NCERT Solutions for Class 10 science Chapter 4: Carbon and Its Compounds

Structural isomers for bromopentane: There are three structural isomers for bromopentane depending on the position of Br at carbon 1, 2, 3.

Positions 4 and 5 are same as 1, 2.

In CH₃Cl : C = 6, H = 1 and Cl = 17 And their electronic configuration is C – 2,4, H – 1 and Cl – 2, 8, 7

Three hydrogen atoms complete their shells by sharing three electrons (one electron each) of carbon atom.
Chlorine completes its outer shell by sharing its one out of seven electrons with one electron of carbon atom.
Thus carbon atom shares all its four electrons with three hydrogen atoms and one of chlorine atom and completes its outermost shell and single covalent bonds are formed in CH₃Cl.

Characteristics of homologous series :
(i) All members of a homologous series can be represented by the same general formula. For example, the general formula of the homologous series of alkanes is C_nH_2n+2, in which ‘n’ denotes number of carbon and hydrogen atoms in one molecule of alkane.
(ii) Any two adjacent homologues differ by one carbon atom and two hydrogen atoms in their molecular formulae.
(iii) The difference in the molecular masses of any two adjacent homologues is 14u.
(iv) All the compounds of a homologous series show similar chemical properties.
(v) The members of a homologous series show a gradual change in their physical properties with increase in molecular mass.

For example, general formula of the homologous series of alkanes is C_nH_2n+2, in which ‘n’ denotes number of carbon atoms in one molecule of alkane. Following are the first five members of the homologous series of alkanes (general formula C_nH_2n+2).

Difference on the basis of chemical properties

• Cooking oil decolourises bromine water showing that it is an unsaturated compound.
• Butter does not decolourise bromine water showing that it is a saturated compound.

Carbon compounds: Covalent bonding in carbon compounds, Versatile nature of carbon, Homologous series, Nomenclature of carbon compounds containing functional groups, (halogens, alcohol, ketones, aldehydes, alkanes, and alkynes), difference between saturated hydrocarbons and unsaturated hydrocarbons. Chemical properties of carbon compounds (combustion, oxidation, addition and substitution reaction). Ethanol (only properties and uses), Ethanoic acid (only properties and uses), soaps and detergents.

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Multiple Choice Questions (MCQs) [1 Mark each]

₄= 2, 8.
Atomic number of Ne is 10. Its electronic K L configuration is 2,8. Therefore, after the formation of four bonds, carbon attains the electronic configuration of neon.

Which structure do the ester compounds in the table have in common?

Answer:
(d) All esters have the common structure of carboxylic group represented by the suffix date.

Class 10 Science Carbon and its Compounds Mind Map

Carbon is an important constituent of the foods, fuels, household and commercial articles, textile fabrics, perfumes, explosives, dyes, war gases etc. The Earth’s crust has only 0.02% carbon in the form of minerals (like petroleum, coal, carbonates and hydrogen carbonates) and the atmosphere comprises of only 0.03% of carbon dioxide

Allotropes of Carbon
An element, in different forms, having different physical properties but similar chemical properties is known as allotropes of that element.
Carbon has three well known allotropes which are graphite, diamond and buck minster fullerene.
Graphite:

• In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array.
• One of these bonds is a double-bond, and thus the valency of carbon is satisfied.
• Graphite structure is formed by the hexagonal arrays being placed in layers one above the other.
• Unlike other non-metals graphite is a very good conductor of electricity.

Diamond:

• In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure.
• Diamond is the hardest substance known while graphite is smooth and slippery.
• Diamonds can be synthesized by subjecting pure carbon to very high pressure and temperature.
• These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.

Fullerene:
This is 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. Since this looked like the geodesic dome designed by the US architect Buckminster Fuller, the molecule was named fullerene.

Saturated and Unsaturated Hydrocarbons
Saturated hydrocarbons:Compounds in which carbon- carbon atoms & carbon-hydrogen atoms are held together by single bonds. General formula is C_nH_2n+2.
Unsaturated hydrocarbons:Compounds consist of a single, double or triple bond between carbon-carbon atoms.
These double-bonded compounds are called alkenes & the triple-bonded compounds are called alkynes.
The general formula for alkenes is C_nH_2n& for alkynes the same is C_nH_2n-2.
Cycloalkanes:These hydrocarbons possess one or multiple carbon rings. The hydrogen atom is attached to the carbon ring.
Aromatic hydrocarbons:These are also called as arenes. Arenes are compounds which consist of at least one aromatic ring.

Bonding in Carbon

• Atomic number of carbon = 6
• Electronic configuration has 2 electrons in KL shell and 4 electrons in L shell.
• Carbon shares its four valence electrons with other atoms of carbon or with atoms of other elements. These electrons contributed by the atoms, for mutual sharing in order to acquire the stable noble gas configuration is called covalencv of that atom.
• Hence, carbon shows tetracovalency.
• The simplest molecule formed by sharing of electrons (i.e., covalent bonds), can be represented by electron dot structure.

Versatile Nature of Carbon

• Catenation:It is the unique property of self linkage of carbon atoms by means of covalent bonds to form straight chains, or branched chains, or the rings of different sizes.
• Tetracovalency:Due to small size, and presence of four valence electrons, carbon can fonn strong bonds with other carbon atoms, hydrogen, oxygen, nitrogen, or sulphur, etc. For example, compounds of carbon with hydrogen are called hydrocarbons.
• Multiple Bond Formation:Due to small size, it forms multiple bonds (i.e., double bonds or triple bonds) with other elements as well as with its own atoms.
• Isomerism:The phenomenon by means of which the carbon compounds with same molecular formula show different structures, and properties.

Soaps:Ester of higher fatty acids is called soap. It is manufactured by the reaction of caster of higher fatty acid with sodium hydroxide. The sodium salt so formed has cleansing property.
Detergents:Soap cannot form lather in hard water. To overcome this problem, detergents were introduced. Detergent is also known as soapless soap. Detergent is sodium salt of benzene sulphonic acid or sodium salt of long chain alkyl hydrogen sulphate.

Nomenclature of Carbon Compounds: IUPAC Name
Rales for Nomenclature of Organic Compounds:

• Identify the number of carbon atoms in the compound & name the compound according to the number of carbon atoms.
• If any functional group is present, add a ‘prefix’ or ‘suffix’ specified for the functional group with the name of the parent compound.
• Prefix is added for only Halo group and for rest of the functional groups suffix is added.
• If the name of the functional group is to be given as a suffix, the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix.
• In the case of unsaturated hydrocarbon if double bond is present in the carbon chain, then ‘ene’ will be added in the parent name of compound after omitting ‘ane’ and if triple bond is present in the carbon chain, then ‘yne’ will be added.

Properties of Ethanol

• Ethanol exists in liquid state at room temperature.Mixture of alcohol to ethane results in the fonnation of ethanol & it is the active ingredient of all alcoholic drinks. Even a small quantity of ethanol if consumed can causes drunkenness.Being a good solvent, it is also used in medicines like tincture of iodine, cough syrups, and many other tonics.Reaction with sodium –
  

Properties of Ethanoic Acid

• Ethanoic acid commonly known as acetic acid belongs to a group of carboxylic acids.Vinegar used in our day to day life is a 5-8% solution of acetic acid in water. It is extensively used as a preservative in pickles.Pure ethanoic acid has a melting point of290 K due to which it
  often freezes in cold climates giving rise to its name as glacial acetic acid.
  
• Reaction with a base: NaOH + CH₃COOH → CH₃COONa + H₂O
• Reaction with carbonates and hydrogen carbonates:
  2CH₃COOH + NA₂CO₃→ 2CH₃COONa + H₂O + CO₂
  CH₃COOH + NaHCO₃→ CH₃COONa + H₂O + CO₂

Homologous Series

• A series of carbon compounds in which same functional group substitutes the hydrogen atom is called a homologous series.
• These compounds have similar chemical properties due to the presence of same kind of functional group. For e.g. series of alkanes i.e. methane, ethane, propane, butane and so on is a homologous series.
• Similarly the series of alkene & alkynes also forms homologous series.
• The series like methanol, ethanol, propanol, butanol and so on is also a homologous series. The functional group attached to these compounds is alcohol.
• With the increase in molecular mass in a homologous series the physical properties like melting points, boiling points & solubility in a particular solvent increases.
• But the chemical properties of a homologous series determined by the functional group remain same.

Chemical Properties of Carbon Compounds
Combustion Reactions:When Carbon & its compounds bum in the presence of Oxygen (or air), they give CO₂, heat & light.
E.g.: C + O₂→ CO₂+ Heat + Light.
Oxidation Reactions:Though combustion is generally an oxidation reaction, not all oxidation reactions are combustion reactions. Oxidation is also carried out by using oxidizing agents (Oxidants).
Addition reactions:Unsaturated organic compounds, like alkenes and alkynes, undergo addition reactions to become saturated in nature.
E.g. CH₂= CH₂+ H₂+ (Nickel catalyst) → CH₃– CH₃
Substitution Reaction:A Substitution reaction is one in which an atom or a group of atoms (functional group) in the compound are replaced by another atom ( or group of atoms). Substitution reactions are single displacement reactions.
E.g.: CH₄+ Cl₂+ Sunlight → CH₃Cl + HCl

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