Carbon and its Compounds Class 10 Notes Science Chapter 4

Chapter at a Glance

1.Introduction
Bonding in carbon: Carbon form covalent bonds. Covalent bond formation involves sharing of electrons between bonding atoms which may be either same or different.
Covalency: The number of electrons contributed by an atom for sharing is known as its covalency.

Characteristics of covalent compounds
(i) These compounds are molecular in nature (i.e. they exist as single molecules).
(ii) These are insoluble in water and soluble in benzene, kerosene and petrol etc.
(iii) These compounds are poor conductor of electricity.

2. Allotropy in carbon
The property due to which an element exists in two or more forms, which differ in their physical and some of the chemical properties is known as “allotropy” and the various forms are called “allotropes”.
Carbon exists in two allotropic form- crystalline and amorphous. The crystalline forms are diamond and graphite whereas the amorphous forms are coal, charcoal, lamp black etc.
Fullerenes form another class of carbon allotropes. The first one to be identified was C-60, which has carbon atoms arranged in the shape of a football.

3. Catenation: The property of elements to form long chains or rings by self linking of their own atoms through covalent bonds is called catenation. The extent of catenation depends upon the strength of the bonds between the atoms involved in catenation.

4. Saturated and unsaturated carbon compounds
In saturated compounds the valencies of all the carbon atoms are satisfied by single bonds between them. While in unsaturated compounds, the valencies of all the carbon atoms are not satisfied by single bonds, thus in order to satisfy their valencies, they form double or triple bond between the carbon atoms.

Straight chain compounds: The compounds which contain straight chain of carbon atoms, e.g., normal butane (C4H10), normal pentane (C5H12) etc.
Branched chain compounds: The compounds which contain branched
chain of carbon atoms, e.g., isobutane (C4H10), isopentane (C5H12), neopentane (C5H12) etc.
Closed chain compounds or ring compounds: Cyclic compounds are
called closed chain or ring compounds e.g., cyclohexane (C6H12), cyclopentane (C H ), cyclobutane (CH), cyclopropane (CH) etc.

5. Hydrocarbons: All those compounds which contain just carbon and hydrogen are called hydrocarbons.

6. Functional group: The atom or group of atoms which determine the properties of a compound is known as functional group, e.g., -OH (alcohol), -CHO (aldehyde),> C = C < (alkene),- C =C-(alkyne) etc.

7. Homologous series: A series is a series of carbon compounds that have different numbers of carbon atoms but contain the same functional group, e.g., methane, ethane, propane etc. are all part of the alkane homologous series. The general formula of this series is CnHzn+z·

8. Nomenclature
-> Chemists developed a set of rules, for naming organic compounds based on their structures which is known as IUPAC rules.
-> The IUPAC name of an organic compound consists of three parts, i.e.,
prefix – word root- Suffix
-> A word root indicates the nature of basic carbon skeleton.
In case a functional group is present, it is indicated in the name of the compound with either as a prefix or as a suffix.
While adding the suffix to the word root, the terminal ‘e’ of carbon chain is removed.
If the carbon chain is unsaturated then the final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’ respectively for double and triple bonds respectively.

12. Chemical properties of carbon compounds
(i) Combustion: Carbon compound undergo combustion reaction to produce CO2 and H O with the evolution of heat and light.

(ii) Oxidation: It is a process in which a chemical substance changes because of the addition of oxygen. The substances that are used for oxidation are known as oxidising agents, e.g., alkaline KMnO4, and acidified K2Cr2 O7.

(iii) Addition reaction: Unsaturated hydrocarbons (alkenes and alkynes undergo addition reaction in presence of catalysts (such as palladium or nickel) to give saturated hydrocarbons. For e.g.,

(iv) Substitution reaction: Saturated hydrocarbons give substitution reaction. E.g., methane in the presence of sunlight undergoes chlorination

13. Some important carbon compounds:
(i) Alcohols: Compounds containing -OH group attached to a carbon atom are known as alcohols, e.g., ethanol (C2H5OH)
Properties of ethanol
(i) Reaction with sodium: Due to its weak acidic nature, ethanol reacts with sodium to liberate H2 gas.

(ii) Reaction with cone. H2S04: Ethanol can be dehydrated to give ethene by heating with an excess of H2SO4 at about l70°C.

I. Harmful effects of drinking alcohol:
(i) If the alcohol used for drinking purposes contains some methyl alcohol (CH3OH) as impurity then it may cause serious poisoning and loss of eye sight.
(ii) It damages liver if taken regularly in large quantities.

II. Ethanoic acid (acetic acid), CH3COOH: Ethanoic acid, commercially known as acetic acid belongs to a group of acids called carboxylic acid.
Properties of ethanoic acid
(i) Reaction with a base: When an acid, such as acetic acid reacts with a base like NaOH, the products are salt (CH3COONa, sodium acetate)
and water (H2O).

(ii) Reaction with carbonates and bicarbonates: When sodium bicarbonate reacts with acetic acid it forms sodium acetate and water. It also liberates carbon dioxide.
When sodium bicarbonate reacts with acetic acid it forms sodium acetate and water along with carbon dioxide gas.

(iii) Reaction with alcohol (esterification): Ethanoic acid reacts with
ethanol in the presence of cone. H2SO4 as a catalyst to produce the ester, ethyl ethanoate.

(iv) Saponification: Esters react in the presence of an acid or a base to
give back the alcohol and carboxylic acid. This reaction is known as
saponification.

14. Soaps and Detergents: Soaps are sodium or potassium salts of long chain carboxylic acids and detergents are ammonium or sulphurate salts of long chain carboxylic acids.

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