The P-block Elements(Summary)

8/10/2019 The P-block Elements(Summary)

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TTHHEE p p--BBLLOOCCK K EELLEEMMEE N NTTSS..

Group-15 elements.

N, P, As, Sb, BiGeneral characteristics:- El.confgn: ns2 np3 Extra stable due to half-filled p-confgn. Bcoz of the same reason, they have higher

ionisation enthalpies than gr-14 elements(Carbon family) There is a very small in size from As to Bi due to completely filled d- and f- orbitals in

heavier memebers (they have poor shielding effect)

PP hh yyssiiccaa ll pp rr oopp eerr tt iieess MMeettaalllliicc cchhaar r aacctteer r iinnccr r eeaasseess ddoowwnn tthhee ggr r oouu p p BBii iiss aa ssttr r oonngg mmeettaall dduuee ttoo hhiigghheer r II..EE.. b bccoozz oof f iittss ssmmaallll ssiizzee

EExxccee p ptt nniittr r ooggeenn,, aallll sshhooww aalllloottr r oo p pyy.. CC hh eemm iiccaa ll PP rr oopp eerr tt iieess

OOxxiiddaattiioonn ssttaatteess == --33,, ++33 aanndd ++55.. TThhee tteennddeennccyy ttoo sshhooww --33 ssttaattee ddeeccr r eeaasseess aass wwee ggoowwnn dduuee ttoo iinnccr r eeaassee iinn ssiizzee aanndd mmeettaalllliicc cchhaar r aacctteer r TThhee ssttaa b biilliittyy oof f ++33 ssttaattee iinnccr r eeaasseess ddoowwnn tthhee ggr r oouu p p wwhheer r eeaass tthhaatt oof f ++55 ssttaattee ddeeccr r eeaasseess dduuee ttoo II N NEER R TT--PPAAIIR R eef f f f eecctt BBii sshhoowwss ++55 oonnllyy wwiitthh f f lluuoor r iinnee ((BBiiFF55)) dduuee ttoo hhiigghh p poollaar r iizziinngg p poowweer r oof f f f lluuoor r iinnee..

Conseqences of inert-pair effect Nitrogen compounds disproportionate in acid solutions.

3HNO2 HNO3 + H2O + 2NO Similarly, in case of phosphorus nearly all intermediate oxidation states disproportionate

into +5 and 3 both in alkali and acid. But the +3 oxidation state in case of arsenic, antimony and bismuth becomes increasingly

stable and do not ungergo disproportionation.Anomalous properties of Nitrogen

It can show a maximum covalency of four only whereas others show 5 and 6. forerxample:-PCl5 and PF6-

This is due to the absence of vacant d-orbitals in N-atom It forms strong p-p multiple bonds due to its small size. This is why it exists as a

diatomic molecule with a triple bond between two N-atoms.Others do not form such bonds bcoz their atomic orbitals are so large and diffused that theycan not have effective overlapping.


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R R eeaaccttiivviittyy ttoowwaar r ddss mmeettaallss

AAllll tthheessee eelleemmeennttss r r eeaacctt wwiitthh mmeettaallss ttoo f f oor r mm tthheeiir r b biinnaar r yy ccoomm p poouunnddss eexxhhii b biittiinngg 33 ooxxiiddaattiioonn ssttaattee

CCaa33 N N

22 ((ccaallcciiuumm nniittr r iiddee)) CCaa

33PP

22 ((ccaallcciiuumm p phhooss p phhiiddee)),,

?????? QQUUEESSTTIIOO N N ?????? 11..PPHH33 hhaass lloowweer r b booiilliinngg p pooiinntt tthhaann N NHH33.. WWhhyy??

UUnnlliik k ee N NHH33,, PPHH33 mmoolleeccuulleess ddoo nnoott f f oor r mm iinntteer r mmoolleeccuullaar r hhyyddr r ooggeenn b boonnddiinngg iinn lliiq q uuiidd ssttaattee.. TThhaatt iiss wwhhyy tthhee b booiilliinngg p pooiinntt oof f PPHH33 iiss lloowweer r tthhaann N NHH33..

22.. N NHH33 iiss ssoolluu b bee iinn wwaatteer r wwhheer r eeaass PPHH33 iiss iinnssoolluu b bllee..WWhhyy??

DINITROGEN (N2)

PROPERTIES OF N2 * At higher temperatures, it directly combines with some metals to form predominantly ionic

nitrides and with non-metals, covalent nitrides.6Li + N2 2Li3 N3Mg + N2 Mg3 N2

* Dinitrogen combines with dioxygen only at very high temperature (at about 2000 K) toform nitric oxide, NO. N2 + O2(g) 2NO(g)

UUSSEE SS OO FF NN22 iinn tthhee mmaannuuf f aaccttuur r ee oof f aammmmoonniiaa iinn tthhee mmaannuuf f aaccttuur r ee oof f cchheemmiiccaallss ccoonnttaaiinniinngg nniittr r ooggeenn,, ((ee..gg..,, ccaallcciiuumm ccyyaannaammiiddee)).. IItt aallssoo f f iinnddss uussee wwhheer r ee aann iinneer r tt aattmmooss p phheer r ee iiss r r eeq q uuiir r eedd ((ee..gg..,, iinn iir r oonn aanndd sstteeeell iinndduussttr r yy,, iinneer r tt

ddiilluueenntt f f oor r r r eeaaccttiivvee cchheemmiiccaallss)).. LLiiq q uuiidd ddiinniittr r ooggeenn iiss uusseedd aass aa r r eef f r r iiggeer r aanntt ttoo p pr r eesseer r vvee b biioollooggiiccaall mmaatteer r iiaallss,, f f oooodd iitteemmss aanndd

iinn ccr r yyoossuur r ggeer r yy..

EE vvaa lluu aa tt iioonn QQ uu eesstt iioonn ss

QQ.. WWr r iittee tthhee r r eeaaccttiioonn oof f tthheer r mmaall ddeeccoomm p poossiittiioonn oof f ssooddiiuumm aazziiddee.. AAnnss::--TThheer r mmaall ddeeccoomm p poossiittiioonn oof f ssooddiiuumm aazziiddee ggiivveess ddiinniittr r ooggeenn ggaass.. 22 N Naa N N33 22 N Naa ++ 33 N N22

QQ.. WWhhyy iiss N N22 lleessss r r eeaaccttiivvee aatt r r oooomm tteemm p peeaar r aattuur r ee??

AAMMMMOO N NIIAA OOnn aa ssmmaallll ssccaallee aammmmoonniiaa iiss oo b bttaaiinneedd f f r r oomm aammmmoonniiuumm ssaallttss wwhhiicchh ddeeccoomm p poossee wwhheenn

ttr r eeaatteedd wwiitthh ccaauussttiicc ssooddaa oor r lliimmee..


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22 N NHH44CCll ++ CCaa((OOHH))22 22 N NHH33 ++ 22HH22OO ++ CCaaCCll22 (( N NHH44))22 SSOO44 ++ 22 N NaaOOHH 22 N NHH33 ++ 22HH22OO ++ N Naa22SSOO44

OOnn aa llaar r ggee ssccaallee,, aammmmoonniiaa iiss mmaannuuf f aaccttuur r eedd b byy HHaa b beer r ss p pr r oocceessss.. N N22((gg)) ++ 33HH22((gg)) 22 N NHH33((gg));; EEnntthhaall p pyy cchhaannggee == 4466..11 k k JJ mmooll 11 CCoonnddiittiioonnss f f oor r b beetttteer r yyiieelldd aar r ee::--

IInn aaccccoor r ddaannccee wwiitthh LLee CChhaatteelliieer r ss p pr r iinnccii p pllee,, hhiigghh p pr r eessssuur r ee wwoouulldd f f aavvoouur r tthhee f f oor r mmaattiioonn oof f aammmmoonniiaa.. TThhee oo p pttiimmuumm ccoonnddiittiioonnss f f oor r tthhee p pr r oodduuccttiioonn oof f aammmmoonniiaa aar r ee aa p pr r eessssuur r ee oof f 220000 aattmm,, aa

tteemm p peer r aattuur r ee oof f ~~ 770000 K K aanndd tthhee uussee oof f aa ccaattaallyysstt ssuucchh aass iir r oonn ooxxiiddee wwiitthh ssmmaallll aammoouunnttss oof f K K 22OO aanndd AAll22OO33 ttoo iinnccr r eeaassee tthhee r r aattee oof f aattttaaiinnmmeenntt oof f eeq q uuiillii b br r iiuumm..

Structure of ammoniaThe ammonia molecule is trigonal pyramidal with the nitrogen atom at the apex. It has three bond pairs and one lone pair of electrons as shown in the structure.

Properties of ammonia

* Ammonia gas is highly soluble in water as it forms intermolecular H-bonds with watermolecules.

* It is a Lewis base as it can donate the lone pair present on the N-atom.* It donates the electron pair forming linkages with metal ions and therefore form complex

compounds.This finds applications in detection of metal ionssuch as Cu2+, Ag+:

Cu2+ (aq) + 4 NH3(aq) [Cu(NH3)4]2+(aq)Deep blue

AgCl(s) + 2NH3(aq) [Ag(NH3)2]Cl(aq)White ppt Excess Soluble


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OXIDES OF NITROGEN Oxides of Nitrogen possess planar structure due to the ability of N to form multiple bonds.

(Oxides of P have cage like structures since P can not form strong multiple bonds)

STRUCTURE-


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Evaluation Questions What is the covalence of N in (a)N2O5 and (b) N2O4? Why does NO2 dimerize? Can NO dimerize? Why is the precipitate of AgCl soluble in excess of ammonia? Why is ammonia a Lewis base?

NITRIC ACIDLarge Scale Manufacure:-Ostwald process .

Based on catalytic oxidation of ammonia.Pt /Rh

4NH3 g + 5O2 g 4NO g + 6H2 O g(from air) 500K; 9 bar

Nitric oxide thus formed combines with oxygen giving NO2.2NO g + O2 g 2NO2 g Nitrogen dioxide so formed, dissolves in water to give HNO3.

3NO2 g + H2 O 2HNO3 aq + NO g NO thus formed is recycled and the aqueous HNO3 can be concentrated by distillation upto~ 68% by mass. Further concentration to 98% can be achieved by dehydration with

concentrated H2SO4.


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Lab. Preparation of Nitric acid:- In lab, nitric acid is prepared by heating potassium nitrate or sodium nitrate with conc.

sulphuric acid in a glass resort. NaNO3 + H2SO4 NaHSO4 + HNO3

Shape of Nitric acid molecule In the gaseous state, HNO3 exists as a planar molecule with the structure as shown.

H O

O N

OProperties of Nitric acid

In aqueous solution, nitric acid behaves as a strong acid giving hydronium and nitrate ions.HNO3(aq) + H2O(l) H3O+(aq) + NO3

-(aq) Concentrated nitric acid is a strong oxidising agent and attacks most metals except noble

metals such as gold and platinum. The products of oxidation depend upon the concentrationof the acid, temperature and the nature of the material undergoing oxidation.3Cu + 8 HNO3(dilute) 3Cu(NO3)2 + 2NO + 4H2OCu + 4HNO3(conc.) Cu(NO3)2 + 2NO2 + 2H2O

Zinc reacts with dilute nitric acid to give N2O and with concentrated acid to give NO2.4Zn + 10HNO3(dilute) 4 Zn (NO3)2 + 5H2O + N2OZn + 4HNO3(conc.) Zn (NO3)2 + 2H2O + 2NO2

Some metals (e.g., Cr, Al) do not dissolve in concentrated nitric acid because of theformation of a passive film of oxide on the surface.

Concentrated nitric acid also oxidises nonmetals and their compounds. Iodine is oxidisedto iodic acid, carbon to carbon dioxide, sulphur to H2SO4, and phosphorus to phosphoricacid.

Properties of nitric acid-Contd.. Concentrated nitric acid also oxidises nonmetals and their compounds. Iodine is oxidised

to iodic acid, carbon to carbon dioxide, sulphur to H2SO4, and phosphorus to phosphoricacid.

I2 +10HNO3 2HIO3 + 10 NO2 + H2O

C + 4HNO3 CO2 + 2H2O + 4NO2 S8 + 48HNO3(conc.) 8H2SO4 +48NO2 + 16H2OP4 + 20HNO3(conc.) 4H3PO4 +20 NO2 + 4H2O

Chemistry of Brown ring test:-


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Brown Ring Test : The brown ring test for nitrates depends on the ability of Fe2+ to reduce nitratesto nitric oxide, which reacts with Fe2+ to form a brown coloured complex.

The test is usually carried out by adding dilute ferrous sulphate solution to an aqueoussolution containing nitrate ion, and then carefully adding concentrated sulphuric acid alongthe sides of the test tube. A brown ring at the interface between the solution and sulphuric

acid layers indicate the presence of nitrate ion in the solution. NO3 - + 3Fe2+ + 4H+ NO + 3Fe3+ + 2H2O

[Fe(H2O)6]2+ + NO [Fe (H2O)5 (NO)]2+ + H2O(brown)

Uses of Nitric acid In the mfr. of ammonium nitrate for fertilizer. In the mfr. of nitrates required for making explosives and pyrotechnics. In making TNT, nitroglycerin In pickling of stainless steel, etching of glass As oxidizer in rocket fuels.

PHOSPHOROUS.

White Phosphorous :-

P4 +3NaOH + 3H2O PH3 + 3NaH2 PO2

sodium hypophosphite

Reaction with Oxygen:- P4 + 5O2 P4O10

S.No White Phosphorous Red Phosphorous

1 Poisonous Non-poisonous

2 Soluble in CS2 Insoluble in CS2

3 Glows in dark Doesnt


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Structure:- It consists of discrete P4 tetrahedron units.

Red Phosphorous:-

Red phosphorus is obtained by heating white phosphorus at 573K in an inert atmosphere for

several days.Structure:- It has a chain-like structure.

Black phosphorous has two forms alpha-black phosphorous and beta-black phosphorous.

PHOSPHINE:- (PH 3)

Preparation:-

1.Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.

Ca3P2 + 6H2O 3Ca(OH)2 + 2PH3

Ca3P2 + 6HCl 3CaCl2 + 2PH3

2.In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solutionin an inert atmosphere of CO2.

P4 +3NaOH + 3H2O PH3 + 3NaH2 PO2

sodium hypophosphite


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When pure, it is non inflammable but becomes inflammable owing to the presence ofP2H4 or P4 vapours. To purify it from the impurities, it is absorbed in HI to form phosphoniumiodide (PH4I) which on treating with KOH gives off phosphine.

PH4 I + KOH KI + H2O + PH3

Properties:-

1. 3CuSO4 + 2PH3 Cu3P2 + 3H2SO4

2. 3HgCl2 + 2PH3 Hg3P2 + 6HCl

3. Phosphine is weakly basic and like ammonia, gives phosphonium compounds with acidse.g., PH3 + HBr PH4 Br

Uses of Phopsphine:- The spontaneous combustion of phosphine is technically used in Holmes signals .

Containers containing calcium carbide and calcium phosphide are pierced and thrownin the sea when the gases evolved burn and serve as a signal.

It is also used in smoke screens .

Halides of Phosphorous:-

1. PCl3:-

Preparation:-P4 + Cl2 PCl3

P4 + 8SOCl2 4PCl3 + + 4SO2 + 2S2Cl2

Properties:-

(i)It fumes in moist air due to the formation of HCl.

PCl3 + 3H2O H3PO3 + 3HCl

(ii)It reacts with organic compounds containing OH group such as CH3COOH, C2H5OH.

3CH3COOH + PCl3 3CH3COCl +H3PO3

3C2H5OH+ PCl3 3C2H5Cl + H3PO3


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Structure:_

It has a pyramidal shape as shown, in which phosphorus issp3 hybridised.

Phosphorous Trichloride

ll

l

P

..Lone pair

2.PCl 5:-

Preparation:-

(i)Phosphorus pentachloride is prepared by the reaction of white phosphorus with excessof dry chlorine.

P4 + 10Cl2 4PCl5

(ii)It can also be prepared by the action of SO2Cl2 on phosphorus.

P4 + 10SO2Cl2 4PCl5 + 10SO2

Properties:-

(i)In moist air, it hydrolyses to POCl3 and finally gets converted to phosphoric acid.

PCl5 + H2O POCl3 + 2HCl

POCl3 + 3H2O H3PO4 + 3HCl

(ii)When heated, it sublimes but decomposes on stronger heating.

PCl5 PCl3 + Cl2

(iii)It reacts with organic compounds containing OH group converting them to chloroderivatives.

3CH3COOH + PCl5 3CH3COCl +POCl3 + HCl


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3C2H5OH+ PCl5 3C2H5Cl + POCl3 + HCl

(iv)Finely divided metals on heating with PCl5 give corresponding chlorides.

2Ag + PCl5 2AgCl + PCl3

Sn + 2PCl5 SnCl4 + 2PCl3

(v) In the solid state it exists as an ionic solid, [PCl4]+[PCl6] in which the cation, [PCl4]+ istetrahedral and the anion, [PCl6] octahedral.

Structure:- Trigonal bipyramidal

The three equatorial PCl bonds are equivalent, while the two axial bonds are longer thanequatorial bonds. This is due to the fact that the axial bond pairs suffer more repulsion ascompared to equatorial bond pairs.

Uses:-

It is used in the synthesis of some organic compounds, e.g., C2H5Cl, CH3COCl.


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OXOACIDS OF PHOSPHOROUS:-


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(i)The acids in +3 oxidation state of phosphorus tend to disproportionate to higher and loweroxidation states. For example, orthophophorous acid (or phosphorous acid) on heatingdisproportionates to give orthophosphoric acid (or phosphoric acid) and phosphine.

4H3PO3 3H3PO4 + PH3

(ii)The acids which contain PH bond have strong reducing properties.Thus, hypophosphorousacid is a good reducing agent as it contains two PH bonds and reduces, for example, AgNO3 tometallic silver.

4 AgNO3 + 2H2O + H3PO2 4Ag + 4HNO 3 + H3PO4

Group 16 Elements

1.They havens2np 4 general electronic configuration.

2.The elements of this group have lower ionisation enthalpy values compared to those ofGroup15 in the corresponding periods.

This is due to the fact that Group 15 elements have extra stable half-filled p orbitalelectronic configurations.

3.Because of the compact nature of oxygen atom, it has less negative electron gain enthalpy thansulphur.

4.Next to fluorine, oxygen has the highest electronegativity value amongst the elements.

5.Oxygen and sulphur are non-metals, selenium and tellurium metalloids, whereas polonium is ametal.Polonium is radioactive and is short lived (Half-life 13.8 days).

6.The large difference between the melting and boiling points of oxygen and sulphur may beexplained on the basis of their atomicity; oxygen exists as diatomic molecule (O2) whereassulphur exists as polyatomic molecule (S8).

Oxidation states and trends in chemical reactivity:-

1. Since electronegativity of oxygen is very high, it shows only negative oxidation state as 2except in the case of OF2 where its oxidation state is + 2

2.The stability of + 6 oxidation state decreases down the group and stability of + 4 oxidationstate increase (inert pair effect)

Anomalous behaviour of oxygen:-

1.The anomalous behaviour of oxygen, like other members of p-block


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present in second period is due to its small size and high electronegativity. One typical exampleof effects of small size and high electronegativity is the presence of strong hydrogen bonding inH2O which is not found in H2S.

2.The absence ofd orbitals in oxygen limits its covalency to four and in practice, rarely exceeds

two. On the other hand, in case of other elements of the group, the valence shells can be xpandedand covalence exceeds four.

Reactivity with hydrogen :

All the elements of Group 16 form hydrides of the type H2E (E =O, S, Se, Te, Po) H2O H2S H2Se H2Te

BDE Decreases

Stability decreases

Acidity increasesReducing nature increases

Reactivity with oxygen :

All these elements form oxides of the EO2 and EO3 types where E = S, Se, Te or Po. Ozone (O

3) and sulphur dioxide (SO

2) are gases while selenium dioxide (SeO

2) is solid.

Reducing property of dioxide decreases from SO2 to TeO2; SO2 is reducing while TeO2 isan oxidising agent

Both types of oxides are acidic in nature.

Reactivity towards the halogens .

The stability of the halides decreases in the order F > Cl > Br > I . Amongst hexahalides, hexafluorides are the only stable halides. They have octahedral structure. Sulphurhexafluoride, SF6 is exceptionally stable for steric reasons.

Tetrafluorides, havesp3d hybridisation and thus, have trigonal bipyramidal structures inwhich one of the equatorial positions is occupied by a lone pair of electrons. Thisgeometry is also regarded assee-saw geometry.


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Dihalides have sp 3 hybridisation and thus, have tetrahedral structure. The well known monohalides are dimeric in nature. Examples are S2F2, S2Cl2, S2Br 2,

Se2Cl2 and Se2Br 2. These dimeric halides undergo disproportionation as given below:

2Se2Cl2 SeCl4 + 3Se

Question:-

1.H2S is less acidic than H2Te. Why?

Due to the decrease in bond (EH) dissociation enthalpy down the group, acidic characterincreases.

2. Why is H2O a liquid and H2S a gas ?

DIOXYGEN

Dioxygen can be obtained in the laboratory by the following ways:

(i) By heating oxygen containing salts such as chlorates, nitrates and permanganates.

2KClO3 2 KCl + 3 O2

MnO2

(ii) By the thermal decomposition of the oxides of metals low in the electrochemical series andhigher oxides of some metals.

2Ag2O(s) 4Ag(s) + O2(g);

2Pb3O4(s) 6PbO(s) + O2(g)

2HgO(s) 2Hg(l) + O2(g) ;

2PbO2(s) 2PbO(s) + O2(g)

(iii) Hydrogen peroxide is readily decomposed into water and dioxygen by catalysts such asfinely divided metals and manganese dioxide.


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2H2O2(aq) 2H2O(1) + O2(g)

(iv) On large scale it can be prepared from water or air. Electrolysis of water leads to the releaseof hydrogen at the cathode and oxygen at the anode.

Properties1.Molecular oxygen, O2 is unique in being paramagnetic inspite of having even number ofelectrons .

2.Its combination with other elements is often strongly exothermic which helps in sustaining thereaction. However, to initiate the reaction, some external heating is required as bond dissociationenthalpy of oxgyen-oxygendouble bond is high (493.4 kJ mol1).

2.Some compounds are catalytically oxidised. For e.g.,

2SO2 + O2 2SO3

5HCl + O2 2Cl2 + 2H2O

CuCl2

Uses Of Dioxygen:- Self work

Oxides:-

A binary compound of oxygen with another element is called oxide.

Oxides can be simple (e.g., MgO, Al2O3 ) or mixed (Pb3O4, Fe3O4).

Acidic or Basic or Amphoteric or Neutral

Reactions to show that aluminium oxide is amphoteric:-Al2O3+ 6HCl+ 9H2O 2[Al(H2O)6]Cl3 (aq)

Al2O3+ 6NaOH +3H2O Na3[Al(OH)6] (aq)

OZONE:-


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Ozone is an allotropic form of oxygen. It is too reactive to remain for long in the atmosphere atsea level. At a height of about 20 kilometres, it is formed from atmospheric oxygen in the presence of sunlight. This ozone layer protects the earths surface from an excessiveconcentration of ultraviolet (UV) radiations.

Preparation:- When a slow dry stream of oxygen is passed through a silent electrical discharge,conversion of oxygen to ozone (10%) occurs. The product is known as ozonised oxygen.

3O2 2O3 H = +ve

Since the formation of ozone from oxygen is an endothermic process, it is necessary to use asilent electrical discharge in its preparation to prevent its decomposition.

PROPERTIES OF OZONE:-

1.Ozone is thermodynamically unstable with respect to oxygen since its decomposition intooxygen results in the liberation of heat (H is negative) and an increase in entropy (S is positive). These two effects reinforce each other, resulting in large negative Gibbs energy change(G) for its conversion into oxygen.

2.Due to the ease with which it liberates atoms of nascent oxygen(O3 O2 + [O] ), it acts as a powerful oxidising agent.

For e.g., it oxidizes lead sulphide to lead sulphate and iodide ions to iodine.PbS(s) + 4O3(g) PbSO4(s) + 4O2(g)

2I (aq) + H2O(l) + O3(g) 2OH (aq) + I2(s) + O2(g)

3. Estimation of ozone :-When ozone reacts with an excess of potassium iodide solution bufferedwith a borate buffer (pH 9.2), iodine is liberated which can be titrated against a standard solutionof sodium thiosulphate. This is a quantitative method for estimating O3 gas.

4.Nitrogen oxides (particularly nitric oxide) combine very rapidly with ozone and there is, thus,

the possibility that nitrogen oxides emitted from the exhaust systems of supersonic jetaeroplanes might be slowly depleting the concentration of the ozone layer in the upperatmosphere.

NO + O3 NO2 + O2

Structure of Ozone :- Angular .


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Uses of Ozone : It is used as a germicide, disinfectant and for sterilising water. It is also used for

bleaching oils, ivory, flour, starch, etc. It acts as an oxidising agent in the manufacture of potassium permanganate.

SULPHUR

Yellow rhombic sulphur = Monoclinic sulphur

Transition temp = 369 K

Both rhombic and monoclinic sulphur have S8 molecules.

At elevated temperatures (~1000 K), S 2 is the dominant species and is paramagnetic like O 2


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In vapour state sulphur partly exists as S 2 molecule which has two unpaired electrons in theantibonding * orbitals like O 2 and, hence, exhibits paramagnetism .

Preparation:-1.Sulphur dioxide is formed together with a little (6-8%) sulphur trioxide when sulphur is burntin air or oxygen:

S(s) + O2(g) SO2 (g)

2.In the laboratory it is readily generated by treating a sulphite with dilute sulphuric acid.

SO3 2- + 2H+(aq ) H2O(l) + SO2 (g)

Properties:-

1.2NaOH + SO2 Na2SO3 + H2O

Na2SO3 + H2O + SO2 2NaHSO3

(Excess)

SO2(g) + Cl2 (g) SO2Cl2(l)

Charcoal

2. When moist, sulphur dioxide behaves as a reducing agent.

For example,

1.it converts iron(III) ions to iron(II) ions

2Fe3+ + SO2 + 2H2O 2Fe2+ + SO42- + 4H+

2. it decolourises acidified potassium permanganate(VII) solution;this reaction is aconvenient test for the gas.

5SO2 + 2MnO4-+2H2O 5SO42- + 4H+ + 2Mn2+

Structure:- The molecule of SO2 is angular. It is a resonance hybrid of the two canonical forms:


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Uses:- Sulphur dioxide is used (i) in refining petroleum and sugar (ii) in bleaching wool and silkand (iii) as an anti-chlor, disinfectant and preservative. Sulphuric acid, sodium hydrogen sulphiteand calcium hydrogen sulphite (industrial chemicals) are manufactured from sulphur dioxide.

Liquid SO2 is used as a solvent to dissolve a number of organic and inorganic chemicals.

Oxoacids of Sulphur

SULPHURIC ACID:-

Sulphuric acid is manufactured by theContact Process which involves three steps:

(i) burning of sulphur or sulphide ores in air to generate SO2.

S+ O2 SO2

(ii) conversion of SO2 to SO3 by the reaction with oxygen in the presence of a catalyst (V2O5)

2SO2 + O2 2SO3

(iii) absorption of SO3 in H2SO4 to giveOleum (H2S2O7).


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SO3 + H2SO4 H2S2O7

H2S2O7 + H2O 2 H2SO4

The favourable conditions for maximum yield are a pressure of 2 bar and a temperature of 720K.

PROPERTIES OF SULPHURIC ACID:-

1.It dissolves in water with the evolution of a large quantity of heat. Hence, care must be takenwhile preparing sulphuric acid solution from concentrated sulphuric acid. The concentrated acidmust be added slowly into water with constant stirring.

2.The chemical reactions of sulphuric acid are as a result of the following characteristics: (a) lowvolatility (b) strong acidic character (c) strong affinity for water and (d) ability to act as anoxidising agent.

3. In aqueous solution, sulphuric acid ionises in two steps.

H2SO4 + H2O H3O+ + HSO4- ( Ka1 = very large )

HSO4- + H2O H3O+ + SO42- ( Ka 2 = very low)

The larger value of Ka1 means that H2SO4 is largely dissociated into H+ and HSO4- ions. Greater the value of dissociation constant (K a), the stronger is the acid.

4.. 2 MX + H2SO4 2 HX + M2SO4 (X = F, Cl, NO3)

(M = Metal)

5. Concentrated sulphuric acid is a strong dehydrating agent.

C12H22O11 12C + 11H2O

c-H2SO4

6.Hot concentrated sulphuric acid is a moderately strong oxidizing agent.

Cu + 2 H2SO4(conc.) CuSO4 + SO2 + 2H2O

3S + 2H2SO4(conc.) 3SO2 + 2H2O

C + 2H2SO4(conc.) CO2 + 2 SO2 + 2 H2O

Uses :-


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In the manufacture of fertilizers (e.g., ammonium sulphate, superphosphate). petroleum refining ,manufacture of pigments, paints and dyestuff intermediates , detergent industry , metallurgicalapplications (e.g.,cleansing metals before enameling, electroplating and galvanising, storage batteries , in the manufacture of nitrocellulose products and, as a laboratory reagent.

QUESTIONS:-What happens when

(i) Concentrated H2SO4 is added to calcium fluoride

(ii) SO3 is passed through water?

Answer:-

(i) It forms hydrogen fluoride

CaF2 + H2 SO4 CaSO4 + 2HF

(ii) It dissolves SO3 to give H2SO4 .

SO3 + H2O H2 SO4

GROUP 17 ELENTS- HALOGENS .

1. Outermost confioguration isns2np5.

2. They have very high ionization enthalpy due to very small atomic size. The I.E. decreases aswe go down the group.

3.They have maximum negative electron gain enthalpy in the corresponding periods .This is bcoz after gaining an electron they attain the stable noble gas configuration.

However, thenegative electron gain enthalpy of fluorine is less than that of chlorine. It is due tosmall size of fluorine atom. As a result, there are strong interelectronic repulsions in therelatively small 2 p orbitals of fluorine and thus, the incoming electron does not experience muchattraction.

4. All halogens arecoloured. This is due to absorption of radiations in visible region whichresults in the excitation of outer electrons to higher energy level. For example, F2, has yellow,Cl2 , greenish yellow, Br 2, red and I2, violet colour

5.The enthalpy of dissociation ofF2 is less compared to that of Cl2


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A reason for this anomaly is therelatively large electron-electron repulsion among the lone pairsin F2 molecule due to smaller size of F-atom where they are much closer to each other than incase of Cl2.

Cl Cl > Br Br > I I.

BDE decreases bcozatomic size and hence bond length increase.

Cl 2> Br 2>F 2>I 2

Question?

Although electron gain enthalpy of fluorine is less negative as compared to chlorine, fluorine is astronger oxidising agent than chlorine. Why?

Ans:- It is due to

(i) low enthalpy of dissociation of F-F bond

(ii) high hydration enthalpy of F

CHEMICAL PROPERTIES:-

1.Fluorine shows only -1 state . due to its high electronegativity.

2. The fluorine atom has nod orbitals in its valence shell and therefore cannot expand its octet.

3. Others show -1 , +1, +3, +5 and +7.

4. The chemical reactivity decreases down the group, bcoz the electronegativity decreases.

5. The Oxidising tendency also decreases down the group whereas the reducing tendencyincreases.

There is a regular decrease in the first ionization energy as we go down this column. As aresult, there is a regular decrease in the oxidizing strength of the halogens from fluorine toiodine.

F2 > Cl2 > Br 2 > I2

oxidizing strength

This trend is mirrored by an increase in the reducing strength of the corresponding halides.


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I- > Br - > Cl- > F-

reducing strength

6. A halide can oxidize any other halide having a higher atomic no.

F2+ 2X- 2F- + X2 ( X = Cl/Br/I)

Cl2 + 2X- 2Cl- + X2 ( X = Br/I)

2 I-(aq ) + Br 2(aq ) I2(aq ) + 2 Br -(aq )

2F2 + 2H2O 4HF + O2

X2 + H2O HX + HOX (X= Cl /Br)4I - + 4H+ + O2 2I2 + 2H2O

Anomalous proerties of Fluorine:-

1.It forms only one oxoacid while other halogens form a number of oxoacids (HOF).

2.Hydrogen fluoride is a liquid (b.p. 293 K) due to strong hydrogen bonding. Other hydrogenhalides are gases.

HYDRIDES:-

1.The order of boiling point is:-

HF > HI> HBr> HCl

HI has exceptionally higher bpt since it forms extensive H-bonding.

The remaining hydrides follow increase in bpt with increase in molar mass.

1. Acidic strength of these acids increases in the order: .

Reason:- BDE decreases.

HF > HCl > HBr > HI

2. The stability of these halides decreases down the group

HF > HCl > HBr > HI.


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Reason :- BDE decreases.

OXIDES:-

1. Fluorine forms two oxides OF2 and O2F2. However, only OF2 is thermally stable at 298 K.

These oxides are essentially oxygen fluorides because of the higher electronegativity of fluorinethan oxygen.

Uses:-

(i).Both OF2 and O2F2 are strong fluorinating agents.

(ii) O2F2 oxidises plutonium to PuF6 and the reaction is used in removing plutonium as PuF6 from spent nuclear fuel.

2.The thermal stability of oxides decreases in the order;

I > Cl > Br > F

Reason:-Metallic character decreases and hence ionic character decreases

3. ClO2 is used as a bleaching agent for paper pulp and textiles and in sewage-water treatment.

4.I2O5 is a very good oxidising agent and is used in the estimation of carbon monoxide.

5. The ionic character of the metal halides decreases in the order

MF >MCl > MBr > MI

Reason:- Electronegativity decreases.

If a metal exhibits more than one oxidation state, the halides in higher oxidation state will bemore covalent than the one in lower oxidation state.(Fajans rule)

For e.g., SnCl4, PbCl4, SbCl5 and UF6 are more covalent than SnCl2, PbCl2, SbCl3 and UF4 respectively.

QUESTION?:

Fluorine exhibits only 1 oxidation state whereas other halogens exhibit + 1, + 3, + 5 and + 7oxidation states also. Explain.

Ans:-Fluorine is the most electronegative element and cannot exhibit any positive oxidationstate. Other halogens haved orbitals and therefore, can expand their octets and show + 1, + 3, +5 and + 7 oxidation states also.


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CHLORINE:-

Preparation:-

It can be prepared by any one of the following methods:

(i) By heating manganese dioxide with concentrated hydrochloric acid.

MnO2 + 4HCl MnCl2 + Cl2 + 2H2O

However, a mixture of common salt and concentrated H2SO4 is used in place of HCl.

4NaCl + MnO2 + 4H2SO4 MnCl2 + 4NaHSO4 + 2H2O + Cl2

(ii) By the action of HCl on potassium permanganate.

2KMnO4 + 16HCl 2KCl + 2MnCl2 + 8H2O + 5Cl2

Manufacture of chlorine

(i) Deacons process : By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of CuCl2 (catalyst) at 723 K.

4HCl + O2 2Cl2 + 2H2O

CuCl2 (ii) Electrolytic process : Chlorine is obtained by the electrolysis of brine (concentrated NaClsolution). Chlorine is liberated at anode.

Properties

1. Reaction with meatls and non-meatlas:-

2Al + 3Cl2 2AlCl3;

2Na + Cl2 2NaCl;

2Fe + 3Cl2 2FeCl3 ;

P4 + 6Cl2 4PCl3

S8 + 4Cl2 4S2Cl2


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2. Reaction with hydrogen and compounds of hydrogen:-

It has great affinity for hydrogen. It reacts with compounds containing hydrogen to form HCl.

H2 + Cl2 2HCl

H2S + Cl2 2HCl + S

C10H16 + 8Cl2 16 HCl + 10C

3.With excess ammonia , chlorine gives nitrogen and ammonium chloride whereas with excesschlorine, nitrogen trichloride (explosive) is formed.

8NH3 + 3Cl2 6NH4Cl + N2;

(excess)

NH3 + 3Cl2 NCl3 + 3HCl(excess)

4..With cold and dilute alkalis chlorine produces a mixture of chloride and hypochlorite butwith hot and concentrated alkalis it gives chloride and chlorate.

2NaOH + Cl2 NaCl + NaOCl + H2O

(cold and dilute)

6 NaOH + 3Cl2 5NaCl + NaClO3 + 3H2O

(hot and conc.)

5.With dry slaked lime it gives bleaching powder.

2Ca(OH)2 + 2Cl2 Ca(OCl)2 + CaCl2 + 2H2O

The composition of bleaching powder is Ca(OCl) 2.CaCl 2.Ca(OH) 2.2H 2O.

6.Chlorine water on standing loses its yellow colour due to the formation of HCl and HOCl.Hypochlorous acid (HOCl) so formed, gives nascent oxygen which is responsible for oxidising

and bleaching properties of chlorine.(i) It oxidises ferrous to ferric, sulphite to sulphate, sulphur dioxide to sulphuric acid and iodineto iodic acid.

2FeSO4 + H2SO4 + Cl2 Fe2(SO4)3 + 2HCl

Na2SO3 + Cl2 + H2O Na2SO4 + 2HCl


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SO2 + 2H2O + Cl2 H2SO4 + 2HCl

I2 + 6H2O + 5Cl2 2HIO3 + 10HCl

(ii) It is a powerful bleaching agent; bleaching action is due to oxidation and therefore it is

permanent. Cl2 + H2O 2HCl + [O]

Coloured substance + [O] Colourless substance

It bleaches vegetable or organic matter in the presence of moisture.

Bleaching effect of chlorine is permanent .

Uses of Chlorine : It is used (i) for bleaching woodpulp (required for the manufacture of paperand rayon), bleaching cotton and textiles, (ii) in the extraction of gold and platinum (iii) in themanufacture of dyes, drugs and organic compounds such as CCl4, CHCl3, DDT, refrigerants, etc.(iv) in sterilising drinking water and (v) preparation of poisonous gases such as phosgene(COCl2), tear gas (CCl3 NO2), mustard gas (ClCH2CH2SCH2CH2Cl).

QUESTION:-

Write the balanced chemical equation for the reaction of Cl2 with hot and concentrated NaOH. Isthis reaction a disproportionation reaction? Justify.

Ans:- 3Cl2 + 6NaOH 5NaCl + NaClO3 + 3H2O

Yes, chlorine from zero oxidation state is changed to 1 and +5 oxidation states.Hydrogen Chloride

Preparation

In laboratory, it is prepared by heating sodium chloride with concentrated sulphuric acid.

NaCl + H2SO4 NaHSO4 + HCl

420K

NaHSO4 + NaCl Na2SO4 + HCl

823K

HCl gas can be dried by passing through concentrated sulphuric acid.

Properties


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1.It reacts with NH3 and gives white fumes of NH4Cl.

NH3 + HCl NH4Cl

2.When three parts of concentrated HCl and one part of concentrated HNO3 are mixed, aquaregia is formed which is used for dissolving noble metals, e.g., gold, platinum.

Au + 4H+ + NO3- + 4Cl- AuCl4- + NO + 2H2O

3Pt + 16H+ + 4NO3- +18Cl- PtCl62- + 4NO + 8H2O

3.Hydrochloric acid decomposes salts of weaker acids, e.g., carbonates, hydrogen carbonates,sulphites, etc

Na2CO3 + 2HCl 2NaCl + H2O + CO2

NaHCO3 + HCl NaCl + H2O + CO2

Na2SO3 + 2HCl 2NaCl + H2O + SO2

Uses of HCl:- It is used (i) in the manufacture of chlorine, NH4Cl and glucose (from cornstarch), (ii) for extracting glue from bones and purifying bone black, (iii)in medicine and as alaboratory reagent.

QUESTION:-

When HCl reacts with finely powdered iron, it forms ferrous chloride and not ferric chloride.Why?

Ans:-Its reaction with iron produces H2.

Fe + 2HCl FeCl2 + H2

Liberation of hydrogen prevents the formation of ferric chloride.

Oxoacids of Halogens


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INTERHALOGEN COMPOUNDS

The compounds of halogens formed amongst themselves are called interhalogen compounds.

1. The interhalogen compounds can be prepared by the direct combination or by the action ofhalogen on lower interhalogen compounds

Cl2 + 3F2 2ClF3

(Excess)

I2 + 3Cl2 2ICl3

(Excess)

Br 2 + 5F2 2BrF5

(Excess)

2. They are all covalent in nature.

3. More reactive than halogens (except Fluorine).

This is because XX`bond in interhalogens is weaker than XX bond in halogens except FF bond.

3. They are diamagnetic as they do not contain any unpaired electron.


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4. XX + H2O HX + HOX. (X= smaller halogen)

5.Shapes:-

XX3 -------------- Bent T- shaped

XX5 --------------- Square pyramidal

XX7 (IF7) ------- Pentagonal bipyramidal.

Shape of BrF3:- Bent T shaped.

Uses :

1. These compounds can be used as non aqueous solvents.2. Interhalogen compounds are very useful fluorinating agents.3. ClF3 and BrF3 are used for the production of UF6 in theenrichment of U-235.

U(s) + 3ClF3(l) UF6(g) + 3ClF(g)

GROUP 18 ELEMENTS.

1.Group 18 consists of six elements: helium, neon, argon, krypton, xenon and radon.

2.Electronic configuration isns2np6

3.They have very high ionization enthalpy due to stable configuration.

4..All these are gases and chemically unreactive. They form very few compounds. Because ofthis they are termed noble gases.

5.All the noble gases except radon occur in the atmosphere. Their atmospheric abundance in dryair is ~ 1% by volume of which argon is the major constituent.


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Helium and sometimes neon are found in minerals of radioactive origin e.g., pitchblende,monazite, cleveite. The main commercial source of helium is natural gas.

Xenon and radon are the rarest elements of the group.

Radon is obtained as a decay product of Radium-226.

226 222 4

Ra Rn + He

88 86 2

Because radon is highly radioactive, it is difficult to study the chemistry of radon.

6.They have very low melting and boiling points because the interatomic interaction in theseelements isweak dispersion forces. Helium has the lowest boiling point (4.2 K) of any knownsubstance. It has an unusual property of diffusing through most commonly used laboratorymaterials such as rubber, glass or plastics.

7.In general, noble gases are least reactive. Their inertness to chemical reactivity is attributed tothe following reasons:

(i) The noble gases except helium (1s2) have completely filledns2np 6 electronic configuration intheir valence shell.

(ii) They have high ionisation enthalpy and more positive electron gain enthalpy.(since they donot have any tendency to accept an additional electron as their outermost orbits are completelyfilled)

8.Xenon has lower ionisation enthalpy, because of large size of xenon.

9. Xenon reacts with only oxygen and fluorine atoms because these two elements are of veryhigh polarizing capacity.

10.The fact that the first IE of xenon is comparable with that of molecular oxygen prompted NeilBartlett to study the chemistry of xenon compounds.(he understood this from the compoundO2PtF6, which he prepared )

The first compound of xenon prepared was XePtF6

Question?

Why are the elements of Group 18 known as noble gases ?


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The elements present in Group 18 have their valence shell orbitals completely filled and,therefore, react with a few elements only under certain conditions. Therefore, they are known asnoble gases.

(a) Xenon-fluorine compounds

Xenon forms three binary fluorides, XeF2, XeF4 and XeF6 by the direct reaction of elementsunder appropriate experimental conditions.

XeF6 can also be prepared by the interaction of XeF4 and O2F2 at 143K.

XeF4 + O2 F2 XeF6 + O2

Properties:-

1.XeF2 is hydrolysed to give Xe, HF and O2.

2XeF2 (s) + 2H2O(l) 2Xe (g) + 4 HF(aq) + O2(g)

2.Xenon fluorides react with fluoride ion acceptors to form cationic species and fluoride iondonors to form fluoroanions.

XeF2 + PF5 [XeF]+ [PF6] ;

XeF4 + SbF5 [XeF3]+ [SbF6]

XeF6 + MF M+

[XeF7]

(M = Na, K, Rb or Cs)

(b) Xenon-oxygen compounds

Hydrolysis of XeF4 and XeF6 with water gives Xe03.

6XeF4 + 12 H2O 4Xe + 2Xe03 + 24 HF + 3 O2

XeF6 + 3 H2O XeO3 + 6 HFStructures of xenon compounds:-


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XeF 4

F

F F

F

Xe

..

..

Uses:-

1.Helium is a non-inflammable and light gas. Hence, it is used infilling balloons formeteorological observations. It is also used ingas-cooled nuclear reactors. Liquid helium (b.p.4.2 K) finds use as cryogenic agent for carrying out various experiments at low temperatures. Itis used to produce and sustain powerful superconducting magnets which form an essential part ofmodern NMR spectrometers and Magnetic Resonance Imaging(MRI) systems for clinicaldiagnosis.It is used as a diluent for oxygen in modern diving apparatus because of its very lowsolubility in blood.

2. Neon is used in discharge tubes and fluorescent bulbs for advertisement display purposes.

3.Argon is used mainly to providean inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) andfor filling electric bulbs.

It is also used in the laboratory for handling substances that are air-sensitive.

4.Xenon and Krypton are used in light bulbs designed for special purposes.


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Important chemical equations

1. NH4CI +NaNO2 N2+2H2O+NaCl

2 (NH4)2Cr 2O7 N2+4H2O+Cr 2O3

3. 2NH4Cl+Ca(OH)2 2NH3+ H2O +CaCl2

4. 2FeCl3+3NH4OH Fe(OH)3+2NH4Cl

5. Cu2++4NH3 [Cu(NH3)4]2+

6. 4NH3+5O2 Pt 4NO+6H2O

500K ; 9 bar


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7. 2NO+O2 2NO2

8. 3NO2+H2O 2HNO3+NO

9. 3Cu+8HNO3 3Cu(NO3)2+2NO+H2O

10. Cu+4HNO3 Cu(NO3)2+2NO2+4H2O

11. I2+10 HNO3 2HIO3+10 NO2+4H2O

12. P4+20 HNO3 4H3PO4+20 NO2+4H2O

13. NO3- +3Fe3++4H+ NO+ 3Fe2++2H2O

14. [Fe(H2O)6]2++NO [Fe(H2O)5 NO]2++H2O

15. P4+3NaOH+3H2O PH3+3NaH2PO2

16. PCl3+3H2O H3PO3+3HCl

17. PCl5+H2O POCl3+2 HCl

18. POCl3+3H2O H3PO4+3HCl

19. Al2O3+6HCl+9H2O 2[Al(H2O)6]3++6Cl-

20 Al2O3. +6NaOH+3H2O .2Na3[Al(OH)6]

21. PbS+4O3 PbSO4+4O2

22. 2I- +H2O+O3 2OH-+I2+ O2

23. 2Fe3+ + SO2 + 2H2O 2Fe2++ SO42- +4H+

24. 2MCl+H2SO4 HCl+M2SO4 (M= any alkali or alkaline earth metal)

Conc.H2SO4

25. C12H22O11 12C+11H20

26. C+Conc.H2SO4 CO2+2SO2+2H2O

27. MnO2+4HCl MnCl2+Cl2+2H2O

28. 2KMnO4+16HCl 2KCl+2MnCl2+8H2O+5Cl2

29. 2NaOH+Cl2 NaCl+NaOCl+ H2O

30. 6NaOH+3Cl2 5NaCl+NaClO3+3 H2O


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31. 2Ca(OH)2+2Cl2 Ca(OCl)2+CaCl2+2H2O

32. Na2SO3+Cl2+H2O Na2SO4+2HCl

33. I2+ 6H2O +5Cl2 2HIO3+10 HCl

34. Cl2+3F2 2ClF3

35. I2+3Cl2 2ICl3

36. Br 2+3F2 2BrF3

37. Xe +F2 673k ; 1bar Xe F2

38. Xe+ 2F2 873k,7bar Xe F4

39. Xe+3F2 573k,60-70bar Xe F6

40. XeF2+PF5 [XeF]+[PF6]-

41. XeF6+NaF Na+[XeF7]-

42. XeF6+3H2O XeO3+6HF

HOTS

1. What is called inert pair effect?2. As we go down a group in the p-block the stable oxidation state decreases by 2 units. Explain.3. Why do the group 15 elements have very high I.E?

4. There is only very small increase in size from As Bi. Why?5. Molecular nitrogen exist as a gas whereas phosphorus is solid at room temperature. Why?6. PCl5 exists whereas NCl 5 does not why?7. N does not show allotropy. Why?8. N does not catenate. Why?9. Bi shows +3 states. Why10. Why is NF 3 stable whereas NCl 3 is not?11. Why is BiF3 highly ionic?12. Which is more covalent BiF 5 or Bif 3?13. NH3 is a Lewis base. Explain.14. Why is NH 3 a stronger base than BH 3.15. Arrange the hydrides of group 15 elements in the

(a) increasing order of basicity(b) increasing order of stability (c) Increasing order of reducing nature

16. Complete (NH 4)2 Cr2O7 ?

17. Molecular Nitrogen is highly unreactive. Why?18. Explain Habers process. (optimum conditions and catalyst)19. Silver chloride dissolves in aqueous ammonias. Explain.20. Complete Cu 2+(aq) + NH3(aq) ? 21. Shapes of oxides of nitrogen.


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22. Why do NO 2 and NO dimerise?23. What is the covalence of N in (a) N 2O5 (b) N 2O4 ?24. Explain Ostwald process of manufacturing HNO 3.25. Draw the shape of HNO 3. Why is it monobasic?26. Explain the chemistry of the Brown ring test.27. Complete and balance P 4 + NaOH + H2O ? 28. Why is white phosphorus less stable and more reactive?29. Write any two differences between white and red phosphorus.30. Mention any two uses of phosphine.31. Bond angle in PH 4+ is higher than that in PH 3. Why?32. Why does PCl 3 fumes in moist air?33. Complete and balance (a) P 4 + SOCl2 ? (b) P 4 + SO2Cl2 ? (c) HgCl 2 + PH3?

(d) CuSO4 + PH3? 34. Why does PCl 5 fumes in moist air?35. Draw the shape of (a) PH 3 (b) PCl3 (c) PCl5 36. Complete and balance (a) Ag + PCl 5? (b) Sn + PCl 5? 37. PCl5 in solid state exists as an ionic solid. Explain.

38. All the five bonds in PCl 5 are not equivalent. Explain.39. Draw the structure of (a) Phosphoric Acid (b) phosphorus Acid (c) Hypo phosphorus acid

Discuss the basicity of each of them.40. Phosphorus acid disproportionates. Write the equation41. Hypo Phosphorus acid is a better reducing agent than phosphorus acid.Explain.42. How is N 2 prepared in lab? (ans: NH 4Cl + NaNO2

N2 + 2H20 + NaCl)43. NH3 is a stronger base than BiF 3. Why?44. NH3 form intermolecular H-bond whereas PH 3 does not. Why?45. Write the equation for the reaction of PCl5 with heavy water. (ans: PCl 5 + 4D2OD3PO4 +5DCl)46. Hypo phosphorus acid is a reducing agent. Explain.47. Group 16 elements have lower I.E than group 15 elements. Why?

48. Oxygen has less negative electron gain enthalpy than S. Why?49. Oxygen is a gas at room temperature whereas Sulphur is a sold. Why?50. Oxygen has lower melting point and boiling point than Sulphur. Why?51. Oxygen shows -2 oxidation state preferably. Why?52. OF2 exists whereas OCl 2 does not. Why?53. Oxygen does not show covalency beyond 4. Why?

ORSF6 exists where as OF6 does not. Why?

54. OF2 is known as Oxyfluoride but not flourooxide. Why?


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QUESTIONS WITH ANSWERS15 th GROUP

1. The Bi (V) compounds are unknown except BiF5 .Why?Due to inert pair effect, +5 oxidation state of Bi is unstable

2. Nitrogen exists as a gas in elemental state , whereas other elements of the group existassolid .Why?Due to ability of nitrogen to form p - p multiple bond , it exists as discrete molecules

Of N2 .3. The tendency of catenation for Nitrogen is less than Phosphorous . Why?

N-N bond is weaker than P-P bond due to inter electronic repulsion between nonbonding pair of electrons in Nitrogen owing to its small size .4. Arrange the hydrides of 15 th group elements in the decreasing order of the propertymentioned

a. Thermal stability : NH 3 > PH3>AsH3>SbH3>BiH3b. Basic strength : NH 3 > PH3>AsH3>SbH3>BiH3 c. Reducing character : BiH 3 > SbH3 >AsH3>PH3> NH3

5. Arrange the oxide E 2O3 of 15 th group element in the decreasing order of acid strengthN2O3> P2O3>As2O3>Sb2O3>Bi2O3

6. Nitrogen doesnt form pentahalides . Why?Due to non availability of d orbitals in Nitrogen to expand its covalency beyond 4.

7. NH3 has exceptionally higher boiling point compared to the other hydrides of 15 th group.Why?Due to strong inter molecular association in NH 3 through H- bonding

8. NH3 is most basic among the hydrides of 15 th group elements . Why?

Due to small size of Nitrogen the availability of lone pair electron in NH3 is more.9. BiH3 is the strongest reducing agent among the hydrides of 15 th group elements .Why?

Bcause Bi-H bond is the weakest10. The pentahalides of 15 th group elements are more covalent than their trihalides .Why?

The +5 oxidation state of the element in their penta halides is more polarizing than the+3 state of elements in their trihalides .

11. The thermal stability of BiH3 is the lowest among the hydrides of 15 th group elementsWhy?Bi-H bond is the weakest bond due to its small bond dissociation enthalpy .

12 Dinitrogen ( N 2) is inert at room temperature .Why?Due to very high bond enthalpy of N= N

13. How is Nitrogen prepared in pure form ?By thermal decomposition of Sodium/Barium azideBa(N3)2 Ba + 3N2 2NaN 3 2Na + 3N 2

14. How is NH 3 manufactured by Haber processN2 (g) + 3H2(g) 2NH3(g) Temperature : 700K Pressure : 200At.Catalyst : Iron oxide Promoters : K 2O and Al 2O3


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15. AgCl is soluble in NH 3 . Why ?Due to formation of a soluble complex with NH 3. AgCl (s) + NH3(aq) [Cu(NH 3)4]

2+ 16. How does NH 3 react with Cu 2+ (aq) ?

Cu2+ + 4NH3 [Cu(NH3)4]2+ 17. NO 2 undergoes dimerisation .Why?

NO2 is an odd electron molecule . So on dimerisation it is converted to N 2O4 whichcontains even no .of electrons . (Diagram)

18. NO being an odd electron molecule , doesnt undergo dimerisation . Why?The unpaired electron in NO is delocalized and gets stabilized .(Diagram)

19. How is HNO 3 manufactured by Ostwalds process .Pt/Rh/ 500K ,9bar

4NH3(g) + 5O2 (g) 4NO(g)2NO(g) + O 2(g) 2NO 2(g)3NO2(g) + H2O (l) 2HNO3 (aq) + NO (g)

20. What is the Chemistry of Brown ring test ?NO3

- + 3Fe 2+ + 4H+ NO + 3Fe 3+ + 2H2O[Fe(H2O)6]2+ + NO [Fe(H2O)5(NO)]2+ + H2O

21. Methods of preparation of oxides of Nitrogen .(Table 7.3)22. Reactions of con.HNO 3 with Zn, Cu, I2, C, S 8, P4 23. How does white P 4 react with boiling NaOH ?

P4 + 3NaOH + 3H 2O PH3 + 3NaH 2PO2 24. White Phosphorous is more reactive than red phosphorous .Why?

In white phosphorous there is angular strain in P4 molecule .so it is less stable and morereactive compared to red phosphorous.

25. What are the differences between white phosphorous and red phosphorous?a. White P consists of discrete tetrahedral P4 molecules whereas red p consists of chain

of P 4 tetrahedra.b. White P is soluble in CS 2 while red P is insoluble in CS 2 .c. White P glows in darkness whereas red P doesnt glow .d. white P is more reactive than red P

26. White P glows in darkness .Why?Due to chemiluminescence .

27. White P catches fire spontaneously .Why?Because its ignition temperature is lower than atmospheric temperature.

28. How are and Black Phosphorous prepared ? Black P is prepared by heating red P in a sealed tube at 803k . black P is prepared by heating white P under high pressure.

29. Impure PH 3 is inflammable. Why?Due to the presence of impurities like PH 3 or P 4 vapours which are inflammable .

30. How is PH 3 purified ?Impure PH 3 is absorbed in HI to form PH 4I which on treating with KOH gives off PH 3.

31. How does Ca 3P2 react with HCl?Ca3P2 + 6HCl 3CaCl2 + 2PH3

32. How does PH 3 react with a. CuSO 4 b. HgCl2


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3CuSO4 + 2PH3 Cu3P2 + 3H2SO43HgCl2 + 2PH3 Hg3P2 + 6HCl

33. Show that PH 3 is Basic .PH3 is a Lewis acid due to the presence of a lone pair electron on P atom .It reacts withacids like HI and gives salt .

PH3 + HI PH4I34. Bond angle in PH 4+ is higher than that in PH 3 . Why?

In PH3 there are 3 bond pairs and 1 lone pair of electrons , whereas in PH 4+ there areonly 4 bond pairs of electrons . Due to greater repulsion between lone pair and bond

pair in PH 3 as compared to bond pair bond pair repulsion in PH 4+ , the bond angle in PH 3

is less than that in PH 4+.

35. PCl3 fumes in moist air .Why?Due to formation of HCl gas with water.PCl3 + 3H2O H3PO3 + 3HCl

36. What happens when PCl 5 is heated ?It decomposes to give PCl

3 and Cl

2 .

37. Why does PCl 5 fumes in moist airDue to formation of HCl gas with water.PCl5 + 4H2O H3PO4 + 5HCl

38. All the five P-Cl bonds in PCl 5 are not equivalent . Why?PCl5 has a triagonal bipyramidal structure with 3 P-Cl bonds in equatorial position and 2

P-Cl bonds in axial positions . Since axial bonds experience more repulsion from equatorialbonds ,they are slightly longer than equatorial bonds .39. H 3PO3 undergoes disproportionation .Why?

Due to less stability of +3 oxidation state of P compared to its +5 and -3 oxidation state .4H3PO3 3H3PO4 + PH3

40. H 3PO2 is a reducing agent .Why?Due to the presence of 2 P-H bonds.Eg. 4AgNO3 + 2H2O + H3PO2 4Ag + 4HNO3 + H3PO4

41. H 3PO3 is a dibasic acid though there are 3 hydrogen atoms.Why?In H3PO3 there are only 2 H atoms which are ionisable ( due to 2 P-OH bonds ).The third

H atom is bonded to P , so not ionisable .42. How Many types of salts are formed by the following acids?

a) H3PO3 - 2 types (basicity is 2)b) H3PO4 -- 3 types (basicity is 3)c) H3PO2 -- 1 type (basicity is 1)

43. Solid form of PCl 5 is conducting. Why?In solid form PCl 5 exists as an ionic compound [PCl 4]+ [PCl6]- 44. CN- is a known compound whereas CP- is not known.Why?

Nitrog en can form p - p bond with carbon .whereas Phosphorous cant form p - pwith carbon.

GROUP-16TH 1. There is a large difference in melting and boiling points of oxygen and sulphur.Why?


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Oxygen exists as a diatomic molecule O 2 whereas Sulphur exists in a puckeredarrangement of S 8 molecules . Therefore there is strong intermolecular force in sulphur .2. Name two compounds in which Oxygen shows positive oxidation state .

OF2(-2) and O 2F2 (-1)3. In the elemental form O 2 is a gas whereas other elements of the group are solids .Why?

Oxygen can form p - p multiple bond with itself and form O 2 molecules . But othermembers of the group cant form p - p multiple bonds with their atoms and so they formpuckered arrangement of their polyatomic molecules .4. Oxygen shows positive oxidation state in compounds with Fluorine. Why?

Oxygen is less electronegative than Fluorine .5. First ionization enthalpy of 16 th group elements is less than that of 15 th group elements.Why?

15 th group elements have extra stable half filled P orbitals as their valence orbital, so alarge amount of energy is required to remove one valence electron .6. H2O is a liquid whereas all the other hydrides of 16 th group are gases. Why?

Due to strong intermolecular H-bonding in H2O

7. Arrange the Hydrides of 16 th group elements in increasing order of the propertymentioned below

a) Thermal stability : H 2Po


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PbS (s) + 4O 3(g) PbSO 4(s) + 4O 2 (g)2I-(aq) + O 3(g) + H2O (l) 2OH-(aq) + I2 (s) + O 2(g)

16. How is O 3 estimated quantitatively ?O3 is treated with an excess of KI solution buffered with a borate buffer , the iodine so

liberated is estimated by titrating with a saturated solution of Sodium thiosulphate solution .

From the amount of iodine liberated the amount of O3 can be estimated .2I-(aq) + O 3(g) + H2O (l) 2OH-(aq) + I2 (s) + O 2(g)

17. How does the depletion of O 3 take place in the upper atmosphere ?The Nitrogen oxides emitted by supersonic jet aeroplanes depletes the O 3 layerNO (g) + O3 (g) NO2(g) + O2(g)

18. The O-O bonds in O3 are identical .Why?Due to resonance both O-O bonds get partial double bond character and are identical.

19. Sulphur in the vapour phase shows paramagnetism .Why?In the vapour form sulphur exists as a diatomic molecule which contains two unpaired

electrons in the antibonding pi molecular orbital like O2 .20. The behavior of SO 2 is like CO2 .Explain .

SO2 reacts with alkali solution in the similar way that CO2 reacts.2NaOH + SO 2 Na2SO3 + H2ONa2SO3 + H2O + SO2 2NaHSO 3

21. How is SO 2 gas detected ?So2 gas on passing through acidified KMO4 solution , the purple colour of KMnO4 is

discharged .

5SO2(g0 + 2MnO 4-(aq) + 2H 2O 5SO42- (aq) + 2Mn 2+ + 4H+

22. Both S-O bonds in SO 2 are identical. Why?Due to resonance both S-O bonds are getting partial double bond character and are

identical. (Diagram)23. Structure of oxoacids of Sulphur (From Text Book )24. How is H 2SO4 manufactured by Contact Process ?

S (s) + O2(g) SO2(g)

V2O5 / 720K , 2 bar

2SO2(g) + O2 (g) 2SO3 (g)

SO3(g) + H2SO4 H2S2O7 H2S2O7 + H2O 2H2SO4

Reactions of Con H 2SO4 refer text book

GROUP 17TH 1. Mention one source each for F, Br& I

F- Fluorspar (CaF 2) BrSea water I- Chile saltpeter.2. Halogens have very little tendency to lose electrons .Why?

Due to their high ionization enthalpy.3. Halogens have max. negative electron gain enthalpy. Why?


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Due to a) Small size b) high effective nuclear charge c) they need one electron toattain stable noble gas configuration .4. The electron gain enthalpy of Fluorine is less negative than Chlorine .Why?

Due to small size of Fluorine , there is strong inter electronic repulsion in the small 2porbital is high.

5. All halogens are coloured .Why?Due to absorption of radiation in the visible region which results in the excitation of

outer electrons to higher energy levels .6. The bond dissociation enthalpy of F 2 is smaller than that of Chlorine .Why?

Due to large electron electron repulsion among the lone pairs of electrons in Fluorine7. Fluorine is a strong oxidizing agent than Chlorine .Why?

This is due to a). Low bond enthalpy of F 2. b). high hydration enthalpy of F - 8. Fluorine doesnt show positive oxidation state.Why?

Due to its highest electronegativity .9. Fluorine cant expand its covalency beyond one .Why?

Due to absence of vacant d orbital.10. The oxidizing tendency of halogens decreases down the group. Why?

Due to a) decreasing electron gain enthalpy b) decreasing hydration enthalpy of X - 11. What happens when F 2 gas is passed through solutions of a) KCl b)KBr c) KI

Fluorine being more reactive oxidizes the halides to the respective halogens .KCl (aq) + F2 (g) 2KF (aq) + Cl2(g)KBr (aq) + F2(g) 2KF(aq) + Br2(l)KI(aq) + F2 (g) 2Kf(aq) + I2(g)

12. How does F 2 gas react with water ?F2 oxidises water to oxygen gas; F 2(g) + 2H2O (l) 4HF(aq) + O 2(g)

Bcoz, F is more electroneg than O13. How do Chlorine and Bromine react with water ?

Cl2(g) + H2O(l) HCl (aq) + HOCl (aq)Br2(l) + H2O(l) HBr(aq) + HOBr(aq)

14. What are the reasons for the anomalous behavior of Fluorine ?a) small size b) highest electronegativity c) low F-F bond dissociation enthalpyd) non availability of vacant d orbitals in the valence shell.

15. Most of the compounds of Fluorine are exothermic. Why?Due to small size and strong bond formed by Fluorine with atoms of other elements .

16. Fluorine forms only one oxoacid HOF . Why?Due to absence of vacant d - orbitals in its valence shell.

17. HF is a liquid . Why?Due to strong intermolecular H-bonding18. Arrange the hydrides of 17 th group elements in the increasing order of the propertymentioned .

Acid strength : HF


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20. What is the use of O 2F2 ?Used for the removal of Pu from the spent nuclear of nuclear power plant .

21. What is the use of ClO 2 ?Used in the bleaching of paper pulp and textiles and in water treatment .

22. Name the oxide of halogens used in the estimation of CO.I2O5

23. Which is more covalent SnCl 4 or SnCl2 and why?SnCl4 , because the higher oxidation state of the metal is more polarizing than its lower

oxidation state .24. How does Cl 2 reacts with a) cold dilute NaOH b) hot concentrated NaOH

Cold and dilute NaOH2NaOH + Cl2 NaCl + NaOCl + H2OHot and concentrated NaOH6NaOH + 3Cl 2 5NaCl + NaClO3 + 3H2O

25. How is Bleaching powder manufactured ? What is its composition ?By passing Cl 2 gas through dry slaked lime .2Ca(OH) 2 +2Cl2 Ca(OCl)2 + CaCl2 + 2H2OComposition is Ca(OCl) 2.CaCl2.Ca(OH)2.2H2O

26. Chlorine water loses its yellow colour on standing .Why?Due to the formation of HCl and HOCl . Cl 2 + H2O HCl +HOCl

26. Give the reason for the bleaching and oxidizing properties of Chlorine .Moist Chlorine gives HCl and HOCl . HOCl decomposes to give HCl and nascent oxygen

which is responsible for oxidizing and bleaching properties . Bleaching action is due to oxidationCl2 + H2O 2HCl + (O)Coloured substance + (O) colourless substance .

27. Name two poisonous gases that can be prepared from Chlorine .a) Phosgene (COCl 2) b) Tear gas (CCl 3NO2)

28. How does moist Chlorine react with I 2 ?I2 + 6H2O + 5Cl2 2HIO3 + 10HCl

29. What is aquaregia ? What is its use ?Aquqregia is a mixture of Con.HCl and Con.HNO 3 in the ratio 3:1. It is used for dissolving

noble metals like Gold and platinum.Au + 4H+ + NO3

- + 4Cl- AuCl4- + NO + 2H2O

30. When HCl reacts with finely powdered Iron , it forms ferrous chloride and not ferricchloride .Why?

HCl reacts with Iron and producesH

2 .Fe + 2HCl FeCl2 + H2

Liberation of hydrogen prevents the formation of ferric chloride.31. Write the geometry of the following interhalogen compounds .

a) ClF (XX1) : Linear.b) ClF3 (XX3) : Bent T shape.c) BrF5 (XX5) : Square pyramidald) IF5 : Pentagonal bipyramidal .


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32. Interhalogen compounds are more reactive than halogens except F 2 .Why?X-X bond in interhalogens is weaker than X-X bond in halogens except F-F bond .

33. Name the interhalogen which is used in the enrichment of Uranium?ClF3.

34. Write the produt of Hydrolysis of the following interhalgens .

a) XX : XX + H2O HX + HOXb) XX3 : XX3 + 2H2O 3HX + HOXOc) XX5 : XX5 + 3H2O 5HX + HOXO2 d) XX7 : XX7 + 4H2O 7HX + HOXO3

GROUP 18TH 1. The elements of group18 are known as noble gases . Why?

They have completely filled valence shell . So they react with a few elements only undercertain conditions .2. 18 th group elements have large positive values of electron gain enthalpy .Why?

Due to their stable electronic configuration they have no tendency to accept theelectron .3. 18 th group elements have very low melting and boiling points . why?

Due to very weak intermolecular interaction, i.e.,weak dispersion forces .4. Noble gases are liquefied at very low temperatures .Why?

Due to weak intermolecular forces .5. Noble gases are chemically inert .Why?

Due to a) completely filled valence shell. b) High ionization enthalpy c) positiveelectron gain enthalpy .6. What inspired N. Bartlett for carrying out reaction between Xe and PtF 6 ?

The first ionization enthalpy of molecular oxygen was almost identical with that of Xe .7. What was the compound prepared by N. Bartlett that led to the discovery of first noblegas compound ?

O2+PtF6-

8. What was the first noble gas compound prepared ?Xe+PtF6-

9. XeF2 is a linear molecule without bend .Why?XeF2 has 3 lone pair and 2 bond pair electrons .The 2 bond pairs are occupying the axial

positions and 3 lone pairs are occupying the equatorial positions making 120 0 with each otherand 90 0 with the bond pairs . Since the bond pairs are experiencing same amount of repulsionfrom the lone pairs the molecule is linear without bend.

10. Give reactions to show that Xe fluorides act as both Lewis Acid and Lewis BaseLewis Acid : XeF6 + NaF M+ [XeF7]- Lewis Base : XeF 2 + PF5 [XeF]+[PF6]-

11. write a balanced reaction between water and a) XeF4 b) XeF66XeF4 + 12H2O 4Xe + 2XeO3 + 24HF + 3O2 XeF6 + 3H2O XeO3 + 6HF

12. Why is He used in diving apparatus ?Because He gas is very light and its solubility in water is very less.


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13. Why is it difficult to study the chemistry of Radon ?Because it is radioactive .

14. Give the formula and describe the structure of a noble gas species which is isostructural

with a) ICl 4-

b) IBr2-

c) BrO3-

a) XeF4 : Square pyramidal with 2 lone pairs above and below the plane .b) XeF2 : Linear with 3 lone pairs occupying the equatorial position .c) XeO3 : Pyramidal with a lone pair electron at the apex.

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The P-block Elements(Summary)

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