Structural Isomers:
Componds with the same molecular formula but different structure.

Positional Isomers:
Compounds having the same carbon chain but differ in the position of double bond (which is a characteristic property).

Aromatic Hydrocarbons:
Hydrocarbons containig one or more isolated or fused Benzene Rings. Its general formula is C_nH_2n.

PETROLEUM:
Petroleum is a dark coloured, viscous liquid found deep in the Earth's crust. Chemically, it is a mixture of various types of hydrocarbons along with some oxygen, sulphur and nitrogen containing compounds.

Formation of Petroleum:
Petroleum is believed to be formed by the decay and decomposition of marine as well that of plant materials of the prehistoruc forests. In other words, petroleum, is of animal and plant origin. It is thought that due to some upheveals like earthquake, volcanic erruptions, etc., these prehistoric forests, and sea animals get buried under the Earth's crust. Due to prolonged action of high pressure and high temperature in the interior of the earth for ages, the organic matter decomposed into Petroleum.

Petroleum refining:
The process of separating crude petroleum into useful fractions by fractional distillation is known as refining.

Use of different functions of Petroleum:
• Petroleum Gas: It is used as a fuel.
• Gasoline: It is used as a motor fuel.
• Kerosene: It is used as household and lighting purposes.
• Gas oil and Diesel oil: They are used as furnace fuel and for diesel engines.
• Lubricating oil and Grease: They are used for lubrication.
• Vaseline: They are used for softening skin.
• Asphalt: They are sused for road surfacing.
• Paraffin Wax: They are used for makig candles.

The simplest carbon dioxide removal approach is to plant a tree
- Ken Caldeira

FUNCTIONAL GROUPS:
The heteroatoms and the group attached to the hydrocarbon part forming stable molecule, characterise the specific properties of the compound irrespective of the nature and length of the carbon chain. Hence, these heteroatoms and groups are called functional groups.

Some functional groups:
1. Alcohols - Alcohols are a family of carbon compounds which contain the functional group OH attached to a saturated carbon.
Structure: -OH
General formula: C_nH_2n+1OH
Example: CH₃-CH₂-OH (Ethanol)
2. Aldehydes - Aldehydes are a family of carbon compounds which contain the functional group CHO attached to a saturated carbon.
Structure: -CHO
Example: CH₃-CHO (Ethanal)
3. Ketones - Ketones are a family of carbon compounds which contain the functional group CO attached to a saturated carbon.
Structure: -CO-
Example: CH₃-CO-CH₃ (Propanone)
4. Carboxylic acids - Carboxylic acids are a family of carbon compounds which contain the functional group COOH attached to a saturated carbon.
Structure: -COOH
Example: CH₃-COOH (Ethanoic acid)

Some questions and answers:
Q. What happens when ethanol is burnt in air?
Ans:- When ethanol is burnt in air , carbon dioxide and water are produced with the liberation of energy i.e., heat and light energy.
CH₃-CH₂-OH (ethanol)+ 3O₂ → 2CO₂ + 3H₂O + energy
Q. What happens when ethanlo is oxidised with alkaline potassium permanganate(KMnO₄)?
Ans:- When ethanol is oxidised with alkaline potassium permanganate, ethanal is produced and ethanal is oxidised further to ethanoic acid.

First step:
CH₃CH₂OH (ethanol) + [O] (nascent oxygen) _{(alk. KMnO4)} → CH₃CHO + H₂O (ethanal)
Second step:
CH₃CHO + [O] _{(alk. KMnO4)} → CH₃COOH (ethanoic acid)

Q. What is hydrogenation? Write its one application.
Ans:- Hydrogenation is a process in which the unsaturated hydrocabons add hydrogen in presence of catalyst like palladium, platinum, nickel, etc. to form saturated hydrocabons.
Hydrogenation is used in the manufacture of vegetable ghee from vegetable oil. Example: CH₂=CH₂ (ethene)+ H_{2 (Ni cat.)} → CH₃-CH₃ (ethane)

Q. Explain why the orange colour of Bromine water is discharged when ethene is passed into Bromine water.
Ans:- When ethene/propene is passed into Bromine water, a colourless addition product called 1,2 - Dibromoethane is produced.
CH₂=CH₂ → CH₂Br-CH₂Br (1,2-dibromoethane)
Due to the formation of colourless additio product, orange colour Bromine water is discharged.

Q. Write the physical properties of ethanol, CH₃CH₂OH.
Ans:- The physical properties are:
(i) Ethyl alcohol is a colourless volatile liquid wit a boiling point of 78°C
(ii) It has a typical pleasant smell
(iii) It is miscible with water in all proportions. It is also miscible with many organic solution.

Q. Write the uses of Ethanol.
Ans:- Ethanol mixed wit petrol, is used as a fuel for internal combustion engines. Also, it is used as the solvent for lacquers.

Q. Describe three chemical reactions/properties of ethanol. Ans:- CHemical properties of ethanol:
(i) Reaction with sodium metal: Ethanol reacts with sodium metal to produce sodium ethoide and hydrogen gas.
2CH₃CH₂OH (ethanol) + 2Na → 2CH₃CH₂ONa (sodium ethoxide) + H₂
(ii) Dehydration of ethanol: Ethanol on heating with concentrated sulphuric acid, H₂SO₄ at 170°C, loses a water molecule giving ethene.
CH₃CH₂OH (ethanol) _{(conc. H2SO4/170°C (heat) )} → CH₂=CH₂ + H₂O
(iii) Oxidation of ethanol: Oxidation of ethanol with alkalineKMnO₄ gives ethanoi acid.
First step:
CH₃CH₂OH (ethanol) + [O] (nascent oxygen) _{(alk. KMnO4)} → CH₃CHO + H₂O (ethanal)
Second step:
CH₃CHO + [O] _{(alk. KMnO4)} → CH₃COOH (ethanoic acid)

Q. What is Substitution Reaction?
Ans:- The reaction which involves direct repacement of an atom or a group of atoms in an organic molecule by another atom or group of atoms without any change in the rest of the molecule, is called Substitution Reaction.
Example:
CH₄ (methane) + Cl₂ → CH₃Cl (chloromethane) + HCl
CH₃Cl + Cl₂ → CH₂Cl ₂ (dichloromethane) + HCl
CH₂Cl + Cl₂ → CHCl ₃ (trichloromethane) + HCl (trichloromethane is chloroform)
CHCl₃ + Cl₂ → CCl ₄ (tetrachloromethane) + HCl (tetrachloromethane is carbon tetrachloride)

Q. What is vinegar? Write its uses.
Ans:- Oxidation of fermented liquors which contain about 12-15% ethyl alcohol, with air under the influence of bacteria Mycoderma aceti gives dilute acetic acid solution (containing about 4-7% acetic acid) called vinegar. OR, the dilute acetic acid solution containing about 4-7% acetic acid is called vinegar.
Uses: Vinegar is used as a preservative of pickles and as table food.

Q. Write the physical properties of ethanoic acid.
Ans:- The properties are:
(i) Ethanoic acid is a colourless corrosive liquid with a sharp vinegar odour and sour taste.
(ii) Its freezing point is 16.6°C and boiling point is 118°C.
(iii) It is miscible with water, ether (carbon compounds) and ethanol.

Q. What is esterification Reaction?
Ans:- A reaction between a carboxylic acid and an alcohol producing ester and water is called Esterification Reaction.

Q. How is ethyl acetate obtained?
Ans:- Ethyl acetate is obtained by the reaction of acetic acid and ethyl alcohol in presence of an acid catalyst.
CH₃COOH (acetic acid) + CH₃CH₂OH (ethanol) _{(H ⁺)} → CH₃COOCH₂CH₃ (ethyl acetate) + H₂O
* ethyl acetate is ethyl ethanoate

Q. Write the uses of ethyl acetate?
Ans:- Ethyl acetate is used in making perfumes and as flavouring agents.