Si

Carbon and Silicon

Group IV A (14)2s2 2p2

3s2 3p2

3d10 4s2 4p2

4d10 5s2 5p2

5d10 6s2 6p2

Group IV AProperty C Si Ge Sn Pb

Density (g/cm3) 3.51, 2.22 2.33 5.36 7.31 11.13

I. Potential (eV) 11.2 8.1 7.8 7.3 7.4

m.p 3570 1414 959 232 328

b.p 4827 2355 2830 2362 1755

At. Radium (nm) 0.077 0.117 0.122 0.141 0.154

E.N. 2.5 1.8 1.7 1.7 1.7

Properties

• At. radius, volume and density increase down the group

• m.p. and b.p. generally decrease. Inter atomic forces.

• Metallic character increases with increase in atomic number

• I.E. (C to Sn decreases, Pb higher, due to screening of d orbital)

• EN • Allotropy – all elements except Pb

• Oxidation states C , Si +4, Ge, Sn, Pb +2, +4, inert pair effect increases down the group, so M (+4) stability decreases

• Catenation decreases down the group. Due to decreases in energy of M-M bond C-C 348, Si-Si 222, Ge-Ge 167, Sn-Sn 155, Pb-Pb 0

Carbon and Silicon

Similarities• In nature• Tetravalent• Allotropy• Oxygen –burn • Covalent hydrides• Similar halides

Differences• 2 e, 8 e in penultimate shell• Black solid , reddish brown

solid• Catenation strong, weak• No effect of alkali, aqueous

and fused alkali H2

• Covalency 4, 6• CCl4 stable, SiCl4 less stable

Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, known as allotropes of these elements. Allotropes are different structural modifications of an element; the atoms of the element are bonded together in a different manner.

CarbonElemental carbon exists in nature mainly as the two allotropes diamond and graphite

Graphite is used in writing material in pencils, electrodes, high-temperature devices, and strong graphite fibers

Carbon also exists in amorphous forms, such as charcoal

Diamond is used in jewelry, abrasives, and in drill bits because it is the hardest substance known and has a high thermal conductivity

Green-house effectThe greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere. As a result, the average surface temperature is higher than it would be if direct heating by solar radiation were the only warming mechanism

Silicon

• 2nd most abundant element, found with Oxygen

• 27.6% by weight of Earth Crust• SiO2 – quartz, flintz, agate and sand

• Silicon – hard, brittle, solid• Diamond like structure

Silicones

• RSiCl3, R2SiCl2 hydrolize to give silicols• Condensation of silicols with elimination of

water gives silicones

Silicones

Oils, viscous fluids, resins, rubber like solids• Silicon-oil highly stable, non volatile. Vacuum pumps• Not too viscous on cooling – low T lubrication• Vaseline like greases – aeroplanes -40 – 200 C• Water-repellents – water proof paper• Insulating materials

Silicates

• Metal derivatives of silicic acid• Meta- (H2SiO3) ortho- (H4SiO4) and pyro-silicic

acid (H6Si2O7)• Fusing metal oxide or carbonate with sand

Na2CO3 + SiO2 Na2SiO4, (Na2SiO3)n etc

• Some silicates of Alkali metals are soluble in water. Na, K silicates are soluble glass

Silicates

• XRD – silicates have SiO44- anions – sp3

hybridization, tetrahedral geometry• Orthosilicates• Pyrosilicates• Ring or cyclic silicates• Metasilicates of chain silicates• Sheet silicates• Three dimensional silicates