NEET Chemistry - p-Block Elements – Carbon Family- Study Notes

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About this unit

Carbon, allotropic forms, physical and chemical properties: uses of some important compounds: oxides.Important compounds of silicon and a few uses: silicon tetrachloride, silicones, silicates and zeolites, their uses.

p-BLOCK ELEMENTS – CARBON FAMILY

GENERAL CHARACTERISTICS

ELECTRONIC CONFIGURATION

Element	Atomic No.	Electronic configuration	Valence shell configuration
Carbon	6	[He]
Silicon	14	[Ne]
Germanium	32	[Ar]
Tin	50	[Kr]
Lead	82	[Xe]

METALLIC CHARACTER

C and Si are non metals, Ge is a metalloid and Sn and Pb are metals.

APPEARANCE

C is black , Si is light-brown, Ge greyish white, Sn and Pb are silvery white.

DENSITY

Density increases with the increase in atomic number due to increase in mass per unit volume.

MELTING POINTS AND BOILING POINTS

The melting points and boiling points decrease from carbon to lead but carbon and silicon have very high melting and boiling points due to their giant structure.

OXIDATION STATES

C	Si	Ge	Sn	Pb
(+2) <+ 4	(+2 )<+ 4	+2 <+ 4	+2<+ 4	+2> + 4

The compounds of Ge and Sn in +2 oxidation state are reducing in nature. Since their higher oxidation states +4 are more stable
The compounds of Pb in +4 oxidation state are powerful oxidising in nature. Since +2 oxidation state of Pb is more stable
The compounds in +2 oxidation state are ionic in nature and in +4 oxidation state are covalent in nature (Fajan’s rule)

NEGATIVE OXIDATION STATES

Carbon forms and in certain compounds e.g.

IONISATION ENERGY

It decreases from C to Sn . For Pb it is slightly higher than Sn.

ELECTRONEGATIVITY VALUES

The values decrease from C to Pb but not in a regular manner probably due to filling of d-orbitals in Ge and Sn and f-orbitals in Pb.

CATENATION

It is the tendency of an element to form long chains of identical atoms. The greater the strength of element-element bond, the greater is the strength of catenation.

Bond	C– C	Si–Si	Ge– Ge	Sn–Sn
Bond kJ/mole	353.3	225.7	167.2	155.0

ALLOTROPY

All the elements except Pb show allotropy.

Allotropic forms of carbon – Diamond, Graphite and Fullerene

Amorphous forms of carbon – coal, charcoal etc.

Silicon (Si) – crystalline and amorphous

Tin (Sn) – grey tin, white tin and rhombic tin

Germanium – two crystalline forms

VALENCY

All elements exhibit tetravalency. In case of Carbon 406 kJ/ mole of energy is required for promotion of 2s electron to 2p. Formation of two extra bonds provide this energy .

INERT- PAIR EFFECT

On descending the group, the stability of +4 oxidation state decreases and that of +2 oxidation state increases.

ATOMIC AND IONIC RADII

Both increase from C to Pb

ATOMIC VOLUME

Atomic volume shows a regular increase from C to Pb.

FORMATION OF COMPLEXES

C does not give any complex due to non availability of empty d orbitals in valence shell.

The valence shell of Si and other elements contain d-orbitals and can accomodate more than 8 and can therefore form complexes. e.g.,

The hybridisation in these complexes is which is octahedral.

REACTIVITY

Increases from C to Pb.

MULTIPLE BONDING

Carbon forms p

– p

multiple bonds with itself and with S, N and O. Other elements show negligible tendency of this type due to their large size. Others form d

– p

multiple bonds.

FORMATION OF COMPOUNDS

HYDRIDES

All form covalent hydrides .Their number and ease of formation decreases down the group.

Hydrides of carbon are known as Alkanes, Alkene or Alkynes.
Hydrides of Si and Ge are known Silanes and Germanes but their number is limited.
The only hydrides of Sn and Pb are SnH4 (Stannane) and PbH4 (Plumbane) .
Their thermal stability decreases down the group.
Their reducing character increases down the group.

HALIDES

All the elements give tetrahedral and covalent halides of the type

except

and

, since

is strong oxidising and

and

are strong reducing agent.SnF4 is ionic.

Stability – Order of thermal stability with common halogen

Order of thermal stability with common metals

Hydrolysis – Except other tetrahalides are hydrolysed

Ease of hydrolysis

are not hydrolysed due to absence of vacant d-orbitals in valence shell of carbon.

DIHALIDES

Except carbon other elements form dihalides of the type

which are more ionic and have higher melting points and boiling points e.g

is a solid whereas

is a liquid at room temperature.

C, Si and Ge form trihalides of the type

. Pb and Sn do not form trihalides of the type

OXIDES

They form two types of oxides

Mono-oxides of the type MO

CO forms a number of coordination compounds with transition metals e.g. Ni(CO)4, Fe(CO)5 and Cr(CO)6

Dioxides of the type MO2

Acidic – CO2, SiO2

Amphoteric – GeO2, SnO2 and PbO2

is linear, gas at ordinary temperature. Solid

is known dry ice or drikold. SiO2 is solid with three dimensional network having Si bonded to four oxygen atoms tetrahedrally and covalently.

The bond energy of

bond is 368 kJ/mol, therefore

is chemically inert and has high melting point.

and

all are network solids.

is a powerful oxidising agent

Carbon also gives suboxide

Lead also gives mixed oxide

ACIDS

All elements give acids of the type

e.g.

(carbonic acid),

(silicic acid),

(metastannic acid),

(meta plumbic acid). Carbonic acid forms two series of salts, bicarbonates

and carbonates

SILICATES

Silicates are metal derivatives of silicic acid

and can be obtained by fusing metal oxides or metal carbonates with sand e.g.

TYPE OF SILICATES

Silicates contain tetrahedral formed by

hybridisation, depending upon the number of O-atoms shared between tetrahedra and fashion, Silicates have been classified into following groups

Orthosilicates – They contain discrete tetrahedra, Examples are phenacite , willimite forsterite .
Pyrosilicates – Here two tetrahedra units are
joined by one oxygen atom forming a large discrete . Examples are thortveitite , hemimorphite
Chain silicates – Here two oxygen atoms per SiO4 tetrahedra are shared giving polymeric anion chains. Discrete unit is . Examples: synthetic sodium silicate, lithium silicate , natural spodumene , jadeite , enstatite and diopside .
Double chains – Here two simple chains are held together by shared oxygen atoms. The discrete unit is . Example mineral tremolde

Double chains silicates is also called amphibole

Cyclic silicates – Here two oxygen atoms per tetrahedra are shared giving discrete unit and . Example Beryl
Sheet-silicates – Here three oxygen atoms per tetrahedra are shared giving two dimensional sheet having discrete unit . Example

Talc

Kaolin

Framework silicates – Here all four oxygen atoms of each tetrahedra are shared. Example are quartz, zeolites, tridymite and cristobalite.

SILICONES

The polymeric compounds containing units, linear cyclic or cross linked are known as silicones. They are manufactured from alkyl substituted chlorosilanes

Silicone

Silicones are chemically inert, water repellent, heat resistant, good electrical insulators. These are used as lubricants, insulators etc.

CARBIDES

Compounds of carbon with less electronegative elements e.g. Be, B, Si etc are called carbides. These are of three types.

IONIC OR SALT LIKE

The carbides of elements of group 1, 2, 13, coinage metals, Zn,Cd. Some lanthanides give ionic or salt like carbides. Prepared by heating oxide with carbon or hydrocarbon at high temperature (2350K)

They are further classified as

Acetylides contain . These liberate acetylene on hydrolysis

They have NaCl type crystal lattice.

Methanides – These react with water to give methane.

Allylides – These react with water to give allylene.

INTERSTITIAL CARBIDES

These carbides are formed by transition elements especially Cr, Mn and Fe group metals. These are very hard.

COVALENT CARBIDES

Carbides of B and Si, B4C and SiC are covalent .SiC is known as CARBORUNDUM, used as abrasive and refractory material. B4C harder than SiC and used as an abrasive.

CARBON

It is widely distributed in the free state (diamond, graphite, coal etc.) and in the combined state (oxides, carbonates hydrocarbons etc.)

ALLOTROPIC FORMS OF CARBON

The crystalline forms include

Diamond

It is beautiful crystalline form, hardest, and has three dimensional polymeric structure, hybridisation of C is

It is covalent solid, melting point 3650°C, density and bad conductor of heat and electricity.

When heated at 1800°C – 2000°C, it is converted to graphite.

Graphite

(graphite)

It is dark grey, having hexagonal plates, hybridisation of C is , good conductor of heat and electricity due to free movement of electrons. It was also known as black lead or plumbago. It is very good lubricant.

Aqua dag – suspensions of graphite in water

Oil dag – suspension of graphite in oil lubricants

Fullerene

Fullerenes are large cage like spheroidal molecules with general formula C2n
(where n≥ 30). Two important member are C60 and C70. C60 fullerene looks like a soccer ball (so called bucky ball).

AMORPHOUS FORMS OF CARBON

Coal
Coke
Charcoal or wood charcoal
Bone-black or animal charcoal
Lamp-black
Carbon-black
Gas carbon
Petroleum coke

Varieties of coal –

Peat 60% carbon
Lignite 70%C
Bituminous 78%C
Semi bituminous 83%C
Anthracite 90%C

Anthracite is purest – amorphous form, burns without smokey flame.

Coke – Coal

Coke.

It contains C = 80-90%

Uses – Reducing agent in Iron and steel industry for making water gas and graphite.

Wood charcoal – It is obtained by strongly heating wood without access to air. When heated with steam it becomes more activated.

Uses -To remove colouring matters and odoriferous gases.

Bone-black or animal charcoal – It is obtained by destructive distillation of bones in iron retort. By products are bone oil or pyridine.

Uses – As adsorbent. On burning it gives bone ash which is calcium phosphate and used in the manufacture of phosphorus and phosphonic acid.

Lamp black – It is obtained by burning vegetable oils in limited supply of air.

Uses – In the manufacture of printing ink, black paint, varnish and carbon paper.

Carbon black – It is obtained by burning natural gas in limited supply of air.

Uses – Added to rubber mixture for making automobile tyres.

Gas carbon and petroleum coke – When coal is subjected to destructive distillation carbon deposited on walls is scraped and called gas carbon. Similarly petroleum coke is deposited while distilling crude petroleum.

Uses – Both are good conductors of electricity when pressed into sticks they make good electrodes, known as gas electrodes.

Sugar charcoal – It is obtained by heating sugar in absence of air. It is purest form of carbon.

CARBON DIOXIDE CO2

PREPARATION

Lab method

Manufacture

Fermentation
From fuel gases

PHYSICAL PROPERTIES

Colourless, 1.5 times heavier than air, can be poured downwards like

.Animals die in its presence due to lack of

, it is also known as black damp.

CHEMICAL PROPERTIES

Stability – Fairly stable, decomposed at 1775K.

Incombustible and non supporter of combustion but active metals e.g. Mg, Na, K continue burning in a jar of the gas.

Acidic nature

Lime water

Reduction
Photosynthesis

USES

In household as fire extinguisher. Dry powder fire extinguisher contains

which is decomposed by heat.

Foamite extinguisher contains baking soda and aluminium sulphate and is used for oil fires.

Structure .

Linear, dipole moment is zero.

CARBON MONOXIDE CO

PREPARATION

Lab method

Manufacture

(a) Air

(b) Steam

(water gas synthesis gas or blue gas )

Other methods

Heating

with

PROPERTIES

Neutral, colourless, poisonous, burns with blue flame. Sparingly soluble in water. With haemoglobin it gives “carboxy haemoglobin” which destroys its capacity to supply oxygen to the body.

Burning – Non supporter of combustion. Burns in air with blue flame.

Reduces ammoniacal AgNO3

Reduces Fehling-solution

Reducing nature – Metal oxides are reduced to metals.

Unsaturated nature – It gives addition products.

Formation of metal carbonyls – It acts as lewis base.

USES

In metallurgy of Ni-Monds process

Manufacture of methanol, phosgene, synthetic petrol, as reducing agent.

TEST

Burns with blue flame.
Reduces iodine pentoxide to I2.

layer terms violet)

Carbogen – (mixture of

is used for artificial respiration for victims of CO poisoning.

FUEL GASES

WATER GAS (H2 + CO)

Preparation :

– 28 kcal

Uses : Burns with blue flame, calorific value 2700 kcal/m3. Industrial source of hydrogen (Bosch process). Manufacture of methyl alcohol (Patart Process) – Synthetic petrol (Fischer-Tropsch process). For making carburetted water gas.

SEMI WATER GAS

(mixture of water gas and producer gas)

Preparation :

Composition : CO = 27.0%, H 2= 10.9%

CH4 = 1.28%, CO2 = 4.50%

N2 = 56.3%

Properties and Uses : Its calorific value 160 – 180 B.T.U. per cubic foot. As fuel in steel industry and for production of power in internal combustion engine.

PRODUCER GAS

Composition : CO = 31.7%, N2 = 65.7%, CO2 = 2.5%

Properties and Uses : Poisonous, combustible but non supporter of combustion, has low calorific value. Mainly employed as fuel.

COAL GAS

Preparation : By destructive distillation of coal

Composition : H2 = 45-55% N2 = 2-12%

CH4 = 25-35%, CO2 = 0-3%

CO = 4-11%, O2 = 1-1.5%

Ethylene, acetylene, benzene etc = 2.5-5%

Uses : Used as illuminant, as fuel, to provide inert atmosphere in metallurgical processes.

NATURAL GAS

It is found along with petroleum below the surface of earth.

Composition : CH4 = 60-80%

Higher hydrocarbons = 2-14%

C2H6 = 5-9%, C3H8 = 3-18%

Uses : It is used as a fuel. Its partial combustion yields carbon black (reinforcing agent for rubber)

OIL GAS

Preparation :

Uses : It is used as fuel in laboratories in Bunsen Burners.

WOOD GAS :

Preparation :

Uses : It is used as fuel

LIQUIFIED PETROLEUM GAS (LPG)

Composition : n-Butane + Iso-butane

Uses : It is used as domestic fuel.

GOBAR GAS :

Preparation :

Uses : As domestic fuel.

British Thermal Unit (B.T.U.) – It represents the amount of heat required to raise the temperature of one pound of water through 1ºF. One B.T.U. is equal to 252 calories.

SILICON

Silicon does not occur free in nature . In abundance it is next to .

OCCURRENCE

As oxide

(Silica )in sand, quartz, flint. As silicates
of Al, Mg , K, Fe etc. Aluminium silicate is most
widely distributed as Felspar (

)and Mica

, Feldspar (

), Kaolinite

PREPARATION OF AMORPHOUS FORM

It is very common and may be obtained by heating powdered quartz or finely divided silica with Mg powder.

PREPARATION OF CRYSTALLINE FORM

By reduction of

with molten Al

By reduction of highly purified SiCl4 with hydrogen

Zone-refining

Silicon is purified by Zone-refining process because the impurities present in it are more soluble in the liquid phase than in the solid phase.

PROPERTIES

Crystalline form possesses metallic lustre. It is very hard and scratches glass. Crystalline silicon is isomorphous with diamond.

Chemical reactions of amorphous silicon: Burns in air

USES

Silicon chips used for computing devices are doped with P,As, Al or Ga to enhance the semiconductor properties.

COMPOUNDS OF SILICON

SiO2 (silica) – It exists in three crystalline forms Quartz, Tridymite and cristobalite. Further each form has and form. At low temperature the form is stable and at high temperature the form is stable .
Sand – It is crushed form of quartz produced in nature by weathering of rocks .
Flint – It is amorphous silica associated with quartz .
Kieselguhr – Siliceous rock composed of the remains of sea organisms. Used as absorbent for nitroglycerine.
Quartz or rock crystal – It is purest form of silica It is optically active.
Silicic acid

Ortho silicic acid

Metasilicic acid

Silicic acid sol – Colloidal solution of silicic acid
Silica gel – Transparent gel of bluish white colour
Water glass or sodium silicate – Sodium silicate containing excess of SiO2.

Silica garden – Aqueous solution of sodium silicate containing crystals of various coloured salts e.g. copper sulphate, cobalt nitrate , manganese chloride, nickel chloride etc.
Hydrofluorosilicic acid H2SiF6

Permutit – Artificially prepared sodium aluminium silicate containing varying composition of sodium ,aluminium and silica .
Used for softening hard water.
Zeolites -They have honeycomb like structure and have the general formula

They act as ion exchanger and molecular sieves. They can be artificially prepared by heating China clay, Silica and

Ultramarines – Zeolite type silicates, containing ions likeand not water, are known as ultramarines e.g.. Many of them are coloured and used as pigments and calico printing.
Carborundum – silicon carbide

It is nearly as hard as diamond.

GLASS

Amorphous, hard, brittle, transparent, translucent supercooled solution of various silicates and borates of K, Ca and Pb. It has no definite formula but roughly can be represented as

Raw material used in the manufacture of glass.

SiO2
Na2CO3, K2CO3 or NaNO3, KNO3
Alkaline earth metals e.g. CaCO3, BaCO3
Oxides of heavy metals
Cullets (pieces of glass)
Colouring matter

MANUFACTURE

Mixture of raw materials

till CO2 escapes

clear liquid. After some cooling it is used for casting articles

Annealing – Process of slow cooling of glass is known as annealing. The glass becomes soft.

TIN (Sn)

PRINCIPAL ORES OF TIN

Cassiterite or Tin stone, SnO2
Tin Pyrites, SnS.Cu2S.FeS.

EXTRACTION

Concentration – By gravity process washing with water and then magnetic separation.
Roasting -To remove volatile impurities

Smelting – It is carried out in reverberatory furnace with coal (powdered anthracite) and limestone.

Sn so obtained contains iron and other metals and called black tin .

Refining by (a) Liquation (b) Poling and (c) Electrolytic

PROPERTIES

Soft silvery white metal, ductile and malleable. It has maximum number of isotopes and three allotropic forms.

Grey⇌ 18℃ White ⇌161℃ Rhombic

Tin cry – It produces a peculiar cracking sound on bending which is known as tin cry.

Tin plague – It is the conversion of white tin to grey tin at low temperature which crumbles into powder.

Tinning – Since tin is not attacked by organic acids the utensils are protected by thin layer of tin .A pinch of

is sprinkled over hot and clean surface, when HCl liberated removes the oxide film.Tin then rubbed over the clean surface with the help of rag dipped in

powder. The utensil is immediately dipped in water to avoid oxide formation .

Tin plating – It involves the deposition of thin protective layer of tin over sheets of iron electrolytically.

CHEMICAL PROPERTIES

With acids

Metastannic acid

COMPOUNDS OF TIN

STANNIC OXIDE (SnO2)

It occurs naturally as cassiterite.

PREPARATION

PROPERTIES

White solid, insoluble in water and amphoteric in nature.

USES

As polishing powder, in glass and pottery manufacture.

STANNOUS OXIDE (SnO)

PREPARATION

PROPERTIES

It is black solid and amphoteric in nature.

SULPHIDES

SnS precipitated by

.It is dark brown solid, soluble in yellow ammonium sulphide forming

STANNOUS CHLORIDES ()

PREPARATION

Anhydrous

PROPERTIES

White crystalline solid, soluble in water, alcohol and ether.
Hydrolysed in water

Strong reducing agent

BUTTER OF TIN

used as mordant in dyeing.

PURPLE OF CASSIUS

Colloidal particles of gold absorbed by stannic acid Sn

is known as purple of cassius. It is used for colouring glass and pottery.

ALLOYS OF TIN

Some important alloys of tin are

Solder Sn 50-70% Pb 30-50%
White metal Sn 82% Sb 12% Cu 6%
Britannia metal Sn 90% Sb 7% Cu 3%
Soluminium Sn 55% Zn 33% Al 11% Cu 1%
Babbitt metal Sn 90% Sb 7% Cu 2%
Pewter Sn 80% Pb 20%
Dental alloy Alloy of Sn, Ag, and Hg

LEAD

PRINCIPAL ORES

Galena PbS
Anglesite PbSO4
Cerussite PbCO3

EXTRACTION

From galena – Two important processes are:-

Air reduction process

(i) Concentration – By froth floatation process

(ii) Roasting – Roasted in air at 500°C – 600°C.

Carbon reduction process

Mixed sulphides (PbS & ZnS) are roasted to obtain oxides which are fed into blast furnace with coke and lime.

Molten lead tapped off from the bottom.

PURIFICATION

Electrolytic method to remove Cu, Ag, Au, Sb etc.

PROPERTIES

Bluish, grey lustrous metal which acquires dull appearance when exposed to air due to formation of basic carbonate (Pb(OH)2.PbCO)3. Poor conductor of electricity.