1. Basic Concepts P-block Class 12

8/10/2019 1. Basic Concepts P-block Class 12

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CLASS XII p-BLOCK ELEMENTSBASIC CONCEPTS/IMPORTANT FORMULA/EQUATIONS

Group 15 Eleme!-I!ro"u#!$o

Group 15 of the long form periodic table consists of five elements: Nitrogen (N), Phosphorus (P),

Arsenic (As), Antimony (b) and !ismuth (!i)" #hese elements are collectively called the elements ofnitrogen family% &N$#o'e ()m$l*+

Nitrogen and phosphorus are non-metals$ arsenic and antimony are semi-metals or metalloids,

%hereas bismuth is metallicalthough not so strongly"

Proper!$e, o( Group 15 Eleme!,

Ele#!ro$# Co($'ur)!$o

#he elements of Group 15 have five electrons in their outermost shell" #herefore, the outer electronic

configuration of nitrogen family elements can be %ritten as ns2 np3.

(i) A!om$# r)"$$Atomic radii of Group 15 elements are smaller than those of Group 1& elements" #his is due to the

increased effective nuclear charge (Zeff)for Group 15 elements" #he atomic radius gradually increase as one

goes from N to !i" #his is due to the addition of ne% electronic shell at each element do%n the group"

(iii) Io$,)!$o eer'*

#he ionisation energies of Group 15 elements are much higher than the corresponding values of the

Group 1& elements"

'PANA#*+N: #hep orbitals in the valence shell of these elements are half-filled(ns2 np3)" #his

gives etra-stability to these electronic configurations" #his therefore, the ionisation energy of these

elements increases"

#he ionisation energy decreases in going from N to !i do%n the group"

'PANA#*+N: #he decrease in the ionisation energy do%n the group is due to an increase in theatomic si.e in going from N to !i"

(vi) Ele#!ro e')!$$!*

Group 15 elements are more electronegative than Group 1& elements" 'lectronegativity of this group

of elements sho%s a gradual decrease in going from N to !i (do%n the group)"

(v) O.$")!$o ,!)!e,

Group 15 elements have five electrons in their outermost shell, viz., ns/ np0" #hese elements can,

therefore, complete their outer shell in the follo%ing t%o %ays"

(a) !y electron transfer

(b) !y electron sharing

&A+ B* ele#!ro !r),(er%

#o complete their outer shell, these elements should either lose 5 valence electrons, or gain 0 more

electrons" ue to their smaller si.e and higher nuclear charge, nitrogen (N) and phosphorus (P) cannot lose

their five valence electrons" 2o%ever, these elements can accept three electrons to form nitride (N 03) and

phosphide (P03) anions" Nitrogen, because of its smaller si.e has higher tendency to form N 03 anion"

Phosphorus forms P03anions less readily"

Nitrogen and phosphorus form nitrides and phosphides respectively only %ith highly electropositive

elements, such as, %ith magnesium and calcium" +ther members of Group 15, i.e., As, b and !i do not

form 403type of anions because of their lo%er electronegativity" #he heavier elements of this group (b and

!i) tend to lose their electrons to form 40and 45cations" ince, the inert-pair effectbecomes more

prominent near at the bottom of the group hence Sb and Bi form only M3+cations, i.e., Sb3+and Bi3+" #he

45

ions do not eist, and the 5 oidation state is realised only through covalent bonding"Ques.-he + 3 state becomes more stable than + ! of Sb and Bi.

EXPLANATION: As %e go do%n the group, the tendency ofs-electrons in the valence shell to ta6e

part in chemical bonding decreases" he tendency of s-electrons to not participate in co"alent bond

formation is #no$n as the inert-pair effect.#he inert-pair effect becomes more operative to%ards the


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bottom of the group" #hus, for heavier elements of the group (e.g.,Sb and Bi.), the 0 state becomes more

stable than 5 state"

Nitrogen can form 1,/,0,& oidation states also %hen it reacts %ith oygen" Phosphorous sho%s

1,/,0,& oidation states in ooacids"

N0 N2 N NO NO NO0 NO NO5-0 - 3 41 4 40 42 45

&B+ B* ele#!ro ,)r$'%

'lements of Group 15 contain 5 valence electrons (ns/np0)" +ut of these five, three electrons are

unpaired electrons (px1,py1,pz1)" #hus, these elements can form three covalent bonds by mutual sharing" As

in the case of N20, P20, As20, b20and !i20: the t%os electrons remain on the atoms of these elements as

lone pair"

*f one of the t%os-electrons is promoted to a vacant d-orbital, then the total number of unpaired

electrons becomes 5" As a result, an atom of that element can ma6e five covalent bonds"

ince, all other elements (ecept N) have d-orbitals in their valence shell$ hence these elements can

form 5 covalent bonds" 7or eample, phosphorus forms P75, P8l5"

P*,$#)l Proper!$e, o( Group 15 Eleme!,(i) P*,$#)l ,!)!e )" o##urre#e

%itro&en is a &as, $hile rest of the four elements of this &roup are solids, under ordinaryconditions" Nitrogen forms about 9; by volume of the earth


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#he chemical behaviour of nitrogen differs considerably from that of the other elements of this

group" #his is due to the follo%ing reasons"

ue top*- p*overlap, N forms multiple bonds %ith itself as %ell as %ith carbon and oygen, e.g.,

#he tendency to form multiple bonds decreases as %e go do%n the group" *t is due to this reason that

elemental nitrogen eists as a diatomic (N/, N N) molecule" #he bond energy

of N N bond is very high (D&1 6? mol31)"

6ue !o er* $' 7o" eer'* o( N N 7o"8 $!ro'e $, )lmo,!

o-re)#!$e $ $!, eleme!)l (orm%

Phosphorus, arsenic, and antimony do not formp*- p*multiple bonds

hence these elements do not eist as diatomic molecules" #o satisfy their

valence shell these elements form tetratomic, tetrahedral molecules such as P&,

As&and b&" ince,P 9 P ,$'le 7o" $, mu# :e);er !) !r$ple N N 7o"8

e#e po,poru, $, more re)#!$e !) $!ro'e%

Eecently, a fe% compounds having P C 8, P 8, P C N, P C P and As C As groups %hich involve

p*- p*multiple bonding by phosphorus and arsenic have been synthesi.ed"

Phosphorus and the heavier members of the family do not readily form p*- p*multiple bonds

%hereas multiple bonding of the d*- p*type can occur readily for these elements"#he d*- p* bonding is particularly prominent for phosphorus as reflected in the formation of

compounds, such as, 3CP0and EN C P0" *n these compounds, thep-orbital of oygen or nitrogen atom

overlaps side%ays %ith the d-orbital of phosphorus atom to form d*- p*multiple bond"

Ques.(- %itro&en can not sho$ hi&her co"alency $hile other elements of ! th&roup can, $hy

'ns.(- As nitrogen has no d-orbitals in its valence-shell, therefore it can form at the maimum four covalent

bonds, e.g., in N2&, NE& etc" #he heavier members of the group can epand their valence shell and form

penta- and hea-coordinated derivatives such as P8l5, As75and P73" #he higher coordination numbers are

readily adopted %hen electronegative substituents are present" ince, N cannot epand its valence shell

beyond four hence it does not form pentavalent compounds such as N8l5, N75etc"

Ques.(- N$!ro'eis "ery less reacti"e then other elements of its &roup, $hy

he chemical beha"iour of these elements can be described by considerin& the formation of

"arious types of compounds as discussed belo$"

ydrides of /roup ! 0lements(-All Group 15 elements give hydrides of the types 42 0(%here 4 C N, P, As, b, !i), and 4 /2&

(%here 4 C N and P)"

Phosphine (P20) and hydrides of other heavier elements of this group are highly poisonous" ome general

characteristics of hydrides of Group 15 elements are given belo%"

1%Structure% All 420hydrides of Group 15 elements are covalent in nature" #he central atom (i.e.,

N, P, etc") aresp0hybridised" #hree hybrid orbitals form covalent bonds %ith 1s

orbitals of hydrogen atoms, %hile the fourth orbital is occupied by a lone-pair of

electrons" #his givespyramidal structureto these hydrides" Pyramidal structure

of ammonia (N20) molecule is sho%n in 7ig" "11"

+ther 420hydrides have similar structure" !ut, 242 bond angles are

different" 7or eample,

*"r$"e < N0 P0 A,0 S70 B$0

Bo" )'le < 13=> ?2> ?> ?1> ?3>Te 7o" )'le "e#re),e, ), !e ,$@e o( !e #e!r)l )!om $ *"r$"e, $#re),e,%


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01'%'45%: *n hydrides (420type), the central atom is surrounded by three bond pairs and

one lone pair of electrons" ue to the presence of lone pair of electrons on the central atom, the 242 angle

in 420hydrides are less than the tetrahedral angle of 1BDF /


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alides of /roup ! 0lements(-'lements of Group 15 form t%o types of halides, viz., trihalides :M13)andpentahalides :M1!).

All trihalides of N, P, As, b and !i ecept N* 0are 6no%n. %itro&en does not form pentahalides,

e.&., %9!, %;l!, %Br!and %4!due to the absence of d-orbitals in the "alence shell of nitro&en" !ismuth

(!i) also does not form pentahalides" #his is because due to inert-pair effect 5 oidation state of !i is not

stable"

ome general characteristics of the halides of Group 15 elements are described belo%"

Tr$)l$"e,% All the elements of Group 15 form trihalides (ecept N*0)"%a& All trihalides of Group 15 elements have pyramidal structure in the

gaseous state" *n all trihalides, the central atom sho%s sp0

hybridisation"

%b& 'cept !i70, all other trihalides are covalent" #he covalent character

of trihalides decreases in going do%n the group"

01'%'45%(As %e go do%n in the group, the tendency to form

ionic bonds increases" o, the covalent character decreases"

%c& #rihalides of Group 15 elements (ecept N70 and !i70) get easily

hydrolysed by %ater" N8l0 02/+ N20 028l+

5


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group" 8ondensed systems are formed by P 3 + 3 P lin6age or P 3 P lin6age" ome of the common

oo-acids of phosphorus are given belo%"

Ip'iC 3 log'i, %here'iis the acid dissociation constant for the release 2"

S!re'! o( O.o)#$", o( Group 15 Eleme!,

7ollo%ing generali.ations can help in predicting the strengths of the ooacids"

(i) #he strength and solubility of ooacids having central atom in the same oidation state follo% the

order, N J P J As J b

7or eample, for an oidation state of 5, the strengths of various acids of Group 15 elements

follo% the order, 2N+0J 20P+&J 20As+&J 20b+&(ii) 7or the ooacids involving the same element in different oidation states, the strength of an acid

depends upon the number of unhydrogenated oxygen atoms attached to the central atom" 7or eample, for

the ooacids of the type (+2)m K+n, the acid strength varies directly %ith the value of n" #hus, nitric acid

(2N+0) is stronger than nitrous acid (2N+/), i.e., 2N+0J 2N+/"

#he acids 20P+/, 20P+0 and 20P+&are approimately of eual strength, because all these acids

contain only one unhydrogenated oygen atom each"

#he strength of an acid is described in terms of acid dissociation constant ('a)" #he release of each

replaceable hydrogen in the acid molecule is characterised by the corresponding 'avalue"

Po,poru,A!om$# o% < 15 A!om$# ,*m7ol< P

A!om$# m),, < 01 u Ele#!ro$# #o($'ur)!$o< 1ssp0s0p0

Phosphorus is the second member of group 15 of the periodic table and has the electronic

configuration, 1s/ /s/ /p 0s/ 0p0" Although nitrogen and phosphorus belong to the same group, but theydiffer from each other considerably in their chemical behaviour"

#hite phosphorus ignites spontaneously in air. (o) phosphorus is always *ept under water.


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Allo!rope, o( Po,poru,Phosphorus eists in the follo%ing five different allotropic forms"

$!e or Dello: Po,poru,

=hite phosphorus is the most common allotropic form of phosphorus" *t is obtained by rapidly

cooling the vapours of phosphorus" *t is usually prepared either from phosphorite mineral or boneash" =hen

eposed to light, it becomes yello%"

%i& =hite (yello%) phosphorus is etremely reactive"

%ii& !elo% BBF8, its vapor density corresponds to the formula P&" Above 19BBF8, it eists as P/"%iii& ue to its lo% ignition temperature (L 0BF8), it catches fire spontaneously" ue to this reason, it

is stored under %ater"

%iv& *t is etremely poisonous"

%v& *t dissolves in carbon disulphide, and turpentine oil"

%vi& *t melts at &&"1F8 and boils at /BF8"

%vii& *t glo%s in the dar6 due to slo% oidation" #his phenomenon is called po,pore,#e#e%

Re" Po,poru,

Eed phosphorus is stable allotrope at room temperature"

Eed phosphorus is formed by heating %hite phosphorus in the

absence of air at about /5BF8" *t is not poisonous" *t is safe to

handle because it does not burn spontaneously at roomtemperature"

(i) *gnition temperature of red phosphorus is high (L

/5F8)"

(ii) *t sublimes on heating" *t melts at 1BF8 under

pressure giving yello% liuid, %hich on cooling gives %hite phosphorus"

(iii) *t is insoluble in carbon disulphide"

(iv) Eed phosphorus has a polymeric structure, (7ig" "1D)"

Bl)#; Po,poru,

!lac6 phosphorus is obtained by heating %hite phosphorus at about /BBF8 under very higher

pressure (about &BBB atmospheres)"

*t may also be obtained by heating %hite phosphorus at //B 3 09BF8 for days in the presence ofmercury"

(i) !lac6 phosphorus is crystalline in nature, and consists of a layered structure "

(ii) *t melts at 59F8"*t does not burn in air even upto &BBF8"

(iii) *t is a good conductor of electricity"

S#)rle! Po,poru,

8omparison of the properties of %hite and red phosphorus is made in #able "1/"

Po,p$e8 &P0+Phosphorus forms a number of hydrides" Phosphine (P20) is the most important hydride of

phosphorus" *t %as discovered by Gengembre in 190"

Prep)r)!$o

(i) *n the laboratory, phosphine is prepared by boiling %hite phosphorus %ith a concentrated solution

of sodium hydroide in an inert atmosphere of carbon dioide, oil gas or hydrogen"

P*,$#)l Proper!$e,

ome characteristic properties of phosphine are described belo%"

%i& *t is a colourless gas %ith disagreeable odour of rotten fish"

%ii& *t is highly poisonous in nature"

%iii& *t is only slightly soluble in %ater, the solution being neutral to%ards litmus"

%iv& *t condenses to a colourless liuid (b"p" 1 H), %hich free.es to a %hite solid (m"p" 10D"5 H)"

Cem$#)l Proper!$e,

ome important chemical properties of phosphine are given belo%"


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(i) B),$# )!ure% Phosphine is neutral to%ards litmus" !ut, it is feebly basic: it is a much %ea6er base than

ammonia" As a result, it reacts %ith halogen acids to give phosphonium salts"

7or eample, %ith 2*, it gives

(ii) $! )lo'e,% *t burns in chlorine giving phosphorus pentachloride"

:ii$+Re"u#$' proper!*% Phosphine acts as a strong reducing agent" *t eplodes in contact %ith a very

small amounts of oidising agent such as nitric acid, chlorine gas etc"

&$"+Form)!$o o( #oor"$)!$o #ompou",% Phosphine does not form any coordination compounds

%ith the transition-metal cations" 2o%ever, it forms coordinate compounds %ith electron deficient

compounds, e.g., %ith !8l0it gives,

U,e, o( Po,p$e

%i& *t is used for producing smo6e screens" 8alcium phosphide is used in smo6e screens" Phosphine

obtained catches fire to give the needed smo6e"

%ii& +n Holme$s signals" A miture of calcium carbide and calcium phosphide is ta6en in a container%hich is pierced and thro%n into the sea" Phosphine liberated catches fire and lights up acetylene"

!urning gases serve as a signal to the approaching ships"

Group 1 Eleme!,-I!ro"u#!$o#he elements +ygen (+), ulphur (), elenium (e), #ellurium (#e) and Polonium (Po) constitute

group 1 of the periodic table" #he first four members of this group are non-metallic in nature" #hese are

called #)l#o'e, (means ore-(orm$') because most of these metals occur in nature as oides, or

sulphides" #he last member of this family, i.e", polonium, is a radioactive element %ith a very short half-life"

Proper!$e, o( Group 1 Eleme!,

Ele#!ro$# Co($'ur)!$o#he group 1 elements contain si electrons in their outermost shell, i.e., these elements have si

valence electrons" All these elements have thes/p&valence-electron configuration

(i) A!om$# )" $o$# r)"$$

Atomic radius increases %hile moving from oygen to polonium" *t follo%s the order"

+ M M e M #e M Po

'PANA#*+N: #his is due to the addition of one ne% shell at each element do%n the group"

#he ionic radii of binegative ions (4/3) are bigger than the atomic radii of the corresponding

elements""

(ii) C)!e)!$o

#he self-lin6ing property of atoms %ith identical atoms is called catenation" +ygen sho%s a little

tendency to%ards catenation, e.g., in peroides, 3 + 3 + 3O/3"ulphur sho%s a strong tendency to%ards catenation, e.g., in polysulphides (n/3), sulphanes (2 3 n

3 2), polysulphuric acid (2+0"n"+02), and in various allotropes" #he 3 bond is very important in the

biological systems" #he 3 bonding is found in compounds such as, cysteine, some proteins and en.ymes"

#he catenation tendency decreases mar6edly as %e go do%n the group"

'PANA#*+N: #he catenation tendency decreases do%n the group due to the lo%ering of 4 3 4

bond energy in going do%n the group"

(iii) Ele#!ro )(($$!* &0ae+8 or Ele#!ro ')$ e!)lp* &E'+%#he energy change %hen an etra electron is added to an isolated gaseous atom is called electron affinity

(no% called electron gain enthalpy)" =hen the energy is liberated, the electron affinity is negative, %hile

%hen the energy is absorbed, it is positive" 'lectron affinity depends upon the si.e and effective nuclear

charge of the atom" #hus, the energy change (,) for the

reaction, is called the electron affinity of the element 4"

7or oygen and sulphur, energy is evolved %hen one electron is added to an atom of oygen and sulphur,

!ut, %hen second electron is added to the atoms of oygen and sulphur, large amount of energy is absorbed"


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#hus, the electron affinities for + Q +/3and Q /3are positive"

C)r)#!er$,!$#, o( ele#!ro )(($$!$e,% #he first electron affinity of oygen is much smaller than

those of the other elements"

'PANA#*+N: +ygen atom is the smallest of all the elements of this group" As a result, its

electron charge density is high" !ecause of this, the incoming electron eperiences greater repulsion than it

%ould eperience in the case of other elements of the group" #his leads to smaller value of its electron

affinity"

'lectron affinity becomes smaller as %e go do%n the group, i.e., from sulphur to tellurium"

'PANA#*+N: #his is due to the increase in the atomic radii %hile going do%n the group"

(iv) Ele#!roe')!$$!*

#he elements of group 1 are more electronegative than those of group 15" +ygen is the second

most electronegative element after fluorine"

'PANA#*+N: #his is due to increase in the effective nuclear charge %hile moving from group 15

to group 1"

'lectronegativity of group 1 elements decreases gradually from oygen (0"5) to polonium (/"B), i.e.,

electronegativity of group 1 follo%s the order,

+ J J e J #e J Po

'PANA#*+N: #his is due to the increase of the atomic radii in going do%n the group from + to

Po"(v) Io$,)!$o eer'* or Io$,)!$o e!)lp*8 I

#he ionisation energies of group 1 elements are uite high" ue to their high ioni.ation energies, it

is etremely difficult to remove electrons from the atoms of these elements"

'PANA#*+N: #he elements of group 1 are smaller in si.e and have high effective nuclear

charge" o, these elements have higher ionisation energies" !ecause of their higher ioni.ation energies, it is

very difficult to remove electron from the atoms of these elements" #herefore, elements of group 1 do not

form cations"

#he ionisation energy decreases as %e go from oygen to polonium"

'PANA#*+N: #his is due to an increase in the si.e of the atoms as %e go do%n the group"

#he first ionisation energies of lighter elements of group 1 (oygen family) are lo%er than those of

group 15, (nitrogen family)"

'PANA#*+N: +n the basis of effective nuclear charge, the ionisation energies of group 1

elements should be higher than those of group 15 elements" !ut, the first ionisation energies of +, , and e

are slightly lo%er than those of N, P, and As respectively" #his can be eplained in terms of the outer

electronic configurations of the corresponding elements of group 15 and group 1"

#he elements of group 15 have their p-orbitals in the valence shell, half-filled" 2alf-filled

configurations are more stable" ue to the etra-stability of the half-filled configurations more energy is

reuired to remove an electron from the outermost shell for the elements of group 15"

(vi) O.$")!$o ,!)!e,

#he outer electronic configuration of group 1 elements can be described as ns/np&" !eing strongly

electronegative, these elements complete their outer shells by gaining t%o electrons" #hus, all the elements

of group 1 sho% an oidation state of 3 /" 2o%ever, these elements also sho% other oidation states as

follo%s" +ygen sho%s an oidation state of / in 7/+, and 3 1 in peroides (+/ /3)" +ther elements of

group 1 ehibit oidation states of /, & and also" #he oidation states of & and being more

stable"

7or sulphur, selenium and tellurium, the oidation states of & and are important" #he & stateis more stable for e, #e and Po, than state" #his is due to the availability of d-orbitals in the valence

shells of the atoms of these elements" 7or sulphur the scheme is sho%n belo%"


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P*,$#)l Proper!$e, o( Group Eleme!, (i) P*,$#)l ,!)!e-At room temperature, oygen eists as a gas, %hile all other elements of group 1 are

solids"

(ii) 6e,$!*

ensity of Group 1 elements increases in going from oygen to polonium, i"e", the density of Group

1 elements follo%s the order,

+ M M e M #e M Po

'PANA#*+N: As %e go do%n the group, the strength of the van der =aals< forces acting bet%eenthe molecules increases" #his leads to a more cohesive structure" #herefore, the density increases as %e go

do%n from oygen to polonium"

(iii) Mole#ul)r ,!ru#!ure &or )!om$#$!*+

+ygen forms stable diatomic (+/) molecules, %hile sulphur,

selenium, tellurium and polonium are octatomic molecules, viz., ,

e, #eand Po %ith puc6ered-ring structures" #he puc6ered ring

structure of sulphur is sho%n in 7ig" "/1"

Rnder ordinary conditions, oygen eists as a gas, %hile all

other elements of this group are solids"

'PANA#*+N: #his is because oygen has a tendency

to formpS 3pS multiple bonds" o, oygen forms a diatomic (+ C +) molecule" ue to %ea6 van der =aals'PE #heory" #he structures of some of these compounds are sho%n belo%"

Group 1 Eleme!-I!ro"u#!$o

Group 1 of the periodic table accomodates si elements" #hese are, 2elium (2e), Neon (Ne), Argon

(Ar), Hrypton (Hr), enon (e) and Eadon (En)" #he last member, radon is a radioactive element"

#hese gases %ere earlier called inert gases, because of their chemical inertness (non-reactivity under

normal conditions)" #his chemical inertness %as attributed to their stable electronic configurations" *n the

last four decades, a good number of compounds of these elements have been prepared, thereby discarding

the earlier belief of their inertness" #hese gases, no%-a-days, are called noble gases (the gases %ith a little

chemical reactivity)" ince, these gases are present in or around the earth in very small amounts, these gases

are also called rare gases"

U,e, o( No7le G),e,#he main use of noble gases is due to their chemical inertness and lo% boiling points" All noble gases

find use in asers"

ses of elium

%i& *t is used in gas-cooled atomic reactors as a heat transfer gas"

%ii& *t is used for filling observation-balloons, due to its non-inflammability" *ts lifting po%er is D/;of hydrogen gas"

%iii& A miture of oygen and helium is used as a respiration miture by sea-divers" ince, helium

does not dissolve in blood, hence it does not cause a painful sensation called bends, %hen the

sea-diver comes out of %ater"


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ses of %eon

*t has moderately high electric discharge potential" *t has beautiful orange-red discharge colour and is

filled into electric discharge tubes used in decorations and for advertisements" #he colour so obtained in a

discharge tube depends upon"

%i& nature of gas or vapour mied %ith neon"

%ii& the type of glass used in the preparation of discharge tube"

ome typical colours given by neon-mitures are given belo%"

U,e, o( Ar'o

%i& *t is used in gas-filled electric lamps"

%ii& A miture of argon and mercury vapour is used in fluorescent tubes""

U,e, o( Kr*p!o

%i& *t is used for filling luminous sign tubes"

%ii& *t is used in filament lamps"U,e, o( Xeo

%i& *t is used for filling radio and television tubes"

U,e, o( R)"o

%i& *n the preparation of ointment for the treatment of cancer and other diseases"

%ii& Rsed in the scientific research on radioactivity

Proper!$e, o( Group 1 Eleme!,ome atomic properties of Group 1 elements are described belo%"

Ele#!ro$# Co($'ur)!$o

All the elements (ecept 2e) have outermost electronic configuration of ns

/

np

" 2elium has t%oelectrons in its first and its only shell (1s/)"

ince, all the available orbitals are completely filled, hence noble gases are relatively nonreactive in

nature" #hese elements sho% limited reactivity only under drastic conditions %ith oygen and fluorine"

&i+ A!om$# r)"$u,

7or noble gases, the atomic radii are in fact van der =aals< radii" #he atomic si.e of the noble gas

elements are bigger than those of the corresponding Group 19 elements" #he atomic radius increases

regularly in going from helium to radon"

'PANA#*+N: *ncrease in the atomic radii as %e go do%n the group is due to the addition of a

ne% shell %ith each element in going do%n the group"

(ii) Io$,)!$o eer'*

*onisation energies (no% called ionisation enthalpy) of noble gases are very high, even higher thanthose of the elements of group 19" #he ionisation energies decrease do%n the group as the si.e increases

from helium to radon" #he ionisation energies follo% the order,

2e J Ne J Ar J Hr J e J En

#hus, it is easier to remove electron(s)from xenon than helium"

(iii) Ele#!ro )(($$!$e,

#he electron affinities (no% called electron gain enthalpy) of noble gas elements are almost .ero"

#his is because all the shells of noble gas atoms are completely filled and therefore, cannot accept any

additional electron"

P*,$#)l Proper!$e, o( Group1 Eleme!,(i) P*,$#)l ,!)!e


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(iv) L$ue()#!$o !e"e#*

Noble gases have very little tendency to%ards liuefaction" #herefore, these gases are difficult to

liuefy" #he liuefaction tendency, ho%ever, increases in going do%n the group"

'PANA#*+N: #he atoms of noble gases interact %ith other atoms very feebly due to %ea6 van

der =aals< forces bet%een them" #he strength of van der =aals< forces increases as %e go do%n the group"

o, heavier elements of this group sho% greater tendency to%ards liuefaction"

(vi) Mel!$' )" 7o$l$' po$!,

he meltin& and boilin& points of noble &ases are e


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S!ru#!ure )" 7o"$'% e7/is a linear molecule, 7 3 e 3 7" >alence bond repre-sentation of e7 /may

be eplained, if one of the 5p electrons is promoted to the 5d orbital"

Xeo !e!r)(luor$"e8 &XeF2+

*n this compound, enon ehibits an oidation state of &"

Prep)r)!$o% e7&is obtained in good amounts by heating a miture of enon and fluorine in the

molar ratio 1 : 5 at &BBF8 and 5 3 atmosphere pressure in an enclosed nic6el vessel for a fe% hours"

%i& 4t reacts "iolently $ith $ater"

0XeF24 O Xe 4 XeO04 1F 4 0/ OS!ru#!ure )" 7o"$'

e7&is a planar molecule" >alence bond representation of e7&may be eplained if, t%o electronsfrom 5p orbitals are promoted to 5d orbital"

+ne 5s, three 5p and t%o 5d atomic orbitals of enon hybridi.e to give si sp0d/hybridi.ed orbitals"

#he four singly occupied hybridi.ed orbitals are used by four fluorine atoms for bond formation and the rest

t%o are occupied by lone pairs as sho%n in 7ig" "&5"

Xeo e.)(luor$"e8 &XeF+enon ehibits oidation state in this compound"

Proper!$e,%

*t is a %hite solid, %hich sublimes at room temperature" *t melts at

&D"5F8 to give yello% liuid"

%i& *t undergoes hydrolysis even due to moisture in atmosphere to give

solid e+0"

XeF4 0O XeO04 F

S!ru#!ure o( XeF#he e%is structure of e7is given in 7ig" "&"

Xeo !r$o.$"e8 &XeO0+

(i) B* !e *"rol*,$, o( .eo (luor$"e,% e7&and e7on hydrolysis gives e+0"

e7 02/+ Q e+0 27


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e7& 1/2/+ Q /e+0 &e 0+/ /&27

%i& "

e+0 2/+ Q 2/e+&l 2 2e+&3enic acid

S!ru#!ure o( XeO0*n e+0, e ehibitssp

0hybridisation" +ne of the hybrid orbitals is occupied by a lone pair, %hile

other three are involved in the bond formation" #his leads to a trigonal pyramidal structure of e+ 0"

Xeo o.*!e!r)(luor$"e8 &XeOF2+Prep)r)!$o%

enon oytetrafluoride (e+7&) can be obtained by partial hydrolysis of e7"

e7 2/+ Q e+7& /27enonoytetrafluoride

S!ru#!ure%

*n this compound, enon ehibits oidation state and sp0d/hybridisation" #his gives suare

pyramidal structure for e+7&"

Documents

1. Basic Concepts P-block Class 12