chemistry class 10 notes chapter 11 ORGANIC CHEMISTRY
Q.1: What is the vital force theory?
Ans: Vital force theory:
This theory was presented by a Swedish Chemist, Berzelius in 1815. According to this theory, organic compounds cannot be prepared in the laboratory. They are only prepared in the bodies of living organisms under the influence of a supernatural force called vital force.
Urea (from urine), tartaric acid (from grapes), citric acid (from the lemon) and sucrose (from cane sugar) are organic compounds.
Rejection of vital force theory:
In 1828, a German chemist Friedrich Wohler prepared an organic compound (urea) in the laboratory by heating ammonium cyanate and rejected the vital force theory.
Q.2: Why organic compounds are placed in a separate branch of chemistry?
Ans: Reason for placing organic compounds in a separate branch of chemistry:
The organic compounds have common properties and they are very large in number. Thus, to make their study easier they are placed in a separate branch of chemistry called organic chemistry.
Q.3: Which compounds of carbon are not organic?
Ans: The following compounds of carbon are not included in organic compounds because they do not possess the properties of organic compounds;
- Carbonates like sodium carbonate, potassium carbonate calcium carbonate etc.
- Bicarbonates: like sodium bicarbonate, magnesium bicarbonate, calcium bicarbonate etc.
- Cyanides: like potassium cyanide, sodium cyanide, magnesium cyanide etc.
- Carbides like calcium carbide, aluminium carbide etc.
- Carbon monoxide:(CO)
- Carbon dioxide: CO2
- Sulphide like carbon disulphide
Q.4: Define organic compounds and organic chemistry?
Ans. Organic compounds:
“The compounds of carbon and hydrogen called hydrocarbons. Hydrocarbons and their derivatives are called organic compounds.” Composition of organic compounds:
All organic compounds contain carbon and hydrogen as an essential ingredient besides these elements they may also contain halogens, sulphur, oxygen, nitrogen.
Derivatives of hydrocarbon:
When hydrogen atom of a hydrocarbon is replaced by an atom or group of atoms then the resulting compound will be the derivative of that hydrocarbon.
If we remove one H from ethane C2H6 then ethyl group(C2H5) is obtained thus ethyl alcohol(C2H5OH), ethyl chloride(C2H5CI), ethyl bromide(C2H5Br) are the examples of derivatives of ethane.
“The branch of chemistry which deals with the study of hydrocarbons and their derivatives is called organic chemistry.” For example, in this branch, we study about alkanes like methane, alcohols like ethyl alcohol etc.
Q.5: How organic compounds are represented by
- Molecular formula
- Structural formula
- Condensed formula
- Dot and cross formula
“Molecular formula shows the actual number of atoms in a molecule of an organic compound.”
I Molecular Formula
2. Structural Formula:
“This formula represents the arrangement of different atoms of carious elements around the carbon atoms present in a molecule of a compound.”
The structural formula shows the nature and type of atoms present in a molecule of a compound. It also shows the bonding arrangement of atoms.
In the structural formula, single bonds are shown by a single dash (— ), double bond by double dashes ( =) and a triple bond by triple dashes(= ) ( between the bonded atoms.
Structural formulas of some compounds are given below:
3. Condensed Formula:
In this formula group of atoms are shown in an order with no bonds dashes.
- For example, hexane (C81-114) has the condensed formula of CH3(CH2)4CH3
- The condensed formula of heptane (C7H16) is CH3(CH2)5CH3
4. Dot and Cross Formula / Electronic formula:
The type of formula in which electrons are represented in the form of dots and cross of an organic compound is called Dot and cross Formula e.g.
Q.6: Describe the classification of organic compounds. Ans: Classification Of Organic Compounds:
The classification of organic compounds is given below:
- On the basis of the carbon skeleton
- On the basis of bonds
The detail is given below:
1. On the basis of carbon skeleton:
On the basis of the carbon skeleton, organic compounds have the following two types:
- Open chain organic compounds
- Close chain or cyclic organic compounds
2.Open chain organic compounds:
“The type of organic compounds which consist of an open chain of carbon atoms are called open-chain organic compounds or aliphatic organic compounds.”
Open chain organic compounds are further classified into two types which are given below:
A. Straight chain organic compounds:
“The type of open chain organic compounds which contain a straight chain of carbon in their molecules are called straight-chain organic compounds.”
A carbon atom in straight-chain organic compounds is not directly bonded to more than two carbon atoms. The prefix n is put before their names which means “normal.”
Some examples of straight-chain organic compounds are given below:
- CH3— CH3—CH2—CH3 (n-butane)
- CH3— CH2— CH2— CH2— CH3 (n-pentane)
- CH3—CH2 —CH2 —CH2—CH2 —CH3(n-hexane)
B. Branched-chain organic compounds:
“The_ type of open chain organic compounds which contains branches of carbon atoms is called branched-chain organic compounds.”
At least one carbon atom in their molecules is directly bonded to more than two carbon atoms. Their common names have prefix iso- with a corresponding organic compound.
ii. Close chain or cyclic organic compounds:
“The type of organic compound in which the carbon atoms are linked in cyclic form or ring form is called a cyclic organic compound.”
For cyclic form, at least three carbon must be present.
These are further classified into two types:
- Homocyclic or carbocyclic organic compounds
- Heterocyclic organic compounds
A. Homocyclic or carboxylic organic compounds:
The type of cyclic organic compounds in which the ring is composed of carbon atoms only is called homocyclic or carboxylic organic compounds.
These have further two types:
- Ali-cyclic organic compounds
- Aromatic organic compounds
1. Ali-cyclic organic compounds;
These are the type of homocyclic organic compounds in which the carbon ring do not have alternate double and single bonds(aromatic character). They resemble the open-chain organic compOunds in their properties but differ from them in their formula. They differ from their corresponding open-chain member by H2 group.
Examples of Ali-cyclic organic compounds are given below:
ii. Aromatic organic compounds:
These are the type of hemicyclic organic compounds in which the carbon rings have alternate double and single bonds. The important member of this class is benzene and the compounds derived from benzene.
Some examples of aromatic organic compounds are given below:
B. Heterocyclic organic compounds:
The type of cyclic organic compounds in which the ring contain other atoms like nitrogen, sulphur etc. along with carbon is called heterocycle organic compounds.
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