‘रचना-प्रयोग’ का मुख्य उद्देश्य क्या है?

व्याकरण का व्यावहारिक प्रयोग सिखाना

‘द्वितीयः’ किस प्रकार की संख्या है?

क्रमवाचक (दूसरा)

Why does carbon form mostly covalent compounds?

With four valence electrons it can neither easily lose nor gain four electrons, so it shares them, forming covalent bonds.

What is the role of a micelle in cleaning?

The soap’s tails dissolve in oily dirt while the heads face water, lifting the dirt away as a suspended micelle.

Why does carbon form a very large number of compounds?

Because of catenation (its ability to bond with other carbon atoms forming long chains, branches and rings) and tetravalency (its capacity to form four covalent bonds).

What is a covalent bond, and why do carbon compounds have low melting points?

A bond formed by the sharing of electron pairs; carbon compounds are usually molecular with weak inter-molecular forces, so they melt and boil at low temperatures and conduct electricity poorly.

Distinguish between saturated and unsaturated hydrocarbons.

Saturated hydrocarbons (alkanes) have only single bonds between carbon atoms; unsaturated hydrocarbons (alkenes, alkynes) have at least one double or triple bond.

What is a functional group? Give two examples.

An atom or group of atoms that gives a compound its characteristic properties, e.g. the –OH (alcohol) group and the –COOH (carboxylic acid) group.

What is a homologous series?

A family of organic compounds with the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit.

Describe two important reactions of ethanol.

Ethanol burns in air (combustion) giving CO₂, water and heat, and on heating with excess concentrated sulphuric acid it undergoes dehydration to form ethene.

Why is ethanoic acid called glacial acetic acid, and how does it react with a base?

Pure ethanoic acid freezes in cold climates to an ice-like solid, hence "glacial"; with a base such as NaOH it gives sodium ethanoate (a salt) and water.

How do soaps clean, and why do they not work well in hard water?

Soap molecules form micelles that trap oily dirt with their tails while the heads stay in water, washing the dirt away; in hard water they react with calcium/magnesium ions to form scum, so detergents are used instead.

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Chapter 4: Carbon and its CompoundsClass 10 Science — summary, notes, extra questions & NCERT solutions

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The valency of carbon is:

Summary

Carbon forms a vast number of compounds because of two properties: catenation, its ability to bond with other carbon atoms in long chains, branches and rings, and tetravalency, its capacity to form four covalent bonds. Covalent bonding by sharing electrons gives molecules with low melting points and poor conductivity. Hydrocarbons may be saturated (alkanes, single bonds) or unsaturated (alkenes and alkynes, with double or triple bonds). Functional groups such as alcohols, aldehydes, carboxylic acids and ketones give families of compounds their characteristic chemistry, and a homologous series is a group of such compounds differing by a –CH₂– unit. The chapter examines ethanol and ethanoic acid in detail, along with important reactions like combustion, oxidation, addition and substitution, and explains the cleansing action of soaps and detergents through micelle formation.

Covalent bonding in carbonCatenation and tetravalencyHydrocarbons and functional groupsEthanol and ethanoic acidSoaps and detergents

Key terms

Catenation

Self-linking of carbon atoms into chains and rings.

Covalent bond

A bond formed by sharing electron pairs between atoms.

Homologous series

Compounds with the same functional group differing by –CH₂–.

Micelle

A cluster of soap molecules that traps oily dirt in water.

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Self-linking of carbon atoms into chains and rings.

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Chapter 4: Carbon and its CompoundsClass 10 Science — summary, notes, extra questions & NCERT solutions

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