Chapter 4 Carbon and its Compounds Notes

1. Bonding in Carbon 

Carbon form covalent bonds. 

Formation of covalent bond : 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 ofthe chemical properties is known as “Allotropy” and the various forms are  called “Allotropes”. 

∙ Carbon exists in two allotropic form (i) crystalline (ii) 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. Unique Nature of Carbon 

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 the 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.

5. Straight chain compounds : The compounds which contain straight chain of carbon  atoms e.g. normal butane (C₄H₁₀), normal pentane (₅H₁₂) etc. 

6. Branched chain compounds : Those compounds which are branched. e.g. iso-butane (C₄H₁₀), isopentane (C₅H₁₂), neopentane (C₅H₁₂) etc. 

7. Closed chain compounds or Ring compounds : 

Cyclic compounds are called closed chain or ring compounds e.g. cyclohexane  (C₆H₁₂), cyclopentane (C₅H₁₀), cyclobutane (C₄H₈), cyclopropane (C₃H₆) etc. 

8. Hydrocarbons 

All those compounds which contain just carbon and hydrogen are called hydrocarbons. 9. 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. 

10. Homologous Series 

A series of compounds in which the same functional group substitutes hydrogen in a carbon  chain is called a homologous series. 

e.g. CH₃C₁ and C₂H₅C₁ differ by a —CH₂ unit. 

11. 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 compounds consists of three parts. 

Prefix – word root – Suffix 

Word Root : 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 „en& or yne‟ respectively for double and triple bonds.

12. Chemical Properties of Carbon Compounds : 

(i) Combustion : Carbon compound undergo combustion reaction to produce CO₂ and H₂0  with the evolution of heat and light. 

CH₄ +O₂ > CO₂ + ₂O + heat and light 

(ii) Oxidation : 

The substance which are used for oxidation are known as oxidising agent. 

e.g alkaline KMnO₄, acidified K₂Cr₂O₇. 

(iii) Addition reaction : 

Unsaturated hydrocarbons (alkenes and alkynes undergo addition reaction in presence of  catalysts e.g.

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(iv) Substitution reaction : Saturated hydrocarbons give substitution reaction e.g. methane in  presence of sunlight undergo chlorination. 

13. Some Important Carbon Compounds 

Alcohols : Compounds containing -OH group attached to a carbon atom are known as alcohols. Example : Ethanol (C₂H₅OH) : commonly known as alcohol. 

Properties of ethanol : 

1. Reaction with sodium : Due to its weakly acidic nature, ethanol reacts with sodium to  librate H₂ gas. 

2. Reaction with conc : H₂SO₄ : 

Alcohol as a fuel : Alcohol (ethanol) is added to petrol upto 20% and the mixture is called  “gasol”. 

Harmful Effects of Drinking Alcohol : 

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. 

It is habit forming and damages liver if taken regularly in large quantities. Ethanoic Acid (Acetic Acid) CH₃COOH: 

Ethanoic acid, commercially known as acetic acid belongs to a group of acids called carboxylic  acid. 

Chemical properties : 

(i) Reaction with a base : 

2CH₃COOH + 2NaOH → 2CH₃COONaH₂O 

(ii) Reaction with carbonates and bicarbonates : 

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O

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CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂ 

(iii) Reaction with alcohol : (Esterification) 

Esters react is 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 : Soaps are sodium or potassium salts of long chain acid carboxylic acids. Detergent : They are ammonium or sulphurate salts of long chain carboxylic acids.