CARBON AND ITS COMPOUNDS

CARBON IS A NON-METAL

SYMBOL :C ATOMIC No : 6 VALENCY : 4 Group No: 14 It occurs in elemental form as well as in combined form such as CARBONATES, COAL, PETROLEUM AND CO2

The compounds of carbon are called ORGANIC COMPOUNDS.

Carbon is one of the least abundant elements in the Earth's crust, but the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen.

It is present in all known lifeforms, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen

This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.

Allotropy & Allotropes

Allotropes are different physical forms of the same element which have same chemical properties but different physical properties, and the phenomenon is known as Allotropy.

Carbon exhibit allotropy. The three relatively well-known allotropes of

carbon are amorphous carbon, (charcoal, lampblack (soot) and activated carbon ) graphite, and diamond.

Allotropes of carbon There are several allotropes of carbon of which the best known

are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic

form. For example, diamond is highly transparent, while graphite is opaque and black.

Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper (hence its name, from the Greek word "to write").

Diamond has a very low electrical conductivity, while graphite is a very good conductor.

Under normal conditions, diamond has the highest thermal conductivity of all known materials.

All the allotropic forms are solids under normal conditions but graphite is the most thermodynamically stable.

Clear (diamond), black (graphite)

Appearance

Graphite ore Raw diamond crystal

Structure of Diamond and Graphite

Allotropes of Carbon - Fullerenes In 1985 the carbon structure family

was completed by a new modification of pure carbon. With the discovery of the fullerenes by Curl, Smalley and Kroto [1] and additionally with the possibility for the production of fullerenes in large amounts shown by Krätschmer and Huffman [2] in 1990 the scientific competition in experimental and theoretical research was started.

BONDING IN CARBON COMPOUNDS THE COVELENT BOND

A bond formed between two atoms by mutual sharing of electrons between them so as to complete their octet is known as covalent bond.

A carbon atom has 4 electrons in its valence shell, so it needs 4 electrons to attain stable electronic configuration of nearest noble gas.So carbon forms bond by sharing its valence electron with any other atom.

C

Formation of methane molecule

C HC H H

H

H

+ 4--

Structure of Methane CH4

Tetravalent Nature Due to its tetravalent nature carbon always form

covalent bonds by sharing electrons with one, two, three or four carbon atoms or atoms of other elements or groups of atoms as discussed earlier.

The tetra covalency of carbon atom allows it to combine easily with other carbon atoms to form a stable chain like structure i.e., exhibiting the property of catenation. Catenation usually occurs because the atom-to-atom covalent bond is quite strong. The chains having different chain lengths and structures and combines with different elements it leads to the formation of a large number of compounds

) Molecular CompoundsThe simplest molecule is H2:

The pair of shared electrons constitutes a covalent bond.

Increased electron densitydraws nuclei together

Lewis Structures• Covalent bonding in a molecule is repre-

sented by a Lewis structure.

• A valid Lewis structure should have an octet for each atom except hydrogen.

H H+

Cl Cl

H2: or H H

Cl2: Cl

Cl

+

or Cl Cl

H H

Bondingelectrons

Nonbonding electrons

Lewis StructuresDraw Lewis structures for:

HF:

H2O:

NH3:

CH4:

H F

or H F

H O H

or H O H

H N HH

or H N H

H

H C HH

H

or H C H

H

H

Double and Triple Bonds• Atoms can share four electrons to form a

double bond or six electrons to form a triple bond.

• The number of electron pairs is thebond order.

O2:

N2:

=O O

N N

Unique properties of Carbon atom Carbon has the ability to form very long chains of

interconnecting C-C bonds. This property is called catenation.

Carbon-carbon bonds are strong, and stable. This property allows carbon to form an almost infinite number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined except those of hydrogen (because almost all organic compounds contain hydrogen too).

The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms.

Formation of covalent bond in carbon compounds Formation of Strong C-C Covalent Bonds The single bond formed between the carbon atoms

is strong. This results in the formation of stable compounds. Carbon atom can also form stable bonds with other atoms like H, Cl, Br, O, etc.

Formation of C-C Multiple Bonds Due to its small size the carbon atom can also form

multiple bonds i.e., double and triple bonds with not only carbon but with atoms of other elements like oxygen, nitrogen, etc. The formation of these multiple bonds gives rise to a variety in the carbon compounds.

Formation of C-C Multiple Bonds

Types and number of bonds

Structure

Linked to four atoms with four single bonds. Tetrahedral geometry (sp3

hybridisation)

Linked to three atoms with two single and one double bond. Trigonal geometry (sp2

hybridisation)

Linked to two atoms with one single and one triple bond. Linear geometry (sp hybridisation)

Types and number of bonds Structure

Linked to four atoms with four single bonds. Tetrahedral

geometry (sp3 hybridisation)

Linked to three atoms with two single and one double bond.

Trigonal geometry (sp2 hybridisation)

Linked to two atoms with one single and one triple bond.

Linear geometry (sp hybridisation)

Homologous series All organic compounds are made up of a

progressively building chain of carbon atoms with a number of compounds having the same functional groups.

Such a series of similarly constituted compounds are called a homologous series.

Members of a homologous group are similar in structure and display similar chemical characteristics.

The two consecutive members of the series differ in their molecular formula by a 'CH2' group.

Some important characteristics of the

homologous series All the members conform to a general molecular

formula and have a similar functional group. Each consecutive member differs in the molecular

formula by a unit of 'CH2'. All the members of the series exhibit similar

properties, but the extent of the reactions vary with increasing relative molecular mass.

The physical properties, such as solubility, melting point, boiling point, specific gravity etc. show a gradual change with the increase in their relative molecular masses

Homologous series of Alkanes

IUPAC Names

With the large growth of carbon compounds, it was necessary to name these compounds in a more systematic way. A committee called the 'International Union for Pure and Applied Chemistry' (IUPAC) put forward a system of giving proper scientific names to carbon based compounds. The names derived by their rules are the names followed all over the world and in short are called IUPAC names.

In this system the name of a carbon compound has three main parts as mentioned below:

Wood Root This denotes the number of carbon atoms present in a given molecule.

For e.g., C1-Meth, C2- Eth, C3 - Prop, C4- But. Suffix The suffix denotes the type of bonds or the functional group present in

the carbon chain, e.g. Type of bondFunctional group'ane' (single bond)'ol' for alcohols (-

OH)'ene' (double bond)'al' for aldehydes (-CHO)'yne' (triple bond)'oic acid' for carboxylic acid (-COOH)

IUPAC Names

Functional group Secondary suffix Functional group Secondary

suffix

Alcohols (-OH) -ol Aldehydes (-CHO) -al

Ketones (>C=O) -one Carboxylic acids (-COOH) -oic acid

Amines (-NH2 ) -amine Acid amides (-CONH2 ) -amide

Acid chlorides (-COCL) -oyl chloride Esters (-COOR) -oate

Nitrites (-C=N) -nitrite Thioalcohols (-SH) -thiol

Nomenclature of compounds having polyfunctional groups

When an organic compound contains two or more functional groups, one group is called the principal functional group while the others are called the secondary functional groups and are treated as substituents: The order of preference for principal group is: Carboxylic acid > acid anhydrides > esters > acid halides > amides > nitrites > aldehydes > ketone > alcohols > amines > double bond > triple bond

When the functional groups act as substituents, they ar named as:

Functional groupPrefixFunctional groupPrefix- COOHCarboxy-CHOFormyl-COORAlkoxy cabonyl or Carbalkoxy>COOxo or Kelo-COCLChloroformyl-OHHydroxy-CONH2 Carbamoyl-SHMecaplo-CNCyano-NH2 Amino-ORAkoxy=NHImino

Functional group

Prefix Functional group

Prefix

- COOH Carboxy -CHO Formyl

-COOR Alkoxy cabonyl or Carbalkoxy

>CO Oxo or Kelo

-COCL Chloroformyl -OH Hydroxy

-CONH2 Carbamoyl -SH Mecaplo

-CN Cyano -NH2 Amino

-OR Akoxy =NH Imino

-X Halo -NO2 Nitro

For e.g., the following compound can be named as:

Word root: But (C4) Prefix: 3, chloro Suffix: -ol Name: 3-chloro butanol

Trivial Names, IUPAC Names and Molecular Formula of some Organic Compound

Trivial name IUPAC names Formula

Methane Methane

Ethane Ethane

Ethylene Ethene

Acetylene Ethyne

Formaldehyde Methanal

Acetaldehyde Ethanal

Formic acid Methanoic acid

Acetic acid Ethanoic acid

ABOUT CARBON

Carbon is the sixth most abundant element in the cosmos, yet its abundance in the earth's crust does not even make it among the top ten elements on our planet. There are more known chemical compounds of carbon than any other element except for oxygen and hydrogen. Carbon composes compounds with diverse properties such as graphite and diamond, as well as the recently discovered Buck Minster Fullerenes, or buckyballs. Carbon plays a critical role on Earth as the "stuff" that Life is made from. Every living cell, plant or animal contains carbon. Even in its pure, elemental form carbon is very versatile. 

Carbon : Here…there…and everywhere… Graphite is found in large deposits in Sri Lanka, Malagasy Republic, the former USSR, South Korea, Mexico, and Czechoslovakia. Economic deposits at Val Chisone (Italy). Small hexagonal crystals in marble at Ogdensburg, New Jersey (USA) and in gneiss at Edison, New Jersey (USA). 

Natural: It is formed in high-grade metamorphic rocks as a final product of the carbonisation of organic materials. It is probably also a primary magmatic substance in some pegmatite's and hydrothermal veins. 

Synthetic: Coke is a graphite product that is about 94% carbon. It is produced by heating soft coal in an oven that has no access to air. Most of the impurities sublime off, leaving fairly pure carbon.

Carbon : Here…there…and everywhere… Graphite is found in large deposits in Sri Lanka, Malagasy Republic, the former USSR, South Korea, Mexico, and Czechoslovakia. Economic deposits at Val Chisone (Italy). Small hexagonal crystals in marble at Ogdensburg, New Jersey (USA) and in gneiss at Edison, New Jersey (USA). 

Natural: It is formed in high-grade metamorphic rocks as a final product of the carbonisation of organic materials. It is probably also a primary magmatic substance in some pegmatite's and hydrothermal veins. 

Synthetic: Coke is a graphite product that is about 94% carbon. It is produced by heating soft coal in an oven that has no access to air. Most of the impurities sublime off, leaving fairly pure carbon.

Diamond: Splendid crystals of Diamond occur in the kimberlites of South Africa, Yakutia (former USSR), Murfreesboro, Arkansas (USA), Brazil, Zaire, Sierra Leone and Ghana. Small, nongem-quality crystals are found in Brazil, Venezuela, Zaire and other countries. 

Natural: It is formed in ultramafic rocks, especially kimberlite breccias, and in detrital sedimentary deposits derived from them, in river and marine placers. A rare form of hexagonal "diamond" known as Lonsdaleite is found in certain meteorites, such as those from Canyon Diablo, (USA). 

Synthetic: Most industrial-grade diamonds are produced, with the aid of catalysts, by subjecting high-grade graphite to extremely high temperature and mechanical pressure over a period of several days or weeks. Dr. Guy Suits of the General Electric Company synthesized the first man-made diamonds in 1957. 

INTRODUCTION

In 1985 the carbon structure family was completed by a new modification of pure carbon. With the discovery of the fullerenes by Curl, Smalley and Kroto [1] and additionally with the possibility for the production of fullerenes in large amounts shown by Krätschmer and Huffman [2] in 1990 the scientific competition in experimental and theoretical research was started.

Fullerenes are polyeders build up by n three times coordinated carbon atoms with 12 pentagons and (n) hexagons, were the minimum for n equal 20 is. Fullerenes fulfil the EULER's theorem, were a polyeder build up from pentagons and hexagons has to contain exact 12 pentagons, to build a closed structure. Following this rule, the dodekaeder with 20 carbon atoms is the smallest possible fullerene. Actual the smallest fullerene is the C60, because

important for the stability of the structure is, that no pentagons are side by side. This is described by the Isolated Pentagon Rule (IPR). If two pentagons are annulled, the tension of the binding is increasing and the structure is not anymore energetic stable.

CHEMICAL AND PHYSICAL PROPERSTIES

The carbon atoms in fullerenes are spm (m=2...3). The free valence electrons on the cage building a strong localized π-electron system. This π-electron system influences chemical reactions of the fullerenes. In chemical reactions fullerenes are not reacting aromatic ("super benzene"), they show aliphatic behaviour.

Good solvents for fullerenes are CS2, o-dichlorobenzene, toluene and xylene [7, 8, 9]. Fullerenes are insoluble in water and stabile at air. Thin layers of fullerenes are coloured from yellow to yellow-green.

Because of ππ*-electron transitions solutions of

fullerenes are coloured [10]: - C60 purple/violet red

- C70 brick-red

- C76 light yellow-green

- C2v-C78 maroon, D3-C78 golden,

- C84 brown and

- C86 olive-green.

By heating fullerenes without air up to 1500 °C they transform to graphite. These fullerenes were discovered in 1985 and after solid phase research they have been found in geological material and in the flames of candles.

SPECIES OF FULLERENES

Following species of fullerenes are known: - fullerenes - fullerites [11] - fullerides [11] - endohedral fullerenes - exohedral fullerenes - heterofullerenes [12, 13] - metcars.

Professors Curl and Smalley of the United States and Professor Sir Kroto from the United Kingdom were awarded the Nobel Prize in chemistry in 1996 for the discovery of the buckyball.

The discovery in 1985 of

buckminsterfullerene opened a new era for the chemistry of carbon and for novel materials. The Japanese Sumi Ijima discovered Nanotubes in 1991. The Nanotubes synthesised in the laboratory showed remarkable mechanic properties as well as thermal conductivity and resistance to flame. These Nanotubes consist of layers of graphite in the form of cylinders and often closed at both ends. They can exist as single and multi walled Nanotubes. Normally their diameter is only a few nanometres and their length a millimetre

*Nanotubes (a) armchair (b) zag zag (c) chiral

Nanotubes can be obtained by mixing the soot of

Nanotubes of carbon in water and surfactant. This viscous solution is rotated in a substance capable of aggregating the Nanotubes. A liquid is then injected to aid the formation of a rectangular section, which rolls itself into a cylinder and thus forms carbon Nanotubes.  Another method is to decompose methane with a catalyst. The enlargement of the basal plans of graphite on existing surfaces causes Nanotubes without extremities to extend and l’epaissement the tubes. These tubes are semi-conductors or metallic conductors depending on small variations of their angle of curvature or diameter. This angle defines the type of Nanotubes (armchair, zig zag or chiral) and it is determined by the way the layers of graphite wrap around and interact with themselves. Their properties of conduction depend on their diameter and the way they are helicoidal. Nanotubes are tested with scanning tunnelling microscopy at low temperatures, and a measure of their electronic and physical structure. Even with Nanotubes made by different methods, the results are complimentary and confirm that the conduction is only in one dimension.

Furthermore, fullerenes are very important in

pharmaceutical applications. Wudl synthesised a derivative of a fullerene which is soluble in water. It seems to inhibit the activity of HIV and could be used in a medicine for the treatment of AIDS. Nanotechnology is thus a domain of central importance, at the forefront of chemistry, physics, engineering and materials science. Nanotechnology find ways of manipulating atoms and molecules in an effort to construct new materials and different molecular stratagems.

In conclusion, carbon is truly important for chemistry and for life. It is essential that we continue to study the chemistry of carbon to increase understanding of ourselves and our environment and to improve the quality of life.