dokumen.tips_51-p-block-elements-2.ppt..

Super

1. Chemistry

2. Session Objectives
1.Chemical properties of group 14 elements
2.Extraction and properties of silicon
3.Extraction of tin
4.Extraction of lead
5.Silicates and silicones
6.Glass
7.General properties of group 14 elements
8.Oxoacids of phosphorous

3. Action of Acids on group 14 elements
Non-oxidising acids do not attack carbon and silicon. Ge is
not attacked by dilute HCl. However, when metal is heated in
a stream of HCl gas, germanium chloroform is formed.32
Ge 3HCl GeHCl H   22
Sn 2HCl SnCl H   22
Pb 2HCl PbCl H   2 2 4
(chloroplumbous acid)
PbCl 2HCl H PbCl
Lead dissolves in Conc. HCl formig chloro-plumbous acid.
Tin dissolves slowly in dilute HCl but readily in Conc. HCl.

4. Action of Alkalies
Carbon is unaffected by alkalies. Silicon reacts slowly
with cold aq. NaOH and readily with hot solution to
form silicate.2 2 3 2
Si 2NaOH H O Na SiO 2H   
Sn and Pb are slowly attacked by cold alkali but
readily by hot alkali giving stannates and plumbates.2 2 3 2
Sn 2NaOH H O Na SnO 2H    2 2 3 2
Pb 2NaOH H O Na PbO 2H   

5. Oxides of group 14 elements
Carbon forms the oxides CO, CO
2, C
3O
2,
Si forms SiO
2, which is solid at room temperature because it exists in the
form of a three-dimensional network due to lack of formation of pbonds
with oxygen. Three crystalline modifications of SiO
2are quartz,
cristobalite and tridymite
Pb forms a number of oxides like PbO, PbO
2, Pb
2O
3, Pb
3O
4(red lead).
Pb
3O
4is actually 2PbO.PbO
2
GeO
2, SnO
2etc are also network solids. SnO
2 is used as a polishing
powder and also in the manufacture of glass and pottery
2Pb(NO
3)
2 -2PbO + 4NO
2+ O
2
6PbO + O
22Pb
3O
4
Pb
3O
4+ 4HNO
3 Pb(NO
3)
2 + PbO
2+ 2H
2O

6. Halides of group 14 elements
React with halogens directly to form tetrahedral
and covalent halides except C.
CCl
4 does not undergo hydrolysis due to non availability of d orbital.
SiCl
4and the halides of heavier metals can undergo hydrolysis due to
availability of vacant d orbitals.
SiCl
4on hydrolysis gives silicic acid (H
4SiO
4).
Apart from tetrahalides, germanium, tin and lead form
dihalides MX
2. The stability of the dihalides increases
steadily in the sequence CX
2 < SiX
2 < GeX
2 < SnX
2 < PbX
2
PbBr
4and is PbI
4do not exist because is a
strong oxidant and Br
-
and I
-
are strong reductants.4
Pb


7. Illustrative Example
Explain why PbCl
4is less stable than SnCl
4?
In the 14
th
group, the stability of +4 oxidation state decreases
down the group so Pb
4+
is less stable than Sn
4+.
This is actually due
to the inert pair effect as s-electrons do not participate in bond
formation.
Solution

8. Extraction and properties of Si
By reduction of sand SiO
2with coke in an electric furnace(96-98% pure).22273 2773 K
2
SiO 2C Si 2CO

  
Semiconductor grade silicon is prepared mainly by the
reduction of SiCl
4/SiHCl
3 with H
2or by the pyrolysis of SiH
4
At room temperature Si is unreactive towards all elements except flourine.
Combines with halogens, N
2and O
2at high temperature.
Forms carborundum(SiC) with carbon; extremely hard; used as
abrasive and refractory material.
With hot aqueous alkali liberates hydrogen.4
42
Si 4OH (aq) SiO (aq) 2H

  

9. Extraction of tin
Tin is commonly available as the mineral cassiterite, SnO
2.
SnO
2+ 2C Sn + 2CO
The roasted ore is heated with coal in a reverberatory furnace at 1500 K.
Ore is crushed and washed with water to remove
impurities such as arsenic and sulphur as volatile
oxides.
Tin is remelted on inclined surface to remove the
impurities having higher melting point.

10. Properties of tin
Tin is a soft, silvery white metal. It is ductile and can
be rolled into thin foils.
Tin is not attacked by air or water at ordinary temperatures:
Heating with air or oxygen results in the formation of SnO
2.
Tin is used as a coating on metals and in making various
alloys like solder, bronze. It is also used for electroplating
steel to make tin-plate. Tin –plate is extensively used for
making cans for food and drinks.

11. Lead
Lead is mostly used in storage batteries, in alloy
making and pigments/chemicals. PbCrO
4is used as
a strong yellow pigment for road signs and
markings. Lead compounds are also included in
crown glass and cut glass, and in ceramic glazes.
The ore is concentrated by froth-floatation and then roasted in a
limited supply of air to give PbO which is reduced to the metal by
heating with coke and limestone in a blast furnace.
The molten lead is tapped from the bottom of the furnace.
(i) 2PbS + 3O
2 2PbO + 2SO
2
(ii) PbO + C
Pb + CO
(iii)PbO + CO
Pb + CO
2
(iv) PbS + 2PbO3Pb + SO
2

12. Toxicity of Lead
Pb
3(OH)
2(CO
3)
2
Large amounts of lead in a child's blood can cause brain
damage, mental retardation, behavior problems, anemia, liver
and kidney damage, hearing loss, hyperactivity, developmental
delays, other physical and mental problems, and in extreme
cases, death.

13. O
O
–
O
–
–
O
–
O Silicates
Orthosilicates :contain single discrete unit of
SiO
4
4–
tetrahedra
Pyrosilicates
Basic unit is (Si
2
O
7
)
-6

14. Cyclic structure
Basic unit is (Si
6
O
18
)
-12
Example is beryl, Be
3Al
2Si
6O
18

15. Linear silicate chain
Continuous single chain units of tetrahedra each
sharing 2 oxygens.Basic unit is(SiO
3
)
-2
or (Si
2
O
6
)
-4
.
e.g., pyroxenes; MgCaSi
2O
6.

16. Amphiboles
Continuous double chain units of tetrahedra
each sharing 2 and 3 oxygens alternately.
Basic unit is (Si
4
O
11
)
-6
or (Si
8
O
22
)
-12
e.g., asbestos; [Mg
3(Si
2O
5)(OH)
4]

17. Phyllosilicates
Continuous sheet units of tetrahedra each sharing 3 oxygens
Basic unit (Si
2
O
5
)
-2
e.g.Mica

18. 3 D framework
Continuous framework of tetrahedra each sharing
all 4 oxygen atoms.
Basic units can be (SiO
2
) e.g. zeolites,feldspar

19. Silanes and Silicones
The hydrides of silicon are called silanes having
general formula Si
nH
2n+2
Polymeric organo-silicon compounds containing Si-O-Si bonds
are called silicones. These have the general formula (R
2SiO)
n.
Where R is CH
3group (majority cases) or C
6H
5group.

20. Focus On Glassmaking
Small amounts of impurities impart
beautiful colours.
•Fe
2O
3green
•CoO blue
Glass is a mixture of sodium and calcium silicates.
Lead-potash glass has high refractive index and
used in lenses.
Adding B
2O
3 gives, borosilicate glass (Pyrex)
having low coefficient of thermal expansion and
used in making laboratory glasswares.
Soda lime glass or Soft glass.o
1300 C
2 3 2 2 3 3 2 2
CaO Na CO 6SiO Na CO .CaSiO .4SiO CO   
Glass is not a true solid and don’t have definite melting point.

21. Group 15 elements
Nitrogen N [He] 2s
2
p
3
Phosphorus P [Ne] 3s
2
3p
3
Arsenic As [Ar]3d
10
4s
2
4p
3
Antimony Sb [Kr]4d
10
5s
2
5p
3
Bismuth Bi [Xe]4f
14
5d
10
6s
2
6p
3

22. General trends of group 15 elements
The covalent radius increases down the group.
All elements have nearly same and low
electronegativity except nitrogen.
P, As, Sb and Bi are solids under normal conditions.
The value of ionization energy is quite high for the members of
group 15 than the corresponding members of group 14. This is
due to smaller atomic radii, increased nuclear charge and
stable electronic configuration of half filled orbitals.
Ionisation energy

23. Illustrative Problem
Why nitrogen exists as N
2whereas
phosphorous exists as P
4
Because d orbitals are not available in nitrogen.
Solution :

24. Oxidation state
Stability of +3 oxidation state increases down the
group while that of +5 oxidation state decreases
down the group.
Bi
5+
salts are very rare and good oxidising agents
As
3+
salts are good reducing agents.

25. Oxidation Number Nitrogen Compound Phosphorus Compound
0 N
2
P
4
+3 HNO
2
(nitrous acid) H
3
PO
3
(phosphorous acid)
+3 N
2
O
3
P
4
O
6
+5 HNO
3
(nitric acid) H
3
PO
4
(phosphoric acid)
+5 NaNO
3
(sodium nitrate)Na
3
PO
4
(sodium phosphate)
+5 N
2
O
5
P
4
O
10

26. Down the group, covalent character,
basicity and thermal stability
decrease while reducing character increases.
NH
3 > PH
3 > AsH
3 > SbH
3> BiH
3
107°48’ 93°48’ 91°48’ 91°18’ 90°
Hydrides: MH
3

27. Illustrative Problem
Explain why NH
3is a stronger base than PH
3?
Solution
Since phosphorus is bigger in size as compared to nitrogen so,
availabilty of lone pair is less. Thus PH
3is a weaker base than NH
3

28. Illustrative Problem
Give the order of basicity and reducing character
and stability for the following hydrides: NH
3, PH
3,
AsH
3, SbH
3
Solution :
Basicity NH
3 > PH
3> AsH
3> SbH
3
Stability NH
3 > PH
3> AsH
3> SbH
3
Reducing character NH
3 < PH
3< AsH
3< SbH
3

29. Oxides of nitrogen

30. Oxides of nitrogen

31. Illustrative Problem
Which oxide of nitrogen is coloured ?
NO
2has unpaired electrons,so it is coloured.
Solution :

32. Oxides
Oxides of phosphorous
—P
4O
6and P
4O
10
P, As, Sb and Bi form two types of oxides: M
2O
3and M
2O
5and exists
as dimer due to reluctance for bonding.ppp p
Both P
4O
6and P
4O
10are acidic oxides which dissolve in water to give
phosphonic acid and phosphoric acid respectively.

33. Halides
Forms two series of halides;
MX
3 (pyramidal)
MX
5(trigonal bipyramidal)
Trihalides readily hydrolyse with water.3 2 4
NCl 4H O NH OH HOCl   3 2 3 3
PCl 3H O H PO 3HCl   3 2 3 3
AsCl 3H O H AsO 3HCl   32
SbCl H O SbO 3Cl 2H
  
    32
BiCl H O BiO 3Cl 2H
  
   
PCl
5is molecular in gas and liquid phases but exists
as [PCl
4]
+
[PCl
6]
-
in the solid state .

34. Illustrative Example
Explain why PCl
5exists but NCl
5does not?
Solution
NCl
5is not formed because nitrogen does
not have d-orbitals.

35. Illustrative Example
Solid phosphorous-pentachloride exhibits some
ionic character, why?
Solution
This is because PCl
5exists as [PCl
4]
+
[PCl
6]
-
in solid
phase and hence exhibits ionic character.

36. Allotropy of P
White phosphorus:
Waxy solid, insoluble in water, highly soluble in CS
2and benzene,
highly reactive, highly toxic and glow in dark.
Stored in water because ignite spontaneously in air.
Consist of discreate molecules P
4.

37. Allotropy of P
Black phosohorus :
Inert and has layered structure.470 K,high pr.
Whitephosphorus Blackphosphorus
Most stable form
Red phosphorus:570 K
Whitephosphorus redphosphorus
Amorphous and polymeric structure.
Less reactive and nontoxic

38. Oxy-acids of PP P
O O
O
P
O
OH
OHO
O
OH
(HPO ) Cyclic phosphoric acid
33
P
H
OHH
O
HPO Hypophosphorus acid
2
P
OH
OHHO
O
H PO
Ortho phosphoric acid
34
P
OH
OHO
O
P
OH
OH
O
Di phosphoric acid
H P O
4 2 7
P
OH
OHH
O
H PO
Phosphoric acid
33

39. Phosphatic fertilizers
Fertilizers usually contains N,P,K. Generally the ratio of N-P-K is written as
10-10-10 which indicates the percentage of N, P
20
5, and K
2O .
Most important phosphatic fertilizer is the
superphosphate of lime, Ca(H
2PO
4)
2 which is produced
from the treatment of phosphatic rock with sulphuric
acid.3 4 2 2 4 2 4 2 4
Ca (PO ) 2H SO Ca(H PO ) 2CaSO  
Triple superphosphate Ca(H
2PO
4)
2.H
2O 5 4 3 3 4 2 2 4 2 2
Ca (PO ) F 7H PO 5H O 5Ca(H PO ) .H O HF   

40. Eutrophication
Eutrophicationis the enrichment of an ecosystemwith
chemical nutrients, typically compounds containing nitrogen
orphosphorus.

41. Thank you