CARBON AND ITS COMPOUNDS
Carbon is an element. It is a non-metal. All things, plants, and animals are made up of carbon compounds (called organic compounds). A large number of things that we use in our daily life are made of carbon compounds. Carbon compounds play a very important role in our daily life.
Carbon Always Forms Covalent Bonds
The electronic configuration of carbon is K (2), L (4). It is not possible to remove 4 electrons from a carbon atom to give it the inert gas electron arrangement. Since carbon atoms can achieve the inert gas electron arrangement only by the sharing of electrons, therefore, carbon always forms covalent bonds.
Carbon is Tetravalent
Since one carbon atom requires 4 electrons to achieve the eight-electron inert gas structure, therefore, the valency of carbon is 4.
Self Combination
The most unique property of carbon is its ability to combine with itself, atom to atom, to form long chains. The properties of self-combination of carbon atoms to long chains are useful to us because it gives rise to an extremely large number of carbon compounds (or organic compounds).
Occurrence of Carbon
Carbon occurs in nature in a ‘
- Combined State – carbon dioxide gas, carbonate, petroleum, coal, fats, protein, etc..
Allotropes of Carbon
The various physical forms in which an element can exist can be called allotropes of the element.
The three allotropes of carbon are:
- Diamond
- Graphite, and
- Buckminsterfullerene
Diamond and Graphite
Diamond is a colorless transparent substance having extraordinary brilliance. If we burn diamonds in oxygen then carbon dioxide gas is formed and nothing is left behind. This shows that diamond is made up of carbon only.
Graphite is a grayish-black opaque substance. If we burn graphite in oxygen, then only carbon dioxide gas is formed and nothing is left behind. This shows that graphite is made up of carbon only.
Diamond and graphite, have entirely different physical properties. The difference arises because of the different arrangements of carbon atoms in them.
Structure of Diamond
Each carbon atom in the diamond is linked to four other carbon atoms by strong covalent bonds. The rigid structure of the diamond makes it a very substance. Diamonds are non-conductor of electricity.
Structure of Graphite
Each carbon atom in the graphite layer is joined to three other carbon atoms by strong carbon atoms. Due to the sheet-like structure, graphite is a soft substance. Graphite is a good conductor of electricity due to the presence of free electrons.
Uses of Diamond
- Diamonds are used in cutting instruments like glass cutters and rock drilling equipment.
- Diamonds are used for making jewelry.
Diamonds can be made artificially by subjecting pure carbon to very high pressure and temperature.
Uses of Graphite
- Powdered graphite is used as a lubricant for the fast-moving parts of machinery. It can be used for lubricating those machine parts which operate at very high temperatures.
- Graphite is used for making carbon electrodes or graphite electrodes in dry cells and electric arcs.
- Graphite is used for making the cores of our pencils called ‘pencil leads’ and black paints.
Buckminsterfullerene
Buckminsterfullerene is an allotrope of a carbon-containing cluster of 60 carbon atoms joined together to form spherical molecules. It is a dark solid at room temperature.
ORGANIC COMPOUNDS
The compounds of carbon are known as organic compounds. Carbon compounds (or organic compounds) are covalent compounds having low melting points and boiling points. Most of the carbon compounds are non-conductor of electricity. Organic compounds occur in all living things like plants and animals.
Though oxides of carbon like carbon monoxide and carbon dioxides are also carbon compounds they are not considered to be organic compounds.
Reason for the large number of organic compounds
- One reason for the existence of a large number of organic compounds or carbon compounds is that carbon atoms can link with one another by means of covalent bonds to form long chains of the carbon atom.
- Another reason for the existence of a large number of organic compounds or carbon compounds is that the valency of carbon is 4.
HYDROCARBONS
A compound made up of hydrogen and carbon only is called hydrocarbon. The most important natural source of hydrocarbons is petroleum.
Types of hydrocarbons
- Saturated hydrocarbons (Alkanes)
A hydrocarbon in which one carbon atom is connected by only a single bond is called a saturated hydrocarbon. The general formula of saturated hydrocarbons or alkanes is CnH2n+2 where n is the number of carbon atoms in one molecule of alkane.
- Unsaturated Hydrocarbons (Alkenes and Alkynes)
A hydrocarbon in which the two carbon atoms are connected by a ‘double bond’ or a ‘triple bond’ is called an unsaturated hydrocarbon.
(i) Alkenes
An unsaturated hydrocarbon in which two carbon atoms are connected by a double bond is called an alkene. The general formula of an alkene is CnH2n where n is the number of carbon atoms in its one molecule.
(ii) Alkynes
An unsaturated hydrocarbon in which the two carbon atoms are connected by a triple bond is called an alkyne. The general formula of alkynes is CnH2n-2 where n is the number of carbon atoms in one molecule of the alkynes.
Alkyl Groups
The group formed by the removal of one hydrogen atom from an alkane molecule is called the alkyl group.
CYCLIC HYDROCARBONS
- A saturated cyclic hydrocarbon is ‘cyclohexane’
The formula of cyclohexane is C6H12. A molecule of cyclohexane contains 6 carbon atoms arranged in a hexagonal ring with a carbon atom having 2 hydrogen atoms attached to it. The cycloalkane having 3 carbon atoms in the ring is called cyclopropane (C3H6). The cycloalkane with 4 carbon atoms in the ring is called cyclobutane (C4H8).
- An unsaturated cyclic hydrocarbon is ‘benzene’
The formula of benzene is C6H6 . A carbon atom has 3 carbon-carbon double bonds and 3 carbon-carbon single bonds arranged in a hexagonal ring. It has also 6 carbon-hydrogen single bonds.
NAMING OF HYDROCARBONS
- The number of carbon atoms in hydrocarbon is indicated by using the following stems:
One carbon atom—‘Meth’
Two carbon atoms—‘Eth’
Three carbon atoms—‘Prop’
Four carbon atoms—‘But’
Four carbon atoms—‘But’
Five carbon atoms—‘Pent’
Six carbon atoms—‘Hex’
Seven carbon atoms—‘Hept’
Eight carbon atoms—‘Oct’
Nine carbon atoms—‘Non’
Ten carbon atoms—‘Dec’
- A saturated hydrocarbon containing single bonds is indicated by writing the word ‘ane’ after the stem.
- An unsaturated hydrocarbon containing a double bond is indicated by writing the word ‘ene’ after the stem.
- An unsaturated hydrocarbon containing a triple bond is indicated by writing the word ‘yne’ after the stem.
IUPAC Nomenclature for branched-Chain Saturated Hydrocarbons
1. The longest chain of carbon atoms in the structure of the compound is found first. The compound has then named a derivative of the alkane hydrocarbon which corresponds to the longest chain of carbon atoms.
2. The alkyl groups present as sight chains are considered constituents and named separately as methyl (CH3-) or ethyl (C2H5-) groups.
3. The carbon atoms of the longest carbon chain are numbered in such a way that the alkyl groups get the lowest possible number.
4. The position of an alkyl group is indicated by writing the number of the carbon atoms to which it is attached.
5. The IUPAC name of the compound is obtained by writing the ‘position and name of alkyl group’ just before the name of the ‘parent hydrocarbon’.
ISOMERS
Organic compounds having the same molecular formula but different structures are known as isomers. Isomerism is possible only with hydrocarbons having 4 or more carbon atoms. No isomerism is possible in methane, ethane, and propane. Two isomers of the compound butane (C4H10) are possible. Three isomers of the compound pentane (C5H12) are possible.
HOMOLOGOUS SERIES
A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group.
Characteristics of a Homologous Series
- All the members of a homologous series can be represented by the same general formula.
- Any two adjacent homologous differ by 1 carbon atom and 2 hydrogen atoms in their molecular formula.
- The difference in the molecular masses of any two adjacent homologous is 14u.
- All the compounds of a homologous series show similar chemical properties.
- The members of a homologous series show a gradual change in their physical properties with an increase in the molecular formula.
FUNCTIONAL GROUPS
An ‘atom’ or a group of atoms that makes a carbon compound reactive and decides its properties (or function) is called a functional group.
1. Halo group: -X (X can be Cl, Br or I)
The halo group can be, -Cl; Bromo, -Br; or do, -I, depending upon whether a chlorine, bromine, or iodine atom is linked to a carbon atom of the organic compound. The Halo group is also known as the halogen group.
2. Alcohol Group: -OH
The alcohol group (-OH) is known as the alcoholic group or hydroxyl group. The compounds containing the alcohol group are known as alcohols. Example - methanol CH3OH, ethanol C2H5OH.
3. Aldehyde Group: -CHO
In the aldehyde group, the H atom is attached by a single bond and the O atom is attached by a double bond with a carbon atom. The compounds containing the aldehyde group are known as aldehydes. Examples – are methane HCHO, and ethane CH3CHO.
4. Ketone Group: -CO-
The group is known as a ketonic group. The compounds containing the ketonic group are known as ketones. Examples are: propanone, CH3COCH3, and butanone, CH3COCH2CH3
5. Carboxylic Acid Group: -COOH
The carboxylic acid group is known as the carboxylic group or an organic group. The organic compound containing the carboxylic acid group is known as carboxylic acid or organic acid.
6. Alkene Group:
The alkene group is a carbon-carbon double bond. Examples: ethane, propene.
7. Alkyne Group:
The alkyne group is a carbon-carbon triple bond. Examples: ethyne, propyne.
All organic compounds having the same functional group show similar chemical properties.
HALOALKANES
When one hydrogen atom is replaced by a halogen atom, haloalkane is formed.
Replace one H with Cl
CH4 à CH3Cl
Methane Cloromethane
The general formula of haloalkane is CnH2n+1-X (where X represents Cl, Br, or I).
ALCOHOLS
The hydroxyl group attached to a carbon atom is known as the alcohol group.
Replace H with OH
CH4 à CH3-OH
Methane Methanol
The general formula of alcohols is CnH2n+1-OH.
In the naming of alcohols by the IUPAC method, the last ‘e’ of the parent ‘alkane’ is replaced by ‘ol’ to indicate the presence of the OH group.
ALDEHYDES
Aldehydes are carbon compounds containing an aldehyde group attached to a carbon atom. The general formula of aldehydes is CnH2nO.
In the IUPAC method, the last ‘e’ is replaced by ‘al’ to indicate the aldehyde group.
KETONES
The simplest ketone contains three carbon atoms in it. The general formula of the ketone is CnH2nO. C3H6O is written as CH3COCH3.
In naming the ketones by the IUPAC method, the last ‘e’ of the parent alkane is replaced by ‘one’ to indicate the presence of the ketone group.
CARBOXYLIC ACIDS
The general formula of a carboxylic acid is R-COOH where R is the alkyl group. Formic acid HCOOH is the simplest carboxylic acid.
The IUPAC name of an organic acid is obtained by replacing the last ‘e’ of the parent alkane with ‘oic’ and adding the word ‘acid’ to the name thus obtained.
COAL AND PETROLEUM
When a fuel is burned, the energy is released mainly as heat. Most of the fuels are obtained from coal, Petroleum, and natural gas.
Coal is a complex mixture of compounds of carbon, hydrogen, and oxygen, and some free carbon. Small amounts of nitrogen and sulfur compounds are also present in coal.
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
1. Combustion (or Burning)
The process of burning a carbon compound in the air to give carbon dioxide, water, heat, and light, is known as combustion. Alkanes burn in the air to produce a lot of heat due to which alkanes are excellent fuels.
CH4 + 2O2 à CO2 + 2H2O + Heat + Light
The saturated hydrocarbons, carbon, and their composition are used as fuels because they are in the air releasing a lot of heat energy.
The saturated hydrocarbons burn in the air with a blue, non-sooty flame. If however, the supply of air for burning is reduced, then incomplete combustion of even saturated hydrocarbons takes place and they burn to produce a sooty flame.
The unsaturated hydrocarbons burn in the air with a yellow, sooty flame. If unsaturated hydrocarbons are burned in pure oxygen, then they will burn completely producing a sooty flame.
2. Substitution Reaction
The reaction in which one hydrogen atom of a hydrocarbon is replaced by some other atoms is called a substitution reaction. Substitution reactions are a characteristic property of saturated hydrocarbons or alkanes.
Saturated hydrocarbons undergo substitution reaction with chlorine in presence of sunlight.
CH4 + Cl2 à CH3Cl + HCl
3. Addition Reaction
Addition reactions (like the addition of hydrogen, chlorine, or bromine) are characteristic properties of unsaturated hydrocarbons. Addition reactions are given by all the alkenes and alkynes.
Ethene reacts with hydrogen when heated in presence of nickel to form ethane.
CH2═CH2 + H2 à CH3-CH3
The addition of hydrogen to an unsaturated hydrocarbon is called hydrogenation.
Some Important Carbon Compounds
ETHANOL
The common name of ethanol is ethyl alcohol. Ethanol is a neutral compound. It has no effect on any litmus solution.
Chemical properties
1. Combustion
Ethanol burns in the air to form carbon dioxide and water vapor, releasing a lot of heat and light.
C2H5OH + 3O2 à 2CO2 + 3H2O + heat + light
2. Oxidation
When ethanol is heated with an alkaline potassium permanganate solution it oxidized to ethanoic acid.
CH3CH2OH + 2[O] à CH3COOH + H2O
3. Reaction with sodium metal
Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas.
2C2H5OH + 2Na à 2C2H5O-Na+
4. Dehydration
When ethanol is heated with an excess concentrated sulphuric acid it gets dehydrated to form ethane:
CH3-CH2OH à CH2═CH2 + H2O
5. Reaction with Ethanoic Acid
Ethanol reacts with ethanoic acid on warming in presence of concentrated sulphuric acid to form an ester, ethyl ethanoate.
CH3COOH + C2H5OH à CH3COOC2H5 + H2O
ETHANOIC ACID
The common name of ethanoic acid is acetic acid.
Chemical Properties
1. Action on Litmus
Ethanoic acid is acidic in nature. It turns blue litmus paper to red.
2. Reaction with Carbonate
Ethanoic acid reacts with sodium carbonate to form sodium ethanoic and carbon dioxide
CH3COOH + NaHCO3 à CH3COONa + CO2 + H2O
3. Reaction with Hydrogencaronate
Ethanoic acid reacts with sodium hydrogen carbonate to form carbon dioxide
CH3COOH + NaHCO3 à CH3COONa + CO2 + H2O
5. Reaction with sodium hydroxide
Ethanoic acid reacts with bases to form salts and water.
CH3COOH + NaOH à CH3COONa + H2O
SOAPS
Soap is the sodium salt of a long-chain carboxylic acid which has cleansing properties in water. Examples of the soaps are sodium stearate (C17H35COO-Na+) and sodium palmitate (C15H31COO-Na+).
Structure of Soap Molecule:-
A soap molecule is made up of two parts: a long hydrocarbon part and a short ionic part containing the –COO-Na+ group.
The hydrocarbon part of the soap molecule is soluble in oil or grease, so it can attach to the oil and grease particles present on dirty clothes. The ionic part of the soap molecules is soluble in water, so it can attach to the water particles. A ‘spherical aggregate of soap molecule’ is called a ‘micelle’. Micelle formation takes place when soap is added to water because the hydrocarbon chains of soap molecules are hydrophobic (water repelling) which are insoluble in water, but the ionic ends of soap molecules are hydrophilic (water-attracting) and hence soluble in water.
DETERGENTS
Detergents are also called ‘soap-less soaps’ because though they act like soap in having cleansing properties, they do not contain the ‘soap’ like sodium stearate, etc.
A detergent is the sodium salt of a long-chain benzene sulphonic acid which has cleansing properties in water. Examples are: CH3-(CH2)11-C6H4-SO3-Na+ (sodium n-dodecyl benzene sulphonate), and CH3-(CH2)10-CH2-SO4-Na+ (sodium n-dodecyl sulphate). The cleansing action of a detergent is similar to that of salt.
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