Class xi p block elements chapter 11

Notes

1. $ P-BLOCK ELEMENTS

Group number= 1310 18

General Configuration= ns! np'*

3 eroup 18

Group oxidation state (most common oxidation state: group 1:

INERT PAIR EFFECT: In 8, C and N amis, the group oxidation state if the most stable
Orion state for ightercloments inthe group. However, the oxidation state two les thon
the group oxidation state becomes progressively more stable forthe heavier elements in each
om. The occurrence of oxidation sates two less than the group oxidation state forthe
Feeder elements in a group is known as INERT PAIR EFFECT. is the reluctance of -letrons
- pe B AL ha In TL
da Bo aA H
Rosson: Down the group Se increases, poor shielding effect of d and feecrons increases
which Increase the attraction of s-eletrons of valence shall towards the nucleus and donot
dtow them o paniciate nbonó formation. gpl © Sc Gx Sw fb
440-0442
HW

to participate in bond formation

ANon-metsls and metallids exist ont in pblock,
"Non-metallic character decreasés down the group and increases across the period.

Non-metals have high ionization enthalpy and form anions while metals have low fonieation
enthalpies and form cations. Non-metals form covalent compounds with non-metals due to
small electronegatvity-difference while they form lonic compounds with metals due to high
electronegativity difference.

-Non-metals form acidic and neutral oxides while metals form basic and amphoteric oxides,

First member of p-block group differ from the remaining members of their corresponding
group in two major respects: first member has small sie and absence of é-orbital (has no
tendency to extend its valence shell. Consequences: a) [BF ion is formed by boron
vie aluminium forms [AE because boron has small ire and absence of doit Henee it
‘cannot accommodate more than four atoms of fluorine in its valency shell wile aluminium can
‘accommodate more than four atoms of fluorine as it has large size and presence of vacant de
“orbitals, b) The combined effect of size and availabilty of d-rbitals influence the ability to
form pi-bonds. The first member of group can form prepit multiple bonds to itself (u.
Cac, C20, CEN, NEN, N-O) and to other second row elements. This type of pbonding is not
particularly strong for heavier p-block elements. Heavier elements donot form pr-prt multiple
‘bonds but they can form less stable predn multiple bonds as they have presence of vacant de

2. orbitals.” e) Coordination number in species of heavier elements may be higher than for the
first element in same oxidation state. Eg, NO; and POS”

“GROUP 13= 8,A, Ga,in,71

Occurrence- Boron= Orthoboric acd (Hs80s], Borax (N9:8,0;.10H,0). Tw isotopes of boranz
8-10 (19%), 6-12 (62%). Aluminium= most abundant metal and third most abundant element
on carth’s crust. Bauxite (Al, 21), erolite (NayAlsl. Ga, In, Tl ess abundant elements,
{0-10%s used to absorb neutrons in nuclear reactors).

Yon-metal but ALGA. I= metal

Properties: 1) Configuration=nsinpt

2) Size increases down the group due to increase In no. of shell, Deviation: atomie size of
“Goliur i fess than Al due to the presence of additional 10 d-electrons offer poor screening
effet for outermost electrons from increased nuclear charge in Go

3) lonsation enthalpy- decreases down the group but not smoothly. Decrease from B to Als
associated with increase in size but observed discontinuity between IEs of Al and Ga, and
between In and TI are due to inability of d and f-lectrons, which have low screening effec, to
‘compensate the increase in nuclear charge.

4181s non-metallic in nature and hard and black coloured solid 8 has high melting point due to
its vey strong erystaline lattice. Rest of the members are soft metal with low melting point.
Ga has very low melting point (303K) and very high boiling point (2676). Hence, Ga is used for
measuring high temperature.

Chemical Properties. 1) mert Pair effect

2) Boron can readily form covalent compounds unlike other elements in the group. As boron
cannot form 8? ion. The total energy needed to form 8" ion is much greater than
compensated by ttice energies (in solids) or hydrtion energies (in aqueous solutions. Hence,
boron behave as non-metal

3) Formation of halides: Mi (rihalide) Eg. BF; Halides of boron are covalagt and monomeric
in vapour phase: sp2 hybridsation = trigonal planar structure Vacambp-

3. All tialides of group 13 behave as lewis acids. In tivalent state, the no, of electrons around
central atom in a molecule of these compounds are only six Le. they are electron deficient
‘molecules. They have tendency to accept a pair of electrons to achieve stable configuration. The
tendency to behave lewis acd decreases with increase in size of central atom down the group

ain decreases, Terre, order Lui acid nth: we
BU, 7 ALU, > Gals > Ence > TLL fre)

„BCl easily accepts alone ale of eletrons from ammonia to form BCh Na

a boron halides, order of lewis acid strength: Bl, > BBF,> Ch. > BF. BF, should be most
acidic due to the presence of electronegative fluorine. But its least acidic. This order can be
easily explained on the basis of tendency of halogen atom for back donation of its lane par of
elections to the empty p-orbital of B atom through pr-pm bonding. Since the sie of vacant 2p-
orbital of 8 and 2p-orbial of containing a lone pair electrons are identical, therefore, the lone
pair of electrons on fis donated towards the B atom. Hence, electron deficiency of 8 decreases
and thus BF isthe weakest lewis acid

As the se of halogen atom increases down the group from Ct I, the extent of ovrlap
between 2porbital and bigger proba of halogen [Bi CI, 4p in Br, Sp in 1) decreases and
therefore, electron deficiency of increases and lewis ald strength increases from BF to Bo

=» BG 43.0 —> 1,80, + 3nF

Boric acido u N
> 86 +40 (und —> Caco] sp

> NE an DAN + ES oat

tn lt ot Sta tht mL Des os va he Gotas
are malablo with land ther element, he maximum ovalence more than 4. They so et
dimerited trough the halogen brig, The metal species completes its octet by accepting
electrons from halogen. ACh forms A

4) Reactivity towards alr- In crystaline form, Bis unreactive, Amorphous B and Al mtal react,
thai on heating to form 8,0, and ALO» (protective layer advantage of corrosion.

um+.30, 222,03 k 2M +N, —> 2 MN (A)
2,0 N: 09503 md Th?

aride 5 ae:

e

4. el

Pampero ehaviorof AyOsandale 2AL + GHL—> 2 ALU + 341

2AL+ Naot + 6 HD —> ana (at Con] +37

Sodium urabydeensalumunatsli)
5) Anomalous behavior of B- a) Baron is non-metal while other members of group 13 are

metals. _b) Boron forms covalent compounds while others form ionic compounds. c) 8
‘exists in two allotropic forms ie. amorphous and crystalline form while others donot show
allotropy. d)B shows maximum covalency of 4 while others show upto 6: e) Boron oxides and
hydroxides are acidic while others oxide and hydroxides ae e

6 Similarity of boron with silicon-(Oiagonal Relationship) 2) Bath 8 and Si are non-metals nd
have high melting points. b) Both 8 and SI exhibit allotropy. c) The oxides of both 8 and Si are
‘weakly acidic in nature. d) Bath and Si form large no. of hydries.

8,0, + 2N40 —> > Nago, + H,0
Coda

G60, + 2NAOH — Nat + 1,0 on
Solier nibicali a
‘SOME IMPORTANT COMPOUNDS OF BORON: ho— ie A, Son

—

IS

a ver masse nt para DO]
ore formula =Na (0.004) 81:0 bn

Na, By, HO — > 2N00H + Y H3B03 (petheboric au)

Dorax Bead tent
> [5 —5 2NaBo, + B,0,

Na, B40," loo > Na, BD, labo, + 830,

On heating bora fist loses water molecules and swel up. On further heating it tums Into à

transparent iid, which sli ino gas Ike matral known as borax bead. Metaborats of

many transition metas have characteristic colours and therefore, borax Bead test can be used

to enti them in abs. Eg, CO(BO, bed formed Is blue coloured

2) Orthoborie acid #580, or B(OH}, «White crystalline so soapy touch = sparingly soluble
in water- highly soluble in hot water. Preparation-

(ay NA, By0, + 2HUL + 5H,0 —> oNah + YH 803

6) BB + 30 —> 1,803 + 3HF
Structure: t has 2 layer structure containing planar BO, units joined by HHvonds. Bori acd is
weak monobasic aid is a lewis acid by accepting electrons ftom a hydroxyl on and cannot
release H'ions ont own,

5. Pese ib a
wrtale ewnanpbasio aud as — 7 SA
B(0), +240 — [Blo] + Hot

7 a ö
25 Heo,—> 8,0,
19803 ax, MBO © “oy
“Ho \ 1
LEA Hobo

A I
Uses: Bori acid is used in the manufacture of boraslicate glass and as a preservativo for milk
and foodstulls

3) Boron hydrides- (Compounds of Band H) Ba. Balls

DIBORANE: Preparationof By Hy

OB + BLALHY —> 28% + SUF +3AL6

D) 28H +2 —> Ba + 2NAT +H

fe) 28% +g0aH 50% By +6Nar

Structure of iborane: it consists ol terminal Matams and 2 Batoms le in ne plane, Above

and below this plane, there are two bridging H-atoms containing 3-centred 2. leet
or banana bands,

B= Is 26h ap!

sh a ar a
24H BH ES 2 Bd 6 ey
bnahednal ma

NaBH and UibH~ are good reducing agents

6. -Diborane Is colourless and highly tox gas and catches fire spontaneously upon exposure to

ar. BS He +30, —B, 0,420 N
Boric. Msg Sert
Falk + mo — 2-8 (0), #640 A k
Bye + NC), —> BH N(CH, SPAN

MESS
an +20 — %28m:CO +
By He + 20 —> Byte an, om BH. (NHS), TH)

effect)

Occurrence: C 27" most abundant element as coal, graphite and diamond. Isotopes of
carbon are- C12, C-13, C-14 (C-14 is used for carbon dating), Si= as slates, SiO (sand)-used
in glass, coment. Si and Ge are used in semi-conductors and transistors, Sn= Sn; (Cassiterie),
Pb= POS (galena)

Covalent radius: increases from Cto Si and then only small increase is observed from Sito Pb
ue to presence of d- and f- electrons in heavier elements

lonisation Enthalpy- Fist IE of group 14 is higher than IE of group 13 due to decrease in size
across the period. IE decreases down the group . Small decrease from Sito Ge to Sn and slight
increase from Sn to Pb due to poor shielding effect of and f-electrons and increase in size of
an atom.

Physical Properties. All menibers are solls. Cand Si are nor-metals, Ge is a metalloid, Sn and
Po are soft metals.

Chemical Properties 1) Cannot exceed its covalence more than 4 due 10 absence of d'arbital
‘while other members form complexes lke SiF6", GeCl” {sp'd' and show covalence upto 6

2) Reactivity towards oxygen- Form monoxide and dioxide (MO and MOS) SiO exists at high
‘temperature. ce EB, GeO, , Sn, , Pbo,
2) Reactiviy towards water, +
5
Gut > ED, + HH

nd Ge are not affected by water

7. Pb is unaffected by water due tothe formation of protective oxide film POO,

A Reactivity towards halogens: (MX, and MI) MX. is covalent and sp? wbriised but Safe
and Pb are ion. PbFA doesnot exist due to inert par effect, it only shows +2 oxidation state.
Gex is more stable than GeX).

Hydrolysis: Cl cannot be hydrolysed as Chas no vacant dorbital and has very small sie So, i
cannot accomodate the lone pair of electrons from oxygen atom to water molecule. SIC can

Be hydroysed a
Bucs

H
Dome f
ut, TA gp were
a ce ul

Le + yA
aa wen
a

Site” known whereas SICH? is not known because- a) 6 large chlorine ions cannot be
‘accommodated around Si” due to its limited size. b) Interaction between fone pair of CI and
iis not very strong,

Important trends and anomalous behavior of carbon- € diles from rest of members of fs
troup due to its small sie; higher electronegativity, higher IE and unavailability of d-orbitals.

‘Anomalous behavior of C- 1) C shows maximum covalence to four while other members can
‘expand theircovalence due to presence of d'orbitals

2) Carbon can form pr-pr multiple bonds with itself (0 NO) and to
other second row elements of small sie, Heavier elements donot form pr «pr. bonds because
their atomic orbitals are too large and diffuse to have effective overlapping, they form pn „or
bonds

3) C atoms have the tendency to link with one another through covalent bond to form chains
and rings. This property is known as catenation. This Is because C-C bonds are very strong.
‘Down the group sie, electronegativty decreases and catenation tendency decreases: € >> Si>
Ge =Sn.(Pb=no catenatlon) Si bonds are weak. So, Si shows less catenation.

Allotropes of carbon —

1) Diamond-it has a crystalline lathe sp? hybridisation of C atom and each € atom s linked to
four other C atoms 3-4 riid structure. Directional covalent bonds are present throughout the
lattice Its hardest substance and has high melting point. Used as an abrasive for sharpening
hard tools, laments for electric ight bulbs.

2) Graphite: thas layered structure held by vander waals forces and consists of planar
hexagonal rings of carbon having sp? hybridised C atoms. Each carbon atom is attached to 3 C

8. atoms electron forms n_bond,(Thermodynamically most stable). + Due to presence of free
eletrons, graphite conducts electricity. is soft and slippery and hence is used asa lubricant in
machines at high temperature.

3) Fullerenes: discovered by Kroto ,Smally and Curl in 1985. They are made by heating of
‘graphite In a presence of inert gases Ike Ho or Ar. They contain C-60 and C-70 molecules and
upto 350. They are only the pure form of carbon as they have smooth and are cage ike
molecules 60 has soccer ball shape and is known as buck minister fullerene. It contains 20x.
‘membered rings and 12 five membered rings. AC atoms have sp hybridisation.

(Others form of elemental C are carbon black, coal, coke and charcoabimpure forms of graphite
and fllerenes.

(Carbon black: obtained by incomplete combustion of hydrocarbons.
Charcoal coke from destructive distilalon of wood or coal

Uses of carbon-1) Being good conductor, graphite Is used for electrodes in batteries and
electrolysis

2) Crucibles made from graphite are inert to dilute acids and alkalies.

3) Activated charcoal is used in tropping polsonous gases, in water filters 10 remove
contamination and in acto control dour as itis highly porous

1) Carbon black is used as black pigment in black ink and a flor in automobile,
‚Some important compounds of carbon and licon-
1] Oxides of carbon- a) Carbon monoxide

[5
Preparation: incomplete combustinofC- D.C + D —> 260
ane Sy

0 oot ae Ot Lo

A) On commercial ele: COs prepared by passage of steam over ht coke oe
cf) + ho ® CE cop q ay Cs y)
20470 +4N, TR 20+ IN GY [producer gat]

CO) Colourles, odourless, insoluble in water. Its a powerful reducing agent and is used in
extraction of many metals

Fe 0 LD + 300% > 2R(9+ 300,49)
AOÛ + (0G) > zn) + C0)

9. w

in CO, 620%) there are one sigma and2 pi bonds between C and O. Because of the presence
of lone pair on €, CO molecule acts a6 donor and reacts with certain metals to form metal
carbonyls. £g-FelCOs.

in] CO is highly poisonous as it has high affinity towards haemoglobin more than oxygen (300
times) and forms carboxyhaemoglobin.t prevents oxygen transportation in the body and lead
to death

bi carbondionde- Preparation: 1) By complete combustion uf Cand € containing ues
C+0, —> CO,
Cry lp RO A> Co, P +20)

m OC, + HU > (ag + Core

wconmercl arent: Calo, Log (0 HL

ti colors, odoules gas, less soluble in water
Co, + HO —> HCO, ( Came, oid)

Carbonic, acid ib vay tado dibasic, Avid —

HO + 40 == Hs + Ho?

HOS +0 == Cor + Mor

COL NEO; buffer sy Tem lps to maintain pl of blood between 7:26 1 7.42

4, 2Na0H — Na, (O, +210
ra ag TE

san atmosphere, percentage of CO, by volume + 0.03%. 1 is removed by photosynt
converted into carbohydrates by plants.

i and

‚increase in CD, content in atmosphere lead L increase in green house effect and raise the
temperature of earth's atmosphere.

(COs in the sold form exist as dry ice by allowing the liquefied COs to expand quickly

Uses: i) Dry ice is used as a refrigerant for ie-cream and frozen food. 1) CO; (gh is used to
carbonate soft drinks, i Its used in fire extinguishers as its a aon-supporter of combustion,

“Structure of CO: = sphybridised € by forming prepr bonding with O atoms ~ has linear
‘geometry. It has zero

10. SiO: Sila) 95% of earth's erst is made up of sce and sileates. Quartz, Cristobal and
Kridymit are some of the crystalline forms of sica and are interconvertibie.

Structure of Si) —Itis covalent, 3-D network solid in which each Si atom to four oxygen atoms
in tetrahedral manner and each oxygen atomsin tetrahedral manner and each oxygen stoms in
tetrahedral manner and each oxygen atom in tur is bonded to another Si atoms forming eight

membered rings containing pre bonds. ob

“sea lsatmstnn-reahr because ofveryhignsiObondenttaby. D D do

Gi, + 2Na0H —> Na, S10, HO i
pie

GO, +YHF —> SA +2H,0 d
Uses: a) Quartz is used as piezoelectric material in clocks, radio and television broadcasting, DJ
ca gels used in chromatography,

RR A i - dichiotilane,
Lots Ge (img .)

Dimethyidiclorostane on further hydrolyse followed by polymerization form straight chain
icone polymers.

au, Zr Ces On.

bo qe
&

i pa

noi o A E ia
Ut mi u Matalin m
ee ct
My), WR > rs on)
€, fee CH), (08) es qa

qa EN
Ho-& 0H + Ho-G— or eee. —0 op an Oh
ny by fiyymucivaion CA CN (Giegre)
“Properties: 1) Sicones are water repeling as they contain many alo roups. i) They are
Thermally sable, have high dielectric constant, ii) They are resistant to oxidation and

chemicals

Uses: Used as grease, sealant, electrical insulators and for making water proof fabrics.

11. 1) Slicatos» E Zeolites, Mica, Asbestos. Basi structural unit of slates is SiO," in which
silicon atom is bonded to four oxygen atoms in tetrahedron fashion. Slicates may present as
discreto units or are joined together from corners by sharing 12,3 or 4 oxygen atoms per
silicate units forming chan, ring, sheet or 3-0 structure, Negative charge on slicae structure is
neutralized by positive charge metal ions. Two man-made silicates= Glass and Cement

0.
\ ie
a % wy so / iN e
Qs > Dog
4 eoltes Tey ore known as oluminsliats as feu tion atoms are replaced y aluminium

atoms in 3-0 structure of iO; and acquires negative charge balanced by cations ike Na", K oF
Cog, of aluminoslicates are feldspar and zeolites.

Zeolites have honeycomb like porous structure. Its also known as shape selective catalyst Its
used as catalyst in petrochemical Industries. &- 25M-S is used to convert alcohol into petrol
Hydrated zeolites are used as ion exchangers in softening hard water.

Other important reactions:

) Ba +39 —> BH), Fame

2) Cty +H,0 (bem) — Cove, + 2H
proc Choiorout Pp

3) 885 + 64 — Bulk + EL BR,

Y B&M HE — Bl, + 610

DIENTE DM O, ito ati bolo)
6) 1,80, ees HO, + HE