INDEX Syllabus Term-2 Breakdown

7 8

CHEMISTRY 1. Carbon and its Compounds Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

PHYSICS 5. Electricity 9-34 10 18 26 34

ǥȣɐɐ ĔƋĹťčĹĆɐŏêƓƓĹǗĆêƟĹťŚɐ of Elements 35-72 Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

36 47 58 70

ǩȣɐ mêĭŚĔƟĹĆɐ,ǖĔĆƟƓɐťĬɐ Electric Current 169-196 Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

7. Our Environment

3. How do Organisms Reproduce?

73-110

Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

74 83 98 107

Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

134 143 157 167

170 176 189 195

BIOLOGY

BIOLOGY

4. Heredity and Evolution

Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

133-168

111-132 112 117 122 131

Topic Notes Objective Questions Subjective Questions (SA/LA) Topper’s Corner

197-224 198 203 214 222

Syllabus (TERM - 2 Only)

Unit I: Chemical Substances - Nature and Behaviour Chapter 4: Carbon and its 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 and Ethanoic acid (only properties and uses), soaps and detergents.

Chapter 5: Periodic Classification of Elements Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic number, metallic and non-metallic properties.

Unit II: World of Living Chapter 8: How do Organisms Reproduce? Reproduction in animals and plants (asexual and sexual) reproductive health-need and methods of family planning. Safe sex vs HIV/AIDS. Child bearing and women’s health.

Chapter 9: Heredity and Evolution Heredity; Mendel’s contribution- Laws for inheritance of traits: Sex determination: brief introduction; Basic concepts of evolution.

Unit IV: Effects of Current Chapter 12: Electricity Electric current, potential difference and electric current. Ohm’s law; Resistance, Resistivity, Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors and its applications in daily life. Heating effect of electric current and its applications in daily life. Electric power, Interrelation between P, V, I and R.

Chapter 13: Magnetic Effects of Electric Current Magnetic field, field lines, field due to a current carrying conductor, field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming’s Left Hand Rule, Electric Motor, Electromagnetic induction. Induced potential difference, Induced current. Fleming’s Right Hand Rule, Electric Generator, Direct current. Alternating current: frequency of AC. Advantage of AC over DC. Domestic electric circuits. (7)

Unit V: Natural Resources Chapter 15: Our Environment Eco-system, Environmental problems, Ozone depletion, waste production and their solutions. Biodegradable and non-biodegradable substances. Note: Topics marked in Red are removed from the 2021-22 Term-based Syllabus.

PRACTICALS 1. (Unit IV Chapter 12) Studying the dependence of potential difference (V) across a resistor on the current (I) passing through it and determining its resistance. Also plotting a graph between V and I. 2. (Unit II Chapter 8) Studying (a) binary fission in Amoeba, and (b) budding in yeast and Hydra with the help of prepared slides.

TERM-2

BREAKDOWN Units

Units and Chapters

Marks

I

Chemical Substances - Nature and Behaviour

10

II

World of Living

13

III

Effects of Current

12

IV

Natural Resources

05

INTERNAL ASSESSMENT (Periodic Tests (3) + Multiple Assessments (2) + Portfolio (2) + Student Enrichment Activities/ Practical Work (3))

10

TOTAL

40 + 10

These chapters/ topics have been deleted from the Syllabus Units

Chapters Deleted

II

Control and Coordination Sources of Energy

V

Sustainable Management of Natural Resources (Internal Assessment Only)

(8)

1

µzPɐǮ COVALENT BONDING IN CARBON The amount of carbon present in the earth’s crust and in the atmosphere is very less. The earth’s crust has only 0.02% carbon in the form of minerals (like carbonates, hydrogencarbonates,coal and petroleum) and the atmosphere has 0.03% of carbondioxide. Yet, ƿĔɔǚŚčɔƟĴêƟɔêɔŏêƋĭĔɔŚƧŘąĔƋɔťĬɔƟĴĹŚĭƓɔƟĴêƟɔƿĔɔƧƓĔɔĹŚɔ our daily life are made of carbon compounds. Food, clothes, medicines, books and many other things are some examples. The presence of carbon in a material can be tested by burning the substance in air and passing the gas formed through lime water. If the lime water turns milky, then the given material contains carbon. Most carbon compounds are poor conductors of electricity and have low boiling and melting points, from which it can be concluded that the forces of attraction between these molecules are not very strong. Since these compounds are largely non conductors of electricity, we can conclude that the bonding in these compounds does not give rise to any ions. In the case of carbon, it has four electrons in its outermost shell and in order to attain noble gas

ĆťŚǚĭƧƋêƟĹťŚȨɔĹƟɔŚĔĔčƓɔƟťɔĔĹƟĴĔƋɔĭêĹŚɔĬťƧƋɔĔŏĔĆƟƋťŚƓɔťƋɔ lose four electrons. (1) It could gain four electrons forming C4– anion. But as the nucleus contains only six protons, it ƿťƧŏčɔąĔɔčĹǗĆƧŏƟɔĬťƋɔƟĴĔɔŚƧĆŏĔƧƓɔƟťɔĴťŏčɔťŚɔƟťɔƟĔŚɔ electrons. (2) It could lose four electrons forming C4+ cation. But a large amount of energy would be required to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons. Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Apart from carbon, there are many other elements also which form molecules by sharing electrons in this manner. The shared electrons ‘belong’ to the outer shells of both the atoms and lead to both êƟťŘƓɔêƟƟêĹŚĹŚĭɔƟĴĔɔŚťąŏĔɔĭêƓɔĆťŚǚĭƧƋêƟĹťŚȧ Covalent Bond: The types of bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds. Depending upon the number of pairs of electrons shared between atoms, there can be single, double or triple covalent bonds.

Some Examples of Covalent Compounds Compound

Description

Covalent Bonding

Hydrogen (H2) Hydrogen has one electron in its K shell and it requires ťŚĔɔŘťƋĔɔĔŏĔĆƟƋťŚɔƟťɔǚŏŏɔƟĴĔɔaɔƓĴĔŏŏȧɔ¨ťɔƟƿťɔĴDžčƋťĭĔŚɔ atoms share their electrons to form a molecule of hydrogen, H2. × ×

× ×O

× ×

× ×

O O2 molecule

× ×

×× ××

Oxygen atoms

× ×

O

× ×

×

O=O × × ×N ×

×

(N2)

In order to attain an octet, each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons. This is said to constitute a triple bond between the two atoms.

O××

× ×

Nitrogen

A double bond is formed between two oxygen atoms. Each atom of oxygen shares two electrons with another atom of oxygen. The two electrons contributed by each oxygen atom give rise to two shared pairs of electrons. This is said to constitute a double bond between the two atoms.

H H–H

× ×

Oxygen (O2)

× ×

H

× N× × ×

Nitrogen atom

× N ×× ×× N × N2 molecule × × ×× N≡N

Chlorine (Cl2)

Two chlorine atoms share one electron each to form a chlorine molecule thus attaining the nearest inert gas ĆťŚǚĭƧƋêƟĹťŚɔťĬɔ
ƋĭťŚɔȷǩȨɔǯȨɔǯȸȧ

Shared pair of electrons

Cl

Cl

A chlorine molecule, Cl2

10

Science Class X

Water

Two unshared pairs of electrons

Here, one atom of oxygen shares its two electrons with two hydrogen atoms.

(H2O)

or H—O H O H H Water molecule, H2O Cl Cl or Cl — C— Cl Cl C Cl Cl Cl Carbon tetrachloride molecule, CCl4

Hydrogen Chloride

Hydrogen and chlorine atom share one electron each to form a hydrogen chloride molecule.

Shared pair of electrons

— —

(CCl4)

The carbon atom shares its four valence electrons with four chlorine atoms to form carbon tetrachloride molecule.

Carbon Tetrachloride

(HCl) H

Cl

Hydrogen chloride molecule, HCl

Ammonia

Unshared pair of electrons

One atom of nitrogen shares its three valence electrons with three hydrogen atoms and forms ammonia molecule.

(NH3)

—

H N H or H — N — H H H Ammonia molecule NH3

H

×

Methyl chloride Carbon shares its 4 valence electrons with three hydrogen atoms and one chlorine atom (CH Cl)

H× × H C Cl or × × H Electron-dot structure of CH3Cl ×

×

H C Cl

×

3

×

H

Sulphur molecule

A sulphur atom has 6 valence electrons. Eight sulphur atoms combine by sharing two electrons among themselves to form a ring like structure.

(Sǯ)

S S

S S

S S

S S

Example 1. Draw the electron dot structures for (A) Ethanoic acid.

(B) H2S

(C) Propanone.

(D) F2

H

[NCERT]

Ans. (A) Ethanoic acid (CH3COOH):

×

H

×

C

Number of valence electrons of carbon = 4, hydrogen = 1, oxygen = 6

×

Structural formula and electron dot structure is given below:

H

H O | || H — C — C — OH | C

O ×× × ×

C

×

O

H

(B) Hydrogen sulphide (H2S): Number of valence electrons of sulphur = 6, hydrogen = 1 Structural formula and electron dot structure is given:

Carbon and its Compounds

11

H—S—H H . × S . × H

—

— — —

H O H

—

—

H—C—C—C—H H

(C) Propanone (CH3COCH3): Number of valence electrons of carbon = 4, hydrogen = 1, oxygen = 6

H

H

(D) Fluorine (F2):

Structural formula and electron dot structure is given as:

H

O

×

××

× C ×

× C × ×

O

H

H

oƧŘąĔƋɔťĬɔƾêŏĔŚĆĔɔĔŏĔĆƟƋťŚƓɔťĬɔǜƧťƋĹŚĔɔɵɔǮ Structural formula and electron dot structure is given below: F—F

F

F

Properties of Covalent Compounds S.No.

Property

Description

(1)

Covalent compounds are usually This is due to the weak forces of attraction between their liquids or gases molecules.

(2)

Covalent compounds have usually Covalently bonded molecules are seen to have strong bonds low melting and boiling points within the molecule, but intermolecular forces are small

(3)

Usually insoluble in water but This is also due to the presence of strong bonds within the soluble in organic solvents molecule and small intermolecular forces

(4)

Covalent compounds conduct electricity

do

not Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.

$ĹǖĔƋĔŚĆĔƓɐąĔƟƿĔĔŚɐPťŚĹĆɐťŚčɐêŚčɐťƾêŏĔŚƟɐťŚčɐɐ PťŚĹĆɐťŚč

S.No. (1)

An ionic bond is a chemical bond between two In a covalent bond the two atoms come together dissimilar (i.e. a metal and a non-metal) atoms in to share the electron, instead of an atom taking which one atom gives up an electron to another. an electron from another

(2)

An ionic bond is formed between a metal and a A covalent bond is formed between two nonnon-metal. metals that have similar electronegativities.

(3)

mťŏĔĆƧŏĔƓɔĴêƾĔɔŚťɔčĔǚŚĹƟĔɔƓĴêƈĔƓȨɔêƓɔƟĴĔDžɔĴêƾĔɔ mťŏĔĆƧŏĔƓɔĴêƾĔɔêɔčĔǚŚĹƟĔɔƓĴêƈĔȧ lattice structures

(4)

Electrical and thermal conductivity is High

No electrical conductivity conductivity is usually low

(5)

Usually High melting point

Lower melting point

(6)

Usually highly soluble in water

lower solubility

ȷǮȸ

Usually solids at room temperature

Exists as solids, liquids, gases


ŏŏťƟƋťƈĔƓɐťĬɐêƋąťŚ The various physical forms in which an element can exist are called allotropes of the element. Carbon exists in three solid forms called allotropes. The three allotropes of carbon are: (1) Diamond (2) Graphite (3) Fullerenes

12

Covalent Bond

Science Class X

but

Thermal

Diamond (1) Diamonds are colourless, transparent, sparkle êŚčɔƋĔǜĔĆƟɔŏĹĭĴƟȨɔƿĴĹĆĴɔĹƓɔƿĴDžɔƟĴĔDžɔêƋĔɔčĔƓĆƋĹąĔčɔ as lustrous. (2) It is extremely hard and has a high melting point. (3) It does not conduct electricity. Structure of diamond: Diamond is one giant molecule of carbon atoms. Every atom in a diamond is bonded to its neighbours by four strong covalent bonds,

leaving no free electrons and no ions. This explains why diamond does not conduct electricity.

The Structure of Graphite

Uses of graphite: The Structure of Diamond

Uses of diamond:

(1) Powdered graphite is used as a lubricant for the fast moving parts of machinery.

(1) Diamond is used in cutting instruments like glass cutters and in rock drilling equipment, as it is extremely hard.

(2) It is used for making electrodes in dry cells and electric arcs as it is a very good conductor of electricity.

(2) Diamonds are used for making jewellery.

(3) It is used for making core of pencils called ‘pencil leads’.

(3) Sharp-edged diamonds are used by eye-surgeons as a tool to remove cataract.

Graphite (1) Graphite is black, shiny and opaque. (2) It is a very slippery material. (3) Graphite is insoluble in water. (4) It has a high melting point and is a good conductor of electricity, which makes it a suitable material for the electrodes needed in electrolysis.

Fullerenes Fullerenes form another class of carbon allotropes. µĴĔɔ ǚƋƓƟɔ ťŚĔɔ Ɵťɔ ąĔɔ ĹčĔŚƟĹǚĔčɔ ƿêƓɔ Ƚǭǧɔ ƿĴĹĆĴɔ ĴêƓɔ 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.

Structure of graphite : Graphite contains layers of carbon atoms.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, êŚčɔ ƟĴƧƓɔ ƟĴĔɔ ƾêŏĔŚĆDžɔ ťĬɔ ĆêƋąťŚɔ ĹƓɔ ƓêƟĹƓǚĔčȧɔ DƋêƈĴĹƟĔɔ structure is formed by the hexagonal arrays being placed in layers one above the other.

Structure of C-60 Bacminster Fullenene

µzPɐǯ VERSATILE NATURE OF CARBON It is estimated that there are about three million carbon compounds whose formulae are known to chemists which is much greater than the compounds formed by all the other elements put together.

In addition, carbon atoms may be linked by single, double or triple bonds.

The factors due to which this is possible in the case of carbon are:

The atomic number of carbon is 6 and its electronic ĆťŚǚĭƧƋêƟĹťŚɔ ĹƓɔ ǩȨǫȧɔ ĴêƓɔ êɔ ƾêŏĔŚĆDžɔ ťĬɔ ǫȨɔ ĹƟɔ ĆêŚɔ ąťŚčɔ with four other atoms of carbon or atoms of other monovalent element. Carbon forms compounds with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements and these compounds have ƓƈĔĆĹǚĆɔ ƈƋťƈĔƋƟĹĔƓɔ ƿĴĹĆĴɔ čĔƈĔŚčɔ ťŚɔ ƟĴĔɔ ĔŏĔŘĔŚƟƓɔ other than carbon present in the molecule.

Catenation The property of carbon element due to which its atoms can join or link with one another to form long carbon chains is called catenation. These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings.

Tetravalency

Carbon and its Compounds

13

Strong Bonds due to Small Atomic Size The bonds that carbon forms with most other elements are very strong due to its small size making

these bonds very stable. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.

µzPɐǰ HYDROCARBONS

—

—

µĴĔɔǚƋƓƟɔƓƟĔƈɔĹƓɔƟťɔŏĹŚŌɔƟĴĔɔĆêƋąťŚɔêƟťŘƓɔƟťĭĔƟĴĔƋɔƿĹƟĴɔ a single bond and then use the hydrogen atoms to satisfy the remaining valencies of carbon as shown in ǚĭɔąĔŏťƿȧ C—C Step 1 H H Step 2

—

—

H—C—C—H

—

H H Methane: The simplest alkane is methane (CH4). Hydrogen has a valency of 1. As carbon has four valence electrons, carbon shares these electrons with four atoms of hydrogen in order to achieve noble gas ĆťŚǚĭƧƋêƟĹťŚȧ It is widely used as a fuel and is a major component of bio-gas and Compressed Natural Gas (CNG). H H x.

—

x.

14

C

x.

H

x.

H

Science Class X

—

—

—

—

x.

C

x.

x.

H

H

H

(1) The hydrocarbons in which the two carbon atoms are connected by a double bond or a triple bond are called unsaturated hydrocarbons. (2) Unsaturated hydrocarbons may be alkenes (CnH2n) or alkynes (CnH2n-2). (3) The general formula of an alkene is CnH2n, where n is the number of carbon atoms in one molecule. (Ƕ) The general formula of an alkyne is CnH2n-2, where n is the number of carbon atoms in one molecule. (Ƿ) These are more reactive than saturated hydrocarbons due to presence of double and triple bonds which are the sites of chemical reactivity. (Ǹȸɔ µĴĔƓĔɔ ĭĹƾĔɔ êɔ DžĔŏŏťƿɔ ǜêŘĔɔ ƿĹƟĴɔ ŏťƟƓɔ ťĬɔ ąŏêĆŌɔ smoke. This is because the percentage of carbon is comparatively higher than saturated hydrocarbons which does not oxidize completely on combustion.

¨ƟƋƧĆƟƧƋĔɐťĬɐ¼ŚƓêƟƧƋêƟĔčɐKDžčƋťĆêƋąťŚƓ PŚɔ ƟĴĔɔ ǚƋƓƟɔ ƓƟĔƈȨɔ Ɵƿťɔ ĆêƋąťŚɔ êƟťŘƓɔ ŏĹŚŌɔ ƟťĭĔƟĴĔƋɔ ąDžɔ single bond. Each carbon atom combines with two hydrogen atoms. One valency per carbon atom ƋĔŘêĹŚƓɔƧŚƓêƟĹƓǚĔčɔƿĴĹĆĴɔĆêŚɔąĔɔƓêƟĹƓǚĔčɔťŚŏDžɔĹĬɔƟĴĔƋĔɔ is a double bond between the two carbon atoms. ,ƟĴĔŚĔɐȥɐµĴĔɐƓĹŘƈŏĔƓƟɐêŏŌĔŚĔȥ Ethene is the simplest alkene having two carbon atoms and its molecular formula is C2H4. There is a double bond between the two carbon atoms and four single bonds between carbon and hydrogen atoms. H

H .x H .x

H C —C

—

H

H

x

x.

¼ŚƓêƟƧƋêƟĔčɐ KDžčƋťĆêƋąťŚƓɐ ȳ
ŏŌĔŚĔƓɐ êŚčɐ
ŏŌDžŚĔƓȴɐ

—

H—C—H

H H

C

H

—

¨ƟƋƧĆƟƧƋĔɐťĬɐ¨êƟƧƋêƟĔčɐKDžčƋťĆêƋąťŚƓ

H—C—C—H H

—

The hydrocarbons in which the carbon atoms are connected by only single bonds are called saturated hydrocarbons or alkanes. ȷdzȸ The general formula of saturated hydrocarbons are alkanes is CnH2n+2, where n is the number ťĬɔ ĆêƋąťŚɔ êƟťŘƓɔ ĹŚɔ ťŚĔɔ ŘťŏĔĆƧŏĔȧɔ µĴĔɔ ǚƋƓƟɔ ĬĔƿɔ alkanes are methane (CH4), ethane (C2H6) and propane (C3Hǯ). ȷǴȸ The saturated hydrocarbons are not very reactive. ȷǵȸ The saturated hydrocarbons generally give a ĆŏĔêŚɔ ǜêŘĔȧɔ µĴĹƓɔ ĹƓɔ ąĔĆêƧƓĔɔ ƟĴĔɔ ƈĔƋĆĔŚƟêĭĔɔ ťĬɔ carbon is comparatively low which gets oxidized completely on combustion.

H.

x

H

C

xx xx

H

C

x.

H

ȷDzȸ

H.

H H

.x

¨êƟƧƋêƟĔčɐKDžčƋťĆêƋąťŚƓɐťƋɐ
ŏŌêŚĔƓ

Ethane: Ethane is an alkane having two carbon atoms. The molecular formula of ethane is C2H6. There are seven single covalent bonds present in one molecule of ethane – one covalent bond between the two carbon atoms and six single bonds between carbon and hydrogen atoms.

x.

The compounds made up of hydrogen and carbon only are called hydrocarbons. These are the simplest organic compounds and all other compounds are considered to be derived from them by the replacement of one or more hydrogen atoms by other atoms or groups of atoms. The most important natural source of hydrocarbons is petroleum. There are two types of hydrocarbons: ȷDzȸ Saturated hydrocarbons ȷdzȸ Unsaturated hydrocarbons

,ƟĴDžŚĔȻµĴĔɐ ƓĹŘƈŏĔƓƟɐ êŏŌDžŚĔȥɐ The simplest alkyne is ethyne having two carbon atoms and its molecular formula is C2H2. There is a triple bond between the two carbon atoms and two single bonds between carbon and hydrogen atoms. xx xx xx

C

C

H

H

H

H

H

C

C x.

H

C

H

C H

H

Chains, Branches and Rings

H

—

—

—

—

—

—

—

—

—

—

—

—

—C—C—C—C—C—C— —C—C—C—C—C—C— —C—

—

(a) Straight chain of carbon atoms

¨ƟƋƧĆƟƧƋêŏɐPƓťŘĔƋĹƓŘ Organic compounds having the same molecular ĬťƋŘƧŏêɔąƧƟɔčĹǖĔƋĔŚƟɔƈĴDžƓĹĆêŏɔêŚčɔĆĴĔŘĹĆêŏɔƈƋťƈĔƋƟĹĔƓɔ čƧĔɔƟťɔčĹǖĔƋĔŚƟɔƓƟƋƧĆƟƧƋĔƓɔêƋĔɔĆêŏŏĔčɔƓƟƋƧĆƟƧƋêŏɔĹƓťŘĔƋƓɔ and this property is called isomerism. Isomerism is possible only with hydrocarbons having 4 or more carbon atoms. If we look at the structure of butane (C4H10ȸȨɔƿĔɔǚŚčɔ ƟĴêƟɔ Ɵƿťɔ čĹǖĔƋĔŚƟɔ ɉƓŌĔŏĔƟťŚƓɊɔ êƋĔɔ ƈťƓƓĹąŏĔɔ ƿĹƟĴɔ ĬťƧƋɔ carbon atoms having single covalent bond:

(b) Branched chain of carbon atoms

C—C—C—C—

C—C

C

—

—

—

—

—

H

—

— H

—

H H H H

—

H—C— C

—

H—C—C—C—C—H

C

H H H

H H ÔĔɔ ǚŚčɔ ƟĴêƟɔ ąťƟĴɔ ƟĴĔƓĔɔ ĆťŘƈťƧŚčƓɔ ĴêƾĔɔ ƟĴĔɔ ƓêŘĔɔ molecular formula C4H10ɔąƧƟɔčĹǖĔƋĔŚƟɔƓƟƋƧĆƟƧƋĔƓɔêŚčɔ hence they called Give isomers. PƓťŘĔƋƓɐťĬɐĴĔDŽêŚĔȥ

—

—

—

—

—

H H H H H H

—

Some compounds have carbon atoms arrangedin the form of a ring as in the case of cyclohexane (C6H12). Its structure is shown below. Similarly, the structure of benzene (C6H6) is also shown alongside:

C H

H H H H

(c) Closed chain of carbon atoms

C

—

—

—

—

—

—

—

—

—

—

—

—

—

Carbon atoms can form long ‘chains’ containing tens of carbon atoms. When carbon atoms combine, three types of chains can be formed: ȷDzȸɔɔStraight chains ȷdzȸɔɔBranched chains ȷǴȸɔɔClosed chains or ring type chains.

—

.x C

H—C {C—H

Electron dot structure:

H H H

HH

H

C —— C H H

C

—

—

—

—

H H H H H H

H

C —— C C

—

—

(1) H—C—C—C—C—C—C—H

H

(2)

H

H

(a) (3) Benzen —C6H6

C H H H H

H H CH3 H

—

—

—

—

—

(5) H—C—C—C—C—H —

—

—

(4) H—C—C—C—C—H

H H H H

—

—

—

—

—

H H CH3 H

—

Ans. The formula of cyclopentane is C5H10 and its electron dot structure is given below: Structural formula: H H

—

Example 2. ÔĴêƟɐƿĹŏŏɐąĔɐƟĴĔɐĬťƋŘƧŏêɐêŚčɐĔŏĔĆƟƋťŚɐ dot structure of cyclopentane? [NCERT]

H CH3 H CH3

Example 3. How many structural isomers can you

C

C

C

C

H H H H

draw for pentane? [NCERT] Ans. The molecular formula for pentane is C5H12. There are three structural isomers of pentane as given below:

Carbon and its Compounds

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