Carbon is considered as the third most important element, aftre oxygen and hydrogen, for the existence of life on earth. The name Carbon is derived from a latin word 'Carbo' which means coal.
2. GRAPHITE
VERSATILE NATURE OF CARBON
The earth crust contains only 0.02 % carbon which is present as minerals and the atmosphere has 0.03% of carbon dioxide. All the living things are made up of carbon Compounds.
COVALENT BOND IN CARBON
The bonds which are formed by the sharing of an electron is called covalent bonds. And carbon forms covalent bonds as its valency is 4.
SOME EXAMPLED DEPICTING COVALENT BONDING.
1. Formation of hydrogen molecule
The shared pair of electrons contitute a single bond between the two H- Atoms, which is represented by single line between them . (H―H)
2. Fromation of Chlorine molecule.
3. Formation of water molecule.
4. Formation of Oxygen molecule.
The 2 electrons contributed by each oxygen atom give rise to 2 shared pairs of electrons.
Here, a double bond is formed between the 2 atoms of Oxygen.
5. Formation of Nitrogen Molecule.
Thus, 2 nitrogen atom share 3 electrons thus forming a triple bond between 2 nitrogen atoms.
6. Formation of Methane.(CH4)
Methane is a carbon compund which is also called as marsh gas. It is used as fuel and a major component od CNG and Biogas. It is one of the simplest compound formed by the carbon.'
7. Formation of Ammonia(NH3)
8. Formation of Carbon Dioxide.
9. Formation of Sulpher molecule(S8)
DIFFERENCE BETWEEN IONIC AND COVALENT COMPOUNDS
ALLOTROPES OF CARBON.
Allotrop is the property by virtue of which a element exists in more than one form and each form has different physical properties but identical chemical properties.
1. DIAMOND
General Properties:-
-It is colourles transparent substance with extra ordinary brilliance due to its high refractive index.
-It is quite heavy and the hardest substance known.
-It does not conduct electricity but is a good conductor of heat.
Structure:-
It is a giant molecule of carbon atom in which each carbon atom is linked to 4 other carbon atoms by
strong covalent bonds and maiking a three dimensional network structure.
| Structure of Diamond |
Uses
- Due to its hardness it is used as knives for cutting marble, granite and glass.
- It is used for making Jewellary. e.g. Diamond ring.
| Diamond ring |
General Properties
- It is greyish black opaque substance.
- It is lighter than diamond, feels soft, smooth and slippery touch.
- It is good conducter of electricity but not heat.
Structure
A graphite crystal consist of layers of carbonatoms or sheets of carbon atoms. Each carbon atom in
graphite is joined to 3 other carbon atoms by covalant bonds.
| Structure of graphite |
Uses
- It is used as powdered lubricant for the parts of machinery.
- It is used for making electrodes of cell and lead for pencils.
3. FULLERENES
It is the recently discovered allotrope of carbon. It is named after BUCKMINSTER FULLER.
It contains 60 atoms of carbon.
Structure
It's shape is similar to that of football.
| Structure of fullerene |
The estimated no. of carbon compounds known today are about 3 million.
The main reason for huge no. of carbon compounds are
1. Catenation
The property of selflinking of elements mainly C-atoms through covalent bonds to form long, straight
or branched chains of different sizes is called catenation. Carbon shows maximum catenation in the
periodic table.
2. Tetravalency of Carbon
Carbon belongs to group 14 of the periodic table. Its atomic number is 6 and the electronic
configuration is 2, 4. Thus it has 4 electrons in the outermost shell. There it's valency is 4. Thus it is
able to form 4 covalent bonds.
ORGANIC COMPOUNDS
The compounds of carbon except its oxides, carbonates and hydrogen carbonate salts are known as organic compounds. These compounds are initially extracted from natural substance and it was thought that these carbon compounds could only be formed within living system.
In 1828, German chemist Friedrich Wohler accidently prepared urea from ammonium cynate when he was trying to prepare ammonium cynate by heating ammonium sulphate and potassium cynate.
HYDROCARBONS
The organic compounds contain only carbon and hydrogen are called hydrocarbons.
e.g. CH4, C2H6 etc
All other compounds are considered to be derived from them by replacement of one or more hydrogen atoms by other atoms or group of atoms. The major source of hydrocarbon is petroleum.
The hydrocarbons can be classified as
1. Saturated hydrocarbons
2. Unsaturated Hydrocarbons
SATURATED HYDROCARBONS
The hydrocarbons in which all the carbon atoms are linked with only single bonds. They are also called Alkanes or paraffins.
The general formula of these compounds is CnH2n+2 where, n = number of carbon atoms in one molecule of hydrocarbon.
e.g. methane(CH4), ethane (C2H6) etc
These compounds are chemically inert. i.e. less reactiveand burn with blue flame and non- smoky flame due to their complete combustion. These compounds generally show substitution reaction.
UNSATURATED HYDROCARBON
Those carbon compounds in which atleast one double or triple bond is present alongwith single bonds are called unsaturated hydrocarbons.
These compounds generally burn with sooty flame due to their incomplete combustion. These are more reactive than saturated hydrocarbon and generally undergo addition reaction.
They are classified into 2 types.
1. Alkenes or Olefins
Those carbon compound which have atleast one double bond.
General formula is CnH2n
e.g methene, ethene etc
2. Alkynes
Those carbon compounds which have one or more triple bond in them.
General formula is CnH2n-2
e.g. Methyne, ethyne etc.
HOW TO DRAW THE STRUCTURE OF SATURATED AND UNSATURATED HYDROCARBONS.
STEP 1. First connect all the carbon atoms by single bond.
STEP 2. After that use the hydrogen atoms to satisfy the remaining valencies of carbon.
STEP 3. If number of available H- atoms are less than what is required, satisfy the remaining valencies
by using double or triple bonds.
1. STRUCTURE OF ETHANE (C2H6)
2. STRUCTURE OF PROPANE (C3H8)
3. STRUCTURE OF ETHENE (C2H4)
Step 2. If the compound is saturated, add suffix 'ane' to the root word, but if it is unsaturated add suffix 'ene' and 'yne' for the double and triple bond respectively.
Step 3. If functional group is present in the compound, it is indicated in the name of the compound with either a prefix or suffix.
Carbon belongs to group 14 of the periodic table. Its atomic number is 6 and the electronic
configuration is 2, 4. Thus it has 4 electrons in the outermost shell. There it's valency is 4. Thus it is
able to form 4 covalent bonds.
ORGANIC COMPOUNDS
The compounds of carbon except its oxides, carbonates and hydrogen carbonate salts are known as organic compounds. These compounds are initially extracted from natural substance and it was thought that these carbon compounds could only be formed within living system.
In 1828, German chemist Friedrich Wohler accidently prepared urea from ammonium cynate when he was trying to prepare ammonium cynate by heating ammonium sulphate and potassium cynate.
HYDROCARBONS
The organic compounds contain only carbon and hydrogen are called hydrocarbons.
e.g. CH4, C2H6 etc
All other compounds are considered to be derived from them by replacement of one or more hydrogen atoms by other atoms or group of atoms. The major source of hydrocarbon is petroleum.
The hydrocarbons can be classified as
1. Saturated hydrocarbons
2. Unsaturated Hydrocarbons
SATURATED HYDROCARBONS
The hydrocarbons in which all the carbon atoms are linked with only single bonds. They are also called Alkanes or paraffins.
The general formula of these compounds is CnH2n+2 where, n = number of carbon atoms in one molecule of hydrocarbon.
e.g. methane(CH4), ethane (C2H6) etc
These compounds are chemically inert. i.e. less reactiveand burn with blue flame and non- smoky flame due to their complete combustion. These compounds generally show substitution reaction.
UNSATURATED HYDROCARBON
Those carbon compounds in which atleast one double or triple bond is present alongwith single bonds are called unsaturated hydrocarbons.
These compounds generally burn with sooty flame due to their incomplete combustion. These are more reactive than saturated hydrocarbon and generally undergo addition reaction.
They are classified into 2 types.
1. Alkenes or Olefins
Those carbon compound which have atleast one double bond.
General formula is CnH2n
e.g methene, ethene etc
2. Alkynes
Those carbon compounds which have one or more triple bond in them.
General formula is CnH2n-2
e.g. Methyne, ethyne etc.
HOW TO DRAW THE STRUCTURE OF SATURATED AND UNSATURATED HYDROCARBONS.
STEP 1. First connect all the carbon atoms by single bond.
STEP 2. After that use the hydrogen atoms to satisfy the remaining valencies of carbon.
STEP 3. If number of available H- atoms are less than what is required, satisfy the remaining valencies
by using double or triple bonds.
1. STRUCTURE OF ETHANE (C2H6)
Structure of Ethane
2. STRUCTURE OF PROPANE (C3H8)
STRUCTURE OF PROPANE |
4. STRUCTURE OF PROPYNE (C2H2)
HOW TO DRAW STRUCTURE OF CYCLIC COMPOUNDS
STEP 1 . First connect the available carbon atoms by single bond in cyclic form
STEP 2 . Try to satisfy the tetravalency of eac carbon atom with the available hydrogen.
STEP 3 . Now check the vallency of each carbon. If it is found unsatisfied, use double or triple bond to
satisfy it.
e.g.
Cyclohexane(C6H12)
Benzene (C6H6)
ISOMERISM
Organic compounds with same molecular formula but different chemical and physical properties are called isomers.
The difference in their properties is due to difference in the structers.
e.g. Isomers of PENTANE
FUNCTIONAL GROUPS
Carbon also form bonds with other elements like halogens, oxygen, Nitrogen, Sulpher etc. They are called Hetero - atoms. These atoms or a group of atoms replace one or more hydrogen atom of hydrocarbon. These are also called functional groups.
HOMOLOGOUS SERIES
A series of similarly constituted compounds in which the members present have the same functional group and similar chemical properties and any 2 successive members in a particular differ by a -CH2- unit, is called homologous series.
e.g. CH4, C2H6 etc
Characteristics of a Homologous series.
1. All the members of homologous series can be represented by the same general formula.
2. Any 2 adjacent homologous differ by a 1 carbon atom and 2 hydrogen atoms in their
molecular formula.
3. All the compounds of a homologous series show similar show similar chemical properties.
4. The difference in the molecular masses of any two adjacent homologous or members is 14u.
NOMENCLATURE OF CARBON COMPOUNDS.
Organic compounds have generally two types of names. These are IUPAC names and the common names. The common name are also known as trivial names, have no proper system for naming.
In general, the IUPAC names of organic compounds are based on the name of basic carbon chain modified by a prefix or suffix indicating the name of the functional group.
WRITING IUPAC NAME OF A COMPOUND.
Step 1. Count the number of carbon atoms in the given compound and write the root word for it.
Step 3. If functional group is present in the compound, it is indicated in the name of the compound with either a prefix or suffix.
CHEMICAL PROPERTIES OF CARBON COMPOUNDS
Some of the important chemical properties of carbon compounds are
1. COMBUSTION REACTION
All the carbon compounds burn in oxygen to give carbon dioxide and water vapours. Heat and
light are also released during this process. This is called as combustion.
e.g. C + O2 =====> CO2 + heat + light
2. OXIDATION REACTION
It is the reaction involving the addition of oxygen and removal of hydrogen. Alcohols can be
oxidised by heating them either in presence of of oxidising agents like alkaline KMnO4
(Potassium Permanganate) or acidified K2Cr4O7 (Potassium dichromate).
e.g.
3. ADDITION REACTION
The reaction in which a reagent completely add to a reactant without removal of small molecules
are called addition reaction.
e.g. addition of hydrogen in the presence of catalyst like palladium and nickel, to unsaturated
yields saturated hydrocarbons.
The above reaction is commonly used in the hydrogenation of vegetable oils using nickel a
catalyst.
4. SUBSTITUTION REACTION
The reaction in which a reagent replaces an atom or a group of toms from the reactant are called
substitution reaction. These are generally shown by saturated compounds.
e.g. CH4 + Cl2 ======> CH3Cl + HCl
FUELS AND FLAMES
FUELS
Those carbon compounds which have energy stored in them and burn with heat and light are called fuels. The released energy is utilised for various purposes like cooking etc.
Those fuels which were formed by the decomposition of the remains of pre-historic plants and animals. buried under the earth long time ago are called fossil fuels.
Coal
It is complex mixture of compound of carbon, hydrogen and oxygen and some free carbon alongwith traces of nitrogen and sulpher. It is formed by the decomposition of plants and ferns and trees which got buried under the earth millions of earth of year ago.
Petroleum
It is the dark viscous foul smelling oil and is known as rock oil or black gold. It is formed by the decomposition of the remains of extremely small plants and animals buried under the sea millions of years ago.
FLAMES
A flame is a region where combustion of gaseous substances takes place. Depending upon the amount of oxygen available and burning of fuels, flames are of 2 types.
1. Blue or Non-Luminous flame
When the oxygen supply is sufficient, the fuels burn completely producing a blue flame and no light is produced. e.g. burning of LPG in stove.
2. Yellow or Luminous flame.
In the sufficient supply of air, the fuels burn incompletely and produce yellow flame because of the presence of unburnt carbon particles, e.g. Burning of wax vapours.
SOME IMPORTANT CARBON COMPOUNDS\
Ethanol
Its common name is ethyl alcohol and formula C2H5OH or CH3CH2OH
Preparation
Alcohol is obtained by the fragmentation of molasses which are obtained from sugarcane juice.
Physical properties
It is liquid at room temperature. Its melting point is 156K and boiling point is 351K. It is soluble in water in all proportions.
Chemical Properties.
1. Reaction with sodium
Ethyl alcohol reacts with sodium metal leading to the evolution of hydrogen gas alongwith the formation of sodium ethoxide.
2Na + 2CH3CH2OH =======> 2CH3CH2ONa + H2
2CH3CH2ONa is sodium ethoxide.
2. Dehydration
Removal of water molecules from compound is known as dehydration reaction.
CH3CH2OH ======> CH2CH2 + H2
CH2CH2 is ethene.
Uses of ethanol.
It is used as an active ingredient in all alcoholic drinks.
It is useful in medicines like tincture of iodine cough syrups and many other tonics.
Ethanoic Acid or Acetic acid
It is commonly known as acetic acid. Its formula is CH3COOH.
Physical properties
-Its melting point is 290K
-During winters it often freezes and forms ice like flakes, so it called glacial acetic acid. Glacial acetic acid is a trivial name for water free acetic acid.
-It is weaker acid than HCl but stronger than Alcohols.
Chemical Properties.
1. Reaction with a base
It reacts with a base such as sodium hydroxide to give a salt(Sodium acetate) and water.
CH3COOH + NaOH =====> CH3COONa + H2O
CH3COONa is sodium acetate.
2. Esterification
When ethanol reacts with acetic acid in the presence of an acid as catalyst a fruity smelling liquid
called ester or ethyl ethanoate is obtained. This reaction is called esterification reaction.
The ester gets converted back into alcohol and sodium salt of acid when treated with alkali like
sodium hydroxide. This reaction is called saponification reaction as it is used for the preparation
of soap.
3. Reaction with carbonates and hydrogen carbonates.
CH3COOH + NaHCO3 =====> CH3COONa + H2O + CO2
CH3COOH + Na2CO3 ======> 2CH3COONa + H2O + CO2
USES OF ACETIC ACID
- It is widely used for making vinegar.
- It is widely used as preservative in pickles.
- It is used for the synthesis of other compounds like esters.
SOAPS AND DETERGENTS'
Soaps are sodium or potassium salt of long chain carboxylic acid and have general formula RCOONa
where R= C15H31, C17H35
Detergents are usually ammonium or sulphonate salts of long chain carboxylic acid. They are also called as soapless soap.
Manufacture of Soaps and Detergents
Soaps are made of two parts- along hydrocarbon part (non ionic part) and a short ionic part containing -COONa group. The long hydrocarbon part is hydrophobic and therefore insoluble in water but soluble in oil.
The ionic portion of the soap molecule is hydrophilic so, soluble in water and insoluble in oil.
Cleansing action of soap
Soap molecules have different properties at their two ends, Its one end is hydrophilic and other is hydrophobic. At the surface of water, the hydrophobic end or tail of soap will be insoluble in water with the ionic end in the water and the hydrocarbon tail protruding out of the water.
| Micelle |
Inside water, these molecules show unique orientation that keeps the hydrocarbons portion out of the water. This is done by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and on the surface of cluster, ionic ends are present.
This formation of cluster of molecules is called micelle. To wash away the loosened dirt particles the form of micelles from the surface of the cloth, it is either scrubbed mechanically or beaten or agitated in washing machine.
In the form of a micelle, soap is able to clean, since the only dirt is being collected in the centre of micelle.
Micelle stays as colloids in the solution and does not come closer to precipitate due to ion-ion repulsion. Hence, the dirt suspended in the micelle is also rinsed away.
If you have any doubts regarding this chapter......mention them in comments.
