p-Block

BORON FAMILY ................................................................ Page 2 - 10

CARBON FAMILY .............................................................. Page 11 - 17

NITROGEN FAMILY ......................................................... Page 18 - 27

OXYGEN FAMILY .............................................................. Page 28 - 37

HALOGEN FAMILY ........................................................... Page 38- 47

INERT GAS FAMILY ......................................................... Page 48 - 50

SOLVED EXAMPLES ........................................................ Page 51 - 55

EXERCISE–I ...................................................................... Page 56 - 67

EXERCISE–II ..................................................................... Page 68 - 78

EXERCISE–III ................................................................... Page 79 - 83

ANSWER KEY .................................................................... Page 84-85

 Element Atomic no. Outer shell configuration
B 5 He 2s2 2p1
Al 13 Ne 3s2 3p1
Ga 31 Ar 3d104s24p1
In 49 Kr 4d105s25p1
Tl 81 Xe 4f145d106s2 6p1
x GENERAL POINTS
(a) Penultimate shell of Tl has 18e¯
(b) Anti penultimate shell of Tl has 32e¯
(c) Ga, In, Tl has 18e¯ in penultimate shell.
(d) (7.4%) Al the third most [Ist O2 (46.6%), 2nd Si : (27.7%) abudant element in the earth crust and
is the most abundant metal
x GENERAL PROPERTIES
(i) Nature
(a) Boron is a non metal. Boron atoms has covalent bond in its polymer.
(b) Al, & Ga reacts both with acid & bases and gives H2 gas in the reaction and so are called
amphoteric metals.
(ii) Atomic Radius & Ionic Radii : p Increases
(iii) Density : p Increases
(iv) Melting and Boiling points :
(a) B has very high melting point & boiling point due to polymer.
(b) Generally p Decreases
but B.pt B > Al > In > Tl > Ga
M.pt B > Al > Ga < In < Tl
(c) Ga has least melting point. among all these.
(d) Ga exist in liquid state.
(e) Ga is the only element in periodic table which can exist in liquid state over large range of temp.
(f) Main use of Ga in high temp thermometer.
(v) Ionisation Potential :
(a) Depends on size
Generally p I.P. (decreases)
Exception In < Tl
Due to size difference and nuclear attraction is more in case of Tl.
(vi) Electronegativity : p E.N. (decreases)
(vii) Oxidation sate :
ns2 np1 o ns1 npx1 npy1 npz0
G.S. E.S.
(a) Only covalent bonds are formed valency = 3 & oxidation state = 3±
(b) Compounds are formed by sp2 hybridisation and have trigonal planar geometry.
(c) Compounds of B are more covalent than compound of Al because charge/size ratio of B is more
than Al.
(d) The charge density of B is more because polarising power of B is more
 more covalent character.
(e) B o T" Covalent character decreases due to decrease in charge density or polarising power.
Boron Family [2]
 (f) Trivalent compounds of IIIrd group are electron deficient
Eg. BF3 acts as a lewis acid.
(g) In general B shows oxidation state of + 3 and – 3
Eg. Mg3 B2 the oxidation state of B is - 3.
(h) 6s e¯ of T" {Inert pair effect} are same as duplet configuration of He and so 6s e¯ are inert and
does not take part in chemical reaction.
(i) T" has valency = 1, 3 & oxidation state = + 1 & + 3.
(j) T"+3 is strong oxidising agent.
(k) T"+3 is highly unstable.
(l) Ga & In has trivalent compounds more stable.
(m) T"+ Compounds resemble compounds of alkali metals
Thallous T"+1 compounds will be more stable as compared to Tallic compounds (T"+3)
(n) Ga, In, T" show inert pair effect in their compounds.

x Extraction of Boron
Extraction from minerals :
Principle ŸBoron may be obtained by treating borax with hot concentrated HCl igniting the boric
acid H3BO3 to give the oxide B2O3 and finally reduced with Mg.
Na CO Hot and Mg
Ca or Mg 23 o Borax Conc
 o H BO ignited
. HCl 3 3  o B2O3 Heat
o B

2Ca2B6O11 + 3Na2CO3 + H2O ŸŸ 3Na2B4O7 + 3CaCO3  + Ca(OH)2

Colemanite
Na2B4O7 + 2HCl ŸŸ 2NaCl + H2B4O7
Borax
H2B 4O7 + 5H2O ŸŸ 4H3BO 3
2H 3BO 3 ŸŸ B2O3 + 3H 2O
B2O3 + 3Mg ŸŸ 2B + 3MgO
x CHEMICAL PROPERTIES
Formation of Halides :
(a) Halides formed have formula MX3 & MX.
(b) Halides of B are MX3 Halides
ie BF3, BCl3, BBr3, BI3.
(c) MX3 halides of Ga & In are more stable while MX halides of Tl is more stable.
(d) Ga & In Halides are more Ionic than Al one.
(e) BCl3 o TlCl the rate of hydrolysis decreases because size increases so less is the ionic character
more is the hydrolysis
BCl3
p Ionic character (Increases) so hydrolysis decreases
Tl
H2O
(f) TlCl  o No reaction.
TlCl will dissolve in H2O but will not undergo hydrolysis.
(g) AlCl3 to TlCl Charge density decreases. So polarising power decreases & Ionic character
increases.

Boron Family [3]

 (h) On BF3 o 9 lone pairs are available

(i) Acidic order BF3 < BCl3 < BBr3 < BI3.
(j) In BF3, B has vacant 2p orbital and 2p orbital of F has lone pairs of e¯. The vacant 2p orbital of
B overlaps 2p orbitals of F containing lone pairs e¯. This result in formation of a weak bond
which is called as back bonding.
(k) Due to back bonding, the availability of vacant 2p orbital on boron of BF3 decreases. so it acts
as a weak lewis acid.
(l) From BF3 to BI3. the tendency to undergo back bonding decreases so there will be greater
availability of vacant 2p orbital on Boron and hence the lewis acid character increases.
(m) Al2Cl6 (Aluminium chloride) :- Exist as a dimer.

Above 700°C Al2Cl6 converts to AlCl3.

(n) Al2O3 on heating with coke & Cl2 forms Al2Cl6 and this reaction is called as Reductive
Chlorination.
Al2O3 + 3C + 3Cl2 o Al2Cl6 + 3CO.
(o) BF3 do not form dimer while other forms because, the energy released by the formation of an
additional bond to another boron atom is not sufficient to compensate for the loss in energy to
the system in overcorning the B-F pS-pS bonding in the monomer itself.

mo mo

(p) Al, Ga, In & Tl do not show back bonding because of increase in the size of the element.
Actually they make use of vacant p-orbitals to complete their octet by forming dimers.
x Formation of oxides
(a) Oxides formed are mainly of two types
(A) M2O 3 (B) M2O
B2 O 3 Tl2O
Al2O3
Ga2O3
In2O3

(b) Tl2O3 at 100°C forms Tl2O because Tl2O3 is strong oxidising so decompose into Tl2O, while
B2O3& others will not go change on 100°C.
Tl2O3 ' o Tl2O + O2

(c) Al2O3 is amphoteric oxide as it is dissolved in H2O and neutralising same is with Ga.

(d) Al2O3 has high melting point & does not fuse easily.

Boron Family [4]

 (e) Oxides and Hydroxides gradually change from acidic to basic character through amphoteric
(Gallium oxide and Gallic hydroxides). On moving down the group.
HCl
So when Tl2O  o TlCl + H2O
This reaction confirms that Tl2O is basic.
(f) Al2O3 has very high melting point & it can with stand very high temp & so it is used in the form
of Refractory lining for furnaces.
(g) B2O3 is a weak acid due to when
B2O3 + H2O o B–O–H
B m O m H, B is in +ve oxidation state and it is electronegative and an element which has both above
conditions, withdraw e¯ from O & O will withdraw e¯ from H and so the strength of bond between O
& H become weak & so in aqueous medium B2O3 releases H+ ion form B – O – H and so behaves as
a weak Acid.
x Formation of Hydrades :
(a) Boron Hydrides are called Boranes and has general formula as BnHn+4 & BnHn+6
(dihydroboranes).
Eg. B2H6 diborane while B4H10 o dihydroxy tetra borane.
B5H9 Pentaborane while B5H11 dihydroxy pentaborane.

(b) Q. 1/2 mole of diborane on hydrolysis released ....... moles of H2.

Ans. 3 moles.
B2H6 + 6H2O o 2H3BO3 + 6H2but in Q. i.e. 1/2 mole instead of 1 mole.
Note : As much hydrogen will be in hydraides it will gives that much amount of H2 on hydrolysis.
(c) B2H6 to TlH the stability decreases because size of Tl ion be large and in the lattice of Tl ion
there will be maximum repulsion. So least stable. (Ac. to Fajan's Rule.)

(d) The Hydraides of IIIrd group combined with also act as strong reducing agents.
Eq. LiAlH4 or NaBH4.
LiAlH4 o Li+ + AlH4¯
x FAMILY MEMBERS OF “BORON FAMILY”
Boron :
Compounds of Boron :
(a) Borax i.e. Na2 B4O7. 10H2O : or Tincal :
(i) It is also named as sodium tetra borate decahydrate.
(ii) Common Indian name is Suhaga.
(iii) Na2B4O7. 5H2O is known as Jeweller's
Boron. - also named as sod.tetra borate penta hydrate.
(iv) Na2B4O7 is known as Boron glass
(b) Preparation :
Form colemanite :
Ca2B6O11 + 2Na2CO3 ' o 2CaCO3 + Na2B4O7 + 2NaBO2
Both these are fused together.
Both Na2B4O7 and NaBO2 are solid & soluble in water and so both these are separated by crystallisation.
{which involves heating of solution & then slow cooling}
When crystallisation is done, less soluble, one is first obtained and so Na2B4O7 will first obtained and so
Na2B4O7 will first appear as crystals & then NaBO2.

Boron Family [5]

Note: (i) If crystallisation is done below 60°C then ordinary Borane is formed. (Decahydrated).
(ii) Above 60°C jeweller's Borane will be obtained. i.e. Na2B4O7 5H2O.
(iii) Anhydrous Borane will never be precipitated from the aqueous solution.
(c) Chemical Properties :
Action of Heat on Borane :
(i) Borane swells up on heating.
(ii) On heating borax loses water and swells into a white mass which on further heating melts to
forms transparent glassy solid called Borax glass and Borax bead.
Na2B4O7.10H2O  740 $ C
o Na2B4O7 
Heat
o Na2O + 2B2O3.

(iii) The borax bead is due to the formation of B2O3 which when fused with metal salts form
corresponding metaborate.
B2O3 + CuO o Cu(BO2)2
Copper meta borate (Blue)
(iv) Colour of meta borates
Cu Fe Co Ni Cr
Blue Green Blue Brown Green

DIBORANE (B2H6) : It exits in gaseous state & is highly inflammable in air and poisonous.
(a) Method of preparation :
(i) By LiAlH4 :
4 BCl3 + 3LiAlH4 o 3AlCl3 + 3LiCl + 2B2H6
(ii) Industrially it is obtained by reduction of boron trifluoride with sodium hydride.
2BF3 + 6NaH o B2H6 + 6NaF
x Properties :
(a) Action of Air : Reaction is highly exothermic and due to high evolution of energy it can be
employed as industrial fuel not domestic because it is poisonous
B2H6 + 3O2 o B2O3 + 3H2O 'H = - 2165 kJ/mol

(b) Stability : It is stable only at low temperature when heated between 100°C to 250°C, it
changes to a number of higher hydraides.

(c) Hydrolysis :
B2H6 + 6H2O o 2H3BO3 + 6H2

(d) Reaction with alkali : Form meta borates

B2H6 + 2NaOH o 2NaBO2 + 6H2.

(e) Chlorination :
B2H6 + 4HCl o B2H2Cl4 + 4H2.

This formation of B2H2Cl4 show that the 2H left in B2H2Cl4 are responsible for dimer formation (Bridge
H). Diborane has only four replacable H and with their replacement, the dimeric structure continuous to
be as such. Remaining 2 hydrogen when they get deplaced, the dimeric structure breaks indicating that
these two hydrogens are acting as bridging hydrogens.

Boron Family [6]

 (f) Action of Ammonia :
3B2H6 + 6NH3    o 2B3N3H6 + 12H2
High . temp .

Borazole.

(i) Borazole has been called as inorganic benzene because it is very close to benzene in structure
and properties.
(ii) When compared with Benzene Borazol is less stable & more reactive due to palanity of N & H
in compound.
x Structure of Diborane :
B = 1s2 2s2 2p1
1s2 2s1 2px1 2py1 2pz
————————————————
sp3 Hybridisation

4 {sp3 – s} 2{ sp3 – s – sp3}

(a) 4 Terminal H–are bonded by V bond & remaining 2H are bridging hydrogens and of these are broken
then dimer become monomer.
(b) Boron undergoes sp3 hybridisation 3 of its sp3 hybridised orbitals contain one e¯ each & fourth sp3
hybrid orbital is vacant
(c) 3 of these sp3 hybrid orbitals get overlapped by s orbitals of 3 hydrogen atoms.
(d) One of the sp3 hybrid orbitals which have been overlapped by s orbital of hydrogen gets overlapped by
vacant sp3 hybrid orbital. of 2nd Boron atom. and its vice versa.
(e) By this two types of overlapping take place 4(sp3 – s) overlap bonds & 2 (sp2 – s – sp3) overlap bonds.

(f)

H is held in this bond by forces of attraction from B & This bond is called 3 centred two electron bonds.
also called Banana bonds. Due to repulsion between the two hydrogen nuclei, the delocalised orbitals of
bridges are bent away from each other on the middle giving the shape of banana.

Boron Family [7]

x Uses of Diborane :
(i) Diborane is used for preparing substances such as high energy fuel & propellents.
(ii) Boron hydrides have been tried as rocket fuels .
(iii) It is used as a catalyst in polymerisation reaction.
(iv) It is used as a reducing agent in inorganic reaction.
(v) It is used for welding torches.
x H3BO3 (Orthoboric Acid, Boric acid or Boracic acid)
Preparation :
(1) From borax :
Na2B4O7 + H2SO4 + 5H2O o Na2SO4 + 4H3BO3
Hot & conc Conc.
(2) From colemanite :
Ca2B6O11 + 2SO2 + 11H2O o 2Ca(HSO3)2 + 6H3BO3
on cooling, Boric acid crystallises out
x Properties :
(1) It forms soft pearly - white needle like crystals.
(2) It is steam volatile.
(3) Acidic nature - It is a very weak acid and ionises mainly as a monobasic acid.
It is not a proton donor but behaves as a Lewis-acid i.e. it can accept a lone pair of electrons
from OH¯ ions.
It reacts with strong alkalies forming salts known as metaborates.
B(OH)3 + NaOH o NaBO2+ 2H2O
orthoboric acid
(4) Action of heat o
o
H3BO3 100  o HBO2 + H2
C
o
4HBO2 160 
C
o H2B4O7 + H2O
H2B4O7  Re d o 2B2O3 + H2O
Heat

Tetraboric acid Boron trioxide.
(5) Reaction with ethanol -
H3BO3 + 3C2H5OH o (C2H5)3BO3 + 3H2O
Triethyl borate (green edged flame.)

Boron Family [8]

x Uses :
(1) As a antiseptic, as eye wash (eye-lotion) and as food preservatives.
(2) In leather - industry
(3) In the preparation of glass and enamels.
x Structure :
In H3BO3 (boron is sp2 hybridised), the planar triangular ortho-boric acid units, are bonded through
hydrogen bonds into two dimensional sheets.

x Al2O3(Alumina, Aluminium oxide or Corundum)

Preparation :
(a) 4Al + 3O2 o 2Al2O3
(b) 2Al(OH)3 '
o Al2O3 + 3H2O
(c) 2Al(NO3)3 o Al2O3+ 3NO2+ 9/2 O2
Strong
(d) 2 AlF3 + B2O3 Heating
 o Al O + 2BF
2 3 3
Crystalline
Properties :
(1) It is very stable and unreactive
(2) Melting point o 2050°C
Boiling point o 2980°C
(3) It is amphoteric oxide :
Al2O3 + 6HCl o 2AlCl3 + 3H2O
Al2O3 + 2NaOH o 2NaAlO2 + H2O
(4) Reaction with carbon :
2000 $ C
2Al2O3 + 9C  o Al4C3 + 6CO

4Al (OH)3 + 3CH4

Uses : (i) It is used as a refractory material.
(ii) In chromatography for separation of mixture.
(iii) In preparation of Artificial gems.
x Aluminium chloride :(AlCl3)
(a) Preparation :
Macaffc's process :
Al2O3 + 3C + 3Cl2 o 2AlCl3 + 3CO ( n)
(b) Properties :
(i) It sublimates below 200°C.
(ii) Aluminium chloride is a white crystalline substance which fumes in moist air
AlCl3 + 3H2O o Al (OH)3 + 3HCl ( n)
(iii) Its vapour density at below 350°C indicates that its formula is Al2Cl6.
The vapour density at 750° corresponds to AlCl3 as its molecular formula.
(iv) It is highly covalent therefore it is soluble in alcohol, ether and benzene.
(v) Anhy. AlCl3 forms addition compound with NH3, PH3, COCl2.
Al2Cl6 + 12 NH3 o 2[AlCl3. 6NH3]

Boron Family [9]

x FACTS ABOUT ALUMINIUM CHLORIDE (AlCl3)
* Anhy AlCl3 can be prepared by passing dry Cl2 or HCl gas over hot Al. It may also be prepared
by passing dry Cl2 gas over a hot mixture of alumina & Coke (Mac Aff’s process)
* Anhydrous AlCl3 is hygroscopic in nature & for AlCl3. 6H2O which is deliquiscent in nature.
* Anhydrous AlCl3 gives out HCl fumes when exposed to moist air (due to rapid hydrolysis).
* In organic solvents AlCl3 exists as a dimer Al2Cl6.
* In AlCl3 Al is sp2 hybridised, while in Al2Cl6 its state of hybridisation is sp3
* AlCl3 does not conduct current in the fused state.

(a) Alums : Alums are double sulphates with their general formula as M2SO4. M21(SO4)3. 24H2O
where
M = Mono valent radical like Na+, K+, NH4+ & M1 = Trivalent radicals like Al+3, Cr+3, Fe+3
etc.
(b) The different alums are :
(i) Potash alum : K2SO4. Al2 (SO4)3. 24H2O
(ii) Chrome Alum : K2SO4. Cr2 (SO4)3. 24H2O
(iii) AmmoniumAlum : (NH4)2SO4. Al2(SO4)3. 24H2O
(iv) Iron Alum : (NH4)2SO4. Fe2(SO4)3. 24H2O

Note : (i) Li does not form alum because Lithium ion too have a Co-ordination number of six.

(ii) In alums each metal ion is surrounded by six water molecules.

(iii) In univalent cation which are large in size, the six water molecule are too far from the ion while in
trivalent cations, being small in size.
Eg. [M(H2O)6]+2, [M1(H2O)6]+3
x Important Points :

(a) All Alums are isomorphous.

(b) On heating it losses its water of crystallisation and swells up.

$
200 C
Eg. K2SO4. Al2(SO4)3. 24H2O  
o K2SO4. Al2(SO4)3 + 24H2O

K2SO4. Al2(SO4)3  o K2SO4 + Al2O3 + 3SO3.

Re d Heat


(c) It is highly acidic in aq. solution due to the hydrolysis.

(d) Pseudo alums : Double sulphates of divalent ions and trivalent ions with 24 water molecules in
their crystals are known as pseudo alums.
Eg. MSO4. M21 (SO4)3. 24H2O
Where M = divalent or Bivalent
M1 = Trivalent metal
(e) Highly toxic element of Boron family is Tl.

Boron Family [10]