = ability of an element to form bonds bet. Atoms of the same

element.Carbon : ability to catenate to form stable long chain and ring compunds.

For catenation to occur :1.the bond must strong, M-M2.Similar in strength to those between M and other elements M-O

Element M-M M=M M M M-O

C 350 610 840 360

Si 222 - - 464

Ge 188 - - 360

Carbon ; smaller size ; strongest M-M bonds

C-C almost as strong as C-O

M-M bond for other element are weak

Carbon can form double and triple bonds bet. Carbon atoms.

Thus, only carbon can catenate to form a series of compounds known as “ organic atoms “

Remember !Silicon , Si – O bond is twice as strong as strong as Si- Si bond.Thus, silicon catenates can form SiO2 chain.

The allotropes of CarbonElement can exist in more than one form and exhibit allotropy is called allotropes.

DiamondoEach carbon atom undergoes sp3 hybridisation and bonded to four other carbon atom through strong covalent bonds strong covalent bonds ( tetrahedral arrangement )oRepeated three dimensional structureoHigh melting pointoAll the four valence electrons of C atom involves in the formation of covalent bonds - no free e- ( delocalised e- ) in solid structure.oThus, non- conductor of electricityoMetastable

GraphiteGraphite Example of a layered structure in the hexagonal crystalline system C atom undergoes sp2 hybridisation and covalently bonded to three other C atom to form hexagonal ringThe weak Van der Walls force allow the layer to slide over one another

Thus , it is soft and slipperyHigh melting point The more open structure of graphite as compared to diamond ; graphite less dense then diamondStable

Relative Stability of Graphite and DiamondMonotropy = all the allotropes can exist under a particular set of condition.

•Only one particular allotrope is more stable than the others.•No transition temperature

The transformation of diamond into graphites must be done by release heat energy.

Graphite is stable

Diamond is energetically unstableunstable but kinetically stable

Graphite is stable

Diamond is energetically unstableunstable but kinetically stable

Uses of Carbon Diamond -> use in the making of high speed drilling material & precious

stonesGraphite -> Used as lubricants, electrodes and moderator in nuclear reactorLead in pencilGraphite -> a component in the composite materials of bullet-proof vests &

in bodies of air crafts

TetrachloridesGroup 14 element exist as the simple MCl4 molecule with a tetrahedral shape( 109.5o)

Dry chlorine gas into liquid carbon disulphide boiling under refluxCatalyst : iodine / iron3Cl2 (g) + CS2 (l) CCl4 (l) + S2Cl2 (l)

Tetrachlorides of Si, Ge , Sn : react with chlorine gas and reflux

Pb tetrachoride : lead dioxide on cold and concentrated HCl ( < 5o) - to prevent the decomposition of lead tetrachloride

PbO2 ( s) + 4HCl (aq) PbCl4 (l) +2H2O (l)

Physical properties of tetrachlorides

The intermolecular force between tetrachloride molecules: weak van der Waals forces ( all in liquids )

( down the group )Size of molecules & total number of e- increases

Strength of van der Waals forces increases

Melting & boiling point increases

* CCl4 show abnormal behaviour

Thermal stability of the tetrachlorides( down the group )

Length of M-Cl bond increases( due to Inc size of elements & covalent bond gets weaker )

Thermal stability decreases

CCl4 , SiCl4 , GeCl4 are stable even at high temperaturesSnCl4 decomposes on strong heating to form tin (II) chloridePbCl4 decomposes on slight warming to give lead (II) choride

Oxides of Group 14Monoxides, MO ( oxidation state of +2)Dioxides, MO2 ( oxidation state of +4)

Thermal Stability of the monoxides CO2 – burn with a blue flame in air to produce dioxideSiO – only exists in gas phase at temperature above 20000c

When cooled, silicon dioxide and silicon are formed.GeO & SnO – oxidised to its dioxidesPbO > 4000c ( converted to triplumbum tetraoxide, Pb3O4 )

on continuous heating, triplumbum tetraoxide is converted back to lead monoxide.

* When heated with nitric acid,triplumbum tetraoxide form a colourless solution and brown soled of lead ( IV ) oxide is left.

Dioxides of G14 Dioxide CO2 SiO2 GeO2 SnO2 PbO2

Structure Simple molecule

Giant molecule

Intermediate between giant molecule and giant ionic

Physical state Gas Solid

Thermal stability

Stable even at high temperature Decomposes

Acid/ base nature

Acidic Amphoteric

React with acid

NaOH (to form carbonate)

Hot & con. NaOH( to form Silicate )

Hot & con. HCl( to form salts)

Hot & con. HCl( to form Lead ( II) chloride and Cl2 gas )

Alkali Hot and c. NaOH

Silicon Oxide Found in crystalline and amorphous form.

Quartz•Hard , brittle , clear and colourless

In solid state, each silicon atom is bonded covalently to 4 oxygen atom in tetrahedral mannerRatio Si to O2 is 1 :2 . Thus, empirical formula is SiO2

Quartz 870oc tridymite 1470 oc cristobalite

Uses of Silicon Oxide•Make glass and lenses for optical•Component in electronic devices•Make cement , concrete and ceramics•Extraction of phosphorus

GlassMelts at 1710 ocSoda lime glass : bottles , window panesPotash glass / hard glass : combustion tubes Borosilicate glass : make test tubes , laboratory glasswareAluminosilicate glass : cooking utensilsFibre Glass : car panels and aircraft componentsColoured glass : metallic oxides into the glass