General Physical Properties of Group 14 Elements
(i) Electronic configuration Their valence shell electronic configuration is ns2 np2.
[He] 2s2 2p2
[Ar] 3d10, 4s2 4p2
[Kr] 4d10, 5s2 5p2
[Xe] 4f14, 5d10,6s2 6p2
(ii) Metallic character C and Si are non-metals, Ge is a metalloid and Sn and Pb are metals.
(iii) Appearance C is black. Si is light-brown, Ge is greyish, Sn and Pb are silvery white.
(iv) Density Density increases with increase in atomic number due to increase in mass per unit volume down the group.
(v) 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.
(vi) Oxidation state: They exhibit +2 and +4 oxidation state. The compounds of Pb in +4 oxidation state are powerful oxidizing agents since, +2 oxidation state of Pb is more stable due to inert pair effect.
The compounds in +2 oxidation state are ionic in nature and in + 4 oxidation state are covalent in nature (According to Fajan’s rule).
(vii) Ionisation enthalpy: It decreases from C to Sn. For Pb, it is slightly higher than Sn.
(viii) Electronegativity values: The value decreases from C to Pb but not in a regular manner probably due to filling of d-orbitals III and Sn and f- orbitals in Pb.
(ix) Catenation: The greater the strength of the element-element bond, the greater is the strength of catenation.
C >> Si > Ge = Sn > Pb (catenation).
(x) Allotropy: All the elements of this group except Pb exhibit allotropy.
In cold countries, white tin changes to grey tin and results in decrease in density. This is called tin disease or tin plague.
(xi) Valency: All elements exhibit tetra valency. In case of carbon, 406 kJ mol-1 of energy is required for promotion of 2s – electron to 2p.
Formation of two extra bonds provide this energy.
(xii) Atomic and ionic radii: Both increase from C to Pb.
(xiii) Multiple bonding Carbon forms pπ – pπ bonds with itself and with S, N and O. Other elements show negligible tendency of this type due to their large size. Others form dπ – pπ multiple bonds.
Chemical Properties of Group 14 Elements:
(a) Hydrides: All members of the group form covalent hydrides. Their number and ease of formation decreases down the group.
Hydrides of carbon are called hydrocarbons (alkanes, alkenes or alkynes).
Hydrides of Si and Ge are known as silanes and germanes.
The only hydrides of Sn and Pb are SnH4 (stannane) and PbH4 (plumbane),
Their thermal stability decrease down the group.
Their reducing character increases down the group.
(ii) Halides- All the elements give tetrahedral and covalent halides of the type MX4 except PbBr4, and PbI4.
CX4 > SiX4 > GeX4 > SnX4 > PbX4
Order of thermal stability with common metals:
MF4 > MCl4 > MBr4 > MI4
Except CX4 other tetrahalides can be hydrolysed due to the presence of vacant d-orbitals.
SiX4 + 2H2O → SiO2 + 4HX.
Ease of hydrolysis: SiX4 > GeX4 > SnX4 > PbX4
Except C, other elements form dihalides of the type MX2 which are all ionic and have higher melting points and boiling points, e.g., SnCl2 is a solid whereas SnCl4 is a liquid at room temperature.
SnCl2 . 5H2O is called bitter of tin and is used as a mordant in dyeing.
(iii)Oxides: They form two types of oxides. mono-oxides of the type MO. e.g.,
CO (neutral) and SiO, GeO, SnO, PbO(all basic) and dioxides of the type MO2.
CO2 is linear gas at ordinary temperature. Solid CO2 is known as dry ice or drikold.
SiO2 is a solid with three dimensional network in which Si is bonded to four oxygen atoms tetrahedrally and covalently. A mass of hydrated silica (SiO2) formed from skeletons of minute plants, known as diatoms, is called kieselguhr. It is a highly porous material and is used in the manufacture of dynamite.
Free states (diamond. graphite, coal etc.) and combined states (oxides, carbonates, hydrocarbons etc.)
Allotropic Forms of Carbon:
The crystalline forms include-
(i) Diamond It is the hardest and has three dimensional polymeric structure in which hybridization of C is sp3. It is covalent solid. melting point 3650°C. density 3.51 g/cm3 and bad conductor of heat and electricity.
(ii) Graphite It is dark grey having hexagonal plates, hybridization of each C is sp2. It is good conductor of heat and electricity due to the presence of free electrons. It was also known as black lead. It is a very good lubricant.
Aqua dag Suspensions of graphite in water.
Oil dag Suspension of graphite in oil lubricants.
(iii) Fullerenes These are the only pure form of carbon. C60 molecule contains 12 five membered rings and 20 six membered rings. The five membered rings are connected to six membered rings while six membered rings are connected to both five and six membered rings. These are used in microscopic ball bearings, light weight batteries, in synthesis of new plastics and new drugs.
Amorphous forms of carbon are:
(i) Coal The different forms of coal are peat (60 % C), lignite (70 % C), Bituminous (78 % C), Semi Bituminous (83 % C) and anthracite (90 % C). Bituminous is most common variety of coal.
(ii) Coke is obtained by destructive distillation of coal.
(iii) Charcoal or wood charcoal: It is obtained by heating wood strongly in absence of air. When heated with steam, it becomes more activated. It is used to remove colouring matters and odoriferous gases.
(iv) Bone black or animal charcoal It is obtained by destructive distillation of bones in iron retort. By products are bone oil or pyridine. It is used as adsorbent. On burning, it gives bone ash which is calcium phosphate and used in the manufacture of phosphorous and phosphoric acid.
(v) Lamp-black It is obtained by burning vegetable oils in limited supply of air. It is used in the manufacture of printing ink, black paint, varnish and carbon paper.
(vi) Carbon-black It is obtained by burning natural gas in limited supply of air. It is added to rubber mixture for making automobile tyres.
Preparation- By destructive distillation of coal.
H2 = 45 – 55 % N2 = 2 – 12 %
CH4 = 25 – 35 % CO2 = 0 – 3 %
CO = 4 – 11 % O2 = 1 – 1.5 %
Ethylene, acetylene, benzene, etc. = 3 – 5 %
Uses It is used as illuminant, as fuel and to provide inert atmosphere in the metallurgical processes.
It is found along with petroleum below the surface of earth.
Composition CH4 = 60 – 80 %
Higher hydrocarbons = 2 – 12%
C2H6 = 5 – 10 %, C3H8 = 3 – 18 %
Uses It is used as a fuel. Its partial combustion yields carbon black (reinforcing agent for rubber).
Uses: It is used as fuel in laboratories in Bunsen burners.
Preparation: Destructive distillation of wood gives wood gas (CH4, C2H6 H2)
Uses: It is used as fuel.
Liquified Petroleum Gas (LPG)
Composition n-butane + Iso-butane
Uses It is used as domestic fuel.
Carbon Monoxide (CO)
(iii) It is manufactured in the form of water and produces gas.
It is colourless, odourless and almost water insoluble gas. It is a powerful reducing agent. CO is used in the extraction of many metals from their oxide ores.
Carbon Dioxide (CO2):
Properties: It is a colourless and odourless gas. With water, it forms carbonic acid.
Compounds of Silicon
Silicates are metal derivatives of silicic acid, H2SiO3 and can be obtained by fusing metal oxides or metal carbonates with sand. The basic structural unit of silicates is SiO44-.
Types of silicates
No. of oxygen atom shared
(SiO32-)n and (Si40116-)
Pyroxenes Kaoiinite, talc. (3MgO.4Si02H2O)
Three dimensional silicates
quartz, tridymite, cristobalite.
Talc consists of planar sheets which can slip over one another due to weak forces of attraction, and is a constituent of talcum powder. That’s Why talcum powder has a slippery touch.
Mica (abrak) is naturally occurring aluminium silicate [KH2AI3(SiO4]3 or KAI3Si3O10(OH)2.
The linear, cyclic or cross linked polymeric compounds containing (R2SiO) as a repeating unit, are known as silicones. They are manufactured from alkyl substituted chlorosilanes.
Silicones are chemically inert, water repellent, heat resistant, good electrical insulators. These are used as lubricants (vaseline), insulators etc.
It is second hardest material known and has formula SiC (silicon carbide). It is used as high temperature semiconductor, in transistor diode rectifiers.
It is a transparent or translucent amorphous substance obtained by fusion of sodium carbonate (or sodium sulphate), calcium carbonate and sand (silica). It is not a true solid, so its melting point is not sharp.
General formula of glass is Na2O * CaO * 6SiO2.
Coloured glasses are obtained by adding certain substance to the molten mass.
Fe2+ and Cr
Fe3+ uranate of sodium
CiO, selenium oxide
Organic matter and C
Different Varieties of Glass:
Resistant to acid and chemicals
High refractive index so used in optical lenses and prisms
T Rex glass
Mixture of borosilicate of Pb, Ca and Na
Low coefficient of thermal expansion so can with stand sudden changes in temperature
Contains CeO2 along with general composition
Absorbs UV radiations so used In making goggles
Contains mixture of Zn and Ba borosilicates
Resistant to heat, shock, etc,
Optical instruments (vitreous)
Glass is attacked by HF. This property is used in the etching of glass.
Compounds of Lead:
Chrome yellow (PbCrO 4 )
It is prepared by adding potassium chromate to lead chromate and is used as a yellow pigment under the name chrome yellow. On treating with alkali. It gives basic lead chromate or chrome red, PbCrO4 * PbO.
Basic lead carbonate, Pb(OH)2 . 2PbCO3
It is also known as white lead and is prepared by adding sodium carbonate solution to any lead salt.
3Pb(NO3)2 + 3Na2CO3 + H2O → Pb(OH)2 * 2PbCO3 + 6NaNO3 + CO2
It is used as white paint. The disadvantage of using white lead in paints is that it turns black by the action of H2S of the atmosphere.
Lead poisoning is called plumbosolvency which increases in the excess of nitrates, organic acids and ammonium salts.