1 -Atomic Structure

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1. 1. ATOMIC STRUCTU

ATOMIC STRUCTURE

RE

INTRODUCTION:

All objects around us, this book, your pen, and other things of nature such as rocks, water plants All objects around us, this book, your pen, and other things of nature such as rocks, water plants and animal substances – constitute the matter of the universe. Matter can be classified into pure and animal substances – constitute the matter of the universe. Matter can be classified into pure substances and mixtures.

substances and mixtures. A pure A pure substance is a single, uncontaminated substance. A mixture is substance is a single, uncontaminated substance. A mixture is a physicala physical combination of two or more pure substances. There are two types of pure substances known as

combination of two or more pure substances. There are two types of pure substances known as elementselements and compounds

and compounds..

Elements are fundamental substances, which cannot be fragmented into simpler fundamental substances. Elements are fundamental substances, which cannot be fragmented into simpler fundamental substances. Compounds are composed of elements and they can be separated into its constituent elements. The British Compounds are composed of elements and they can be separated into its constituent elements. The British chemist John Dalton (1766-1844) provided the basic theory that

chemist John Dalton (1766-1844) provided the basic theory that all matter isall matter is composed of composed of small particlessmall particles called atoms

called atoms..

In 1897, the British physicist J.J. Thomson discovered the first component part of the atom In 1897, the British physicist J.J. Thomson discovered the first component part of the atom thethe electron

electron and in 1904 he proposed and initial model of an atom. In 1911, Rutherford put forward the idea and in 1904 he proposed and initial model of an atom. In 1911, Rutherford put forward the idea of the nuclear model of the atom, based on experiments done in his laboratory. But he could not explain of the nuclear model of the atom, based on experiments done in his laboratory. But he could not explain the stability of atom. In order to take account of atomic stability, in 1913 Niels Bohr, created a new model the stability of atom. In order to take account of atomic stability, in 1913 Niels Bohr, created a new model of atom.

of atom.

Until 1923, all attempts to deal with atomic and molecular structural problems were based on Until 1923, all attempts to deal with atomic and molecular structural problems were based on

classical mechanics

classical mechanics , , in which structural units of the atom were treated asin which structural units of the atom were treated as particles. particles. The modern theory of The modern theory of atomic structure is based o the

atomic structure is based o the quantumquantum or wave or wave mechanicsmechanics proposed independently by de Broglie, proposed independently by de Broglie, Heisenberg and Schrodinger.

Heisenberg and Schrodinger.

IMPORTANT TERMS, DEFINITIONS AND FORMULAE IMPORTANT TERMS, DEFINITIONS AND FORMULAE ATOM:

ATOM: An atom is the smallest particle of matter consisting of a positively charged nucleus andAn atom is the smallest particle of matter consisting of a positively charged nucleus and negatively charged electrons.

negatively charged electrons.

DALTON’S ATOMIC MODEL:

DALTON’S ATOMIC MODEL:This model suggest that atoms are indivisible.This model suggest that atoms are indivisible.

J.J. THOMSON’S MODEL:

J.J. THOMSON’S MODEL:An atom is a solid sphere of positively charged particles in which electronsAn atom is a solid sphere of positively charged particles in which electrons are embedded like seeds in watermelon fruit.

are embedded like seeds in watermelon fruit.

RUTHERFORD’S MODEL.

RUTHERFORD’S MODEL. The protons and neutrons are present in a small dense positively chargedThe protons and neutrons are present in a small dense positively charged core called nucleus and all the electrons revolve around the nucleus in circular paths like planetary model. core called nucleus and all the electrons revolve around the nucleus in circular paths like planetary model.

BOHR’S MODEL.

BOHR’S MODEL. The protons and neutrons are present in the nucleus and all the electrons revolveThe protons and neutrons are present in the nucleus and all the electrons revolve around the nucleus in definite orbits.

around the nucleus in definite orbits.

SOMMERFIELD MODEL:

SOMMERFIELD MODEL: According to this, the electron moving around the nucleus must describe anAccording to this, the electron moving around the nucleus must describe an elliptical orbit in addition to circular orbits as suggested by Bohr.

elliptical orbit in addition to circular orbits as suggested by Bohr.

QUANTUM MECHANICAL MODEL OF AN ATOM:

QUANTUM MECHANICAL MODEL OF AN ATOM: According to this, electrons are considered asAccording to this, electrons are considered as

three dimensional wave

three dimensional wave in electric field of the positively charged nucleus. in electric field of the positively charged nucleus.

ELECTRON:

ELECTRON: It is a negatively charged particle which occupies the space outside the nucleus in an atom. It is a negatively charged particle which occupies the space outside the nucleus in an atom.

PROTON:

PROTON: It is a positively charged particles present in the nucleus of an atom. It is a positively charged particles present in the nucleus of an atom.

NEUTRON:

NEUTRON: It is a neutral particle of mass equal to the mass of proton. It is a neutral particle of mass equal to the mass of proton.

ORBIT:

ORBIT: It is a definite circular path in which the electron is supposed to revolve around the nucleus. It is a definite circular path in which the electron is supposed to revolve around the nucleus.

ORBITAL:

ORBITAL: It is the three dimensional region around the nucleus in which the probability of finding theIt is the three dimensional region around the nucleus in which the probability of finding the electron is maximum.

electron is maximum.

ELECTRONIC CONFIGURATION:

ELECTRONIC CONFIGURATION: Distribution of electron in different orbitals of the atom of anDistribution of electron in different orbitals of the atom of an element.

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s-ORBITAL:

s-ORBITAL: s orbital is spherically symmetric around the nucleus.s orbital is spherically symmetric around the nucleus.

p-OTBITAL:

p-OTBITAL: p orbital is dumb-bell shaped and consists of two lobes of electron cloud.p orbital is dumb-bell shaped and consists of two lobes of electron cloud.

PRINCIPAL QUANTUM NUMBER (

PRINCIPAL QUANTUM NUMBER ( n n):): It describes the energy of the energy level in which theIt describes the energy of the energy level in which the electron revolving around the nucleus. It also describes the distance between the nucleus and the electron. electron revolving around the nucleus. It also describes the distance between the nucleus and the electron.

AZIMUTHAL OR ORBITAL QUANTUM NUMBER (

AZIMUTHAL OR ORBITAL QUANTUM NUMBER (l l ):): It represents the sub energy level which isIt represents the sub energy level which is present in main energy level.

present in main energy level.

MAGNETIC QUANTUM NUMBER (

MAGNETIC QUANTUM NUMBER ( m) m):: It gives how many orientations are possible for a sub energy It gives how many orientations are possible for a sub energy level in space, when an electron present in a sub shell.

level in space, when an electron present in a sub shell.

SPIN QUANTUM NUMBER (

SPIN QUANTUM NUMBER ( s s):): It describes the direction of the spin of the electron (either clock wise It describes the direction of the spin of the electron (either clock wise or anticlock wise).

or anticlock wise).

HUND’S RULE:

HUND’S RULE: ““Among the orbitals of same energy, electrons do not start pairing, until all these orbitalsAmong the orbitals of same energy, electrons do not start pairing, until all these orbitals are singly occupied”. Hund’s rule is also called as the principle of minimum pairing and the principle of are singly occupied”. Hund’s rule is also called as the principle of minimum pairing and the principle of maximum multiplicity.

maximum multiplicity.

AUFBAU’S PRINCIPLE:

AUFBAU’S PRINCIPLE: “Electrons are filled in the increasing order of energy level” According to this“Electrons are filled in the increasing order of energy level” According to this principle first the electrons occupy the orbitals with lowest energy. This is decided by the sum of the principle first the electrons occupy the orbitals with lowest energy. This is decided by the sum of the principle quantum number and azimuthal quantum number. This is called (

principle quantum number and azimuthal quantum number. This is called (nn + +ll) rule.) rule.

PAULI PRINCIPLE:

PAULI PRINCIPLE: “In an atom no two electrons can have the same set of four quantum numbers”.“In an atom no two electrons can have the same set of four quantum numbers”.

OXIDATION:

OXIDATION: Removal of one or more electron from an atom or molecule or ion is called oxidation Removal of one or more electron from an atom or molecule or ion is called oxidation

REDUCTION:

REDUCTION:Addition of one or more electrons to an atom or molecule or ion is called reduction.Addition of one or more electrons to an atom or molecule or ion is called reduction.

REDUCING AGENT:

REDUCING AGENT: A substance which gives one or more electrons to the other is called a reducingA substance which gives one or more electrons to the other is called a reducing agent.

agent.

OXIDISING AGENT:

OXIDISING AGENT: A substance which accepts one or more electrons from the other is called anA substance which accepts one or more electrons from the other is called an oxidizing agent.

oxidizing agent.

SELF EVALUATION (T.B. PAGE 19 & SELF EVALUATION (T.B. PAGE 19 & 20)20) I. CHOOSE THE CORRECT ANSWER:

I. CHOOSE THE CORRECT ANSWER:

1. What would be the

1. What would be the 11 value for an electron having n value 2? value for an electron having n value 2? a)

a) 1 1 b) b) 2 2 c) c) 2, 2, 0 0 d) d) 0, 0, 11 2. The quantum number which gives the orientation of a given electron is 2. The quantum number which gives the orientation of a given electron is

a)

a) Principal Principal quantum quantum number number b) b) Magnetic Magnetic quantum quantum numbernumber c)

c) Azimuthal Azimuthal quantum quantum number number d) d) Spin Spin quantum quantum numbernumber 3.In an atom no two electrons have the same set of four quantum numbers. It is 3.In an atom no two electrons have the same set of four quantum numbers. It is

a)

a) Pauli’s Pauli’s exclusion exclusion principlprinciple e b) b) Hund’s Hund’s rule rule c) c) Aufbau Aufbau principle principle d) d) Bohr’s Bohr’s principlprinciplee 4.The ground state electronic configuration of carbon is

4.The ground state electronic configuration of carbon is a) 1s

a) 1s22 2s 2s22 2p 2pxx11 2p 2pyy11 2p 2pzz00 b) 1 b) 1 ss22 2s 2s112p2pxx11 2p 2pyy11 2p 2pzz11

c) 1s

c) 1s22 2s 2s22 2p 2pxx22 2p 2pyy00 2p 2pzz00 d) 1sd) 1s11 2s 2s22 2p 2pxx11 2p 2pyy11 2p 2pzz11

5.The oxidation number of manganese in KMnO 5.The oxidation number of manganese in KMnO44 is is

a)

a) +2 +2 b) b) –2 –2 c) c) +1 +1 d) d) +7+7

6. The direction of the spin of electron is explained by …………quantum number. 6. The direction of the spin of electron is explained by …………quantum number.

a)

a) Principal Principal b) b) AzumithAzumithal al c) c) magnemagnetic tic d) d) SpinSpin 7. The q

7. The quantuuantum m number which gives the maximum number of enumber which gives the maximum number of electrolectrons in ns in a shell is………. a shell is………. quantum numberquantum number a)

a) Principal Principal b) b) AzumithAzumithal al c) c) Magnetic Magnetic d) d) SpinSpin 8. The electron will enter subshell for which (n +

8. The electron will enter subshell for which (n + ll) value is………..) value is……….. a)

a) Lowest Lowest b) b) Highest Highest c) c) both both (a) (a) & & (b) (b) d) d) NoneNone 9. Oxidation number of hydrogen in LiH is………….

9. Oxidation number of hydrogen in LiH is…………. a)

a) +1 +1 b) b) –1 –1 c) c) +2 +2 d) d) –2–2 10.A substance which accepts one or

10.A substance which accepts one or more more electrons from the other is electrons from the other is called …………called ………… a)

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__________________________________________________________________________________ __________________________________________________________________________________ Answers:

Answers: 1.

1. (d) (d) 2. 2. (b) (b) 3. 3. (a) (a) 4. 4. (a) (a) 5. 5. (d) (d) 6. 6. (d) (d) 7. 7. (a) (a) 8. 8. (a) (a) 9. 9. (b) (b) 10. 10. (a).(a).

_____________________________________________________________________________________ _____________________________________________________________________________________ II. ANSWER THE FOLLOWING IN ONE OR TWO SENTENCES: (T.B PAGE 21)

II. ANSWER THE FOLLOWING IN ONE OR TWO SENTENCES: (T.B PAGE 21)

1.State Hund’s rule. 1.State Hund’s rule.

“Among the orbitals of same energy, electrons do not start pairing, until all these orbitals are singly “Among the orbitals of same energy, electrons do not start pairing, until all these orbitals are singly occupied”.

occupied”.

Hund’s rule is also called as the principle of minimum pairing and the principle of maximum multiplicity. Hund’s rule is also called as the principle of minimum pairing and the principle of maximum multiplicity. 2.Define oxidation and reduction in terms of electron transfer.

2.Define oxidation and reduction in terms of electron transfer. Removal of one or more electrons from a particle is called

Removal of one or more electrons from a particle is called oxidationoxidation. Addition of one or more electrons to a. Addition of one or more electrons to a particle is called

particle is called reductionreduction.. Example, Example, 1. 1. Na Na NaNa++ + e + e-- (oxidation) (oxidation) 2. 2. Cl Cl + + ee-- ClCl-- (Reduction) (Reduction) 3. Draw the shape of

3. Draw the shape of p p-orbitals.-orbitals.

Fig. Shapes of 2p

Fig. Shapes of 2p_x_x, 2p, 2p_y_y and 2p and 2p_z_z orbitals orbitals

4.What do you mean by oxidation number? 4.What do you mean by oxidation number?

Oxidation number is defined as the actual or apparent charge possessed by an atom of the element in a Oxidation number is defined as the actual or apparent charge possessed by an atom of the element in a compound.

compound.

5.Calculate the oxidation number of 5.Calculate the oxidation number of

(a) Cr in K

(a) Cr in K₂₂CrCr₂₂OO₇₇ Solution:

Solution: Oxidation of K is +1, and oxygen is – 2. Oxidation of K is +1, and oxygen is – 2.

∴

2 2 (1) + (1) + 2Cr + 2Cr + 7 7 × × – – 2 2 = = 00 2 2 + + 2Cr 2Cr – – 14 14 = = 00 2Cr 2Cr – – 12 12 = = 00 2Cr 2Cr = = + + 1212 +12 +12 Cr = Cr = ---2 2 Cr Cr = = + + 66

∴

The oxidation number of Cr in KThe oxidation number of Cr in K22CrCr22OO77 is +6 is +6

(b) Cl in ClO (b) Cl in ClO₃₃––

Solution:

Solution: Oxidation number of oxygen is – 2. Oxidation number of oxygen is – 2. Cl O Cl O₃₃ = = – – 11 Cl Cl + + 3 3 × × – – 2 2 = = – – 11 Cl Cl – – 6 6 = = – – 11 Cl Cl = = – – 1 1 + + 66 Cl Cl = = + + 55

∴

The oxidation number of Cl in ClOThe oxidation number of Cl in ClO33-- is +5 is +5

(c) S in Na (c) S in Na₂₂SS₂₂OO₃₃ Solution:

Solution: Oxidation number of Na is +1, Oxygen is –2. Oxidation number of Na is +1, Oxygen is –2. Na Na₂₂SS₂₂OO₃₃ = = 00 2 2 × 1 × 1 + + 2S 2S + + 3 3 × × – – 2 2 = = 00 2p 2pxx X X Z Z 2p 2pyy X X Z Z 2p 2pzz X X Z Z Y Y Y Y Y Y

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2 2 + + 2S 2S – – 6 6 = = 00 2S 2S – – 4 4 = = 00 2S 2S = = + + 44 S S = = 4 4 / / 22 S S = = + + 22

∴

The oxidation number of S in NaThe oxidation number of S in Na22SS22OO33 is +2 is +2

III. ANSWER IN BRIEF (T.B. Page 21) III. ANSWER IN BRIEF (T.B. Page 21)

1.State Aufbau’s principle. 1.State Aufbau’s principle.

“Electrons are filled in the increasing order of energy level” “Electrons are filled in the increasing order of energy level”

According to this principle first the electrons occupy the orbitals with lowest energy. This is decided by the According to this principle first the electrons occupy the orbitals with lowest energy. This is decided by the sum of the principle quantum number and azimuthal quantum number. This is called (

sum of the principle quantum number and azimuthal quantum number. This is called ( nn + + ll) rule.) rule. Rule 1:

Rule 1: The electrons first occupy that orbital for which (The electrons first occupy that orbital for which ( nn + +ll) value is lowest.) value is lowest. Rule 2:

Rule 2: When (When (nn ++ll) values for two orbitals are equal, then the electrons first occupy the orbital with lower) values for two orbitals are equal, then the electrons first occupy the orbital with lower value of

value of nn..

2.State Pauli exclusion principle with an illustration. 2.State Pauli exclusion principle with an illustration.

“In an atom no two electrons can have the same set of four quantum numbers”. “In an atom no two electrons can have the same set of four quantum numbers”. Illustration of Pauli's exclusion principle:

Illustration of Pauli's exclusion principle: 1.

1. In In an atom if an atom if one electron is one electron is assignassigned ed a set a set of four quantum of four quantum numbersnumbers nn = 1, = 1, ll = 0,= 0, mm = 0, = 0, ss = + ½, then other = + ½, then other electrons

electrons cannot be assignedcannot be assigned the same set of quantum numbers. the same set of quantum numbers. 2.

2. If three qIf three quantum numbers for two euantum numbers for two electrolectrons are the ns are the same, then these electrons must hsame, then these electrons must have different fourthave different fourth quantum number.

quantum number. n

n l l mm s s First

First electron electron 1 1 0 0 0 0 + + ½½ Second

Second electron electron 1 1 0 0 0 0 – – ½½

3.Give the difference between orbit and orbital. 3.Give the difference between orbit and orbital.

Difference between an orbit and an orbital Difference between an orbit and an orbital

ORBIT ORBITAL

1.

1. It It is is a a definite definite circulacircular r path path in in It It is is the the three three dimensional dimensional regionregion which

which the the electrelectron on is is supposed supposed around around the the nucleus nucleus in in whichwhich to

to revolve revolve around around the the nucleus. nucleus. there there is is maximum maximum probabiprobabilitylity of finding the electron.

of finding the electron. 2.

2. It It is is circular circular in in shape. shape. It It has has different different three three dimensiondimensionalal shapes.

shapes. Eg. Eg. ‘ ‘ss’-orbitals are’-orbitals are spherical,

spherical, p p-orbitals are dump-orbitals are dump bell shaped etc.

bell shaped etc. 3.

3. An An orbit orbit can can contain contain a a maximum maximum An An orbital orbital can can contain contain aa 2

2nn22_{electrons where}_{electrons where n}_n_represents_represents _maximum_{maximum of}_{of only}_{only 2}_{2 electrons.}_electrons.

the order of the orbit from the order of the orbit from the nucleus.

the nucleus. 4. The

4. The position position and and momentum momentum It It is is not not possible possible to to find find thethe of

of the the electrelectron on can can be be calculacalculated ted exact exact position position and and momentummomentum at

at the the same same time. time. of of the the electron electron at at the the same same time.time.

5.

5. They They are are designatdesignated ed as as K, K, L, L, M, M, N N etc etc They They are are designatdesignated ed as as s, s, p, p, d, d, f f etcetc

4.Explain spin quantum number. 4.Explain spin quantum number.

Spin Quantum Number ( Spin Quantum Number ( s s):): 1.

1. It represents It represents the dithe direction of the rection of the spin of the spin of the electrons.electrons. 2.

2.It is denoted by the symbol s.It is denoted by the symbol s. 3.

3.The electron may spin in the clockwiseThe electron may spin in the clockwise

↑

↑↑

↑

direction or anticlockwise direction or anticlockwise

↓

↓↓

↓

direction. And hence it can have only direction. And hence it can have only two values namely either + ½ or –½.

two values namely either + ½ or –½. 4.

4. Two electronTwo electrons with the same sign of spin s with the same sign of spin are said to have parallel spinare said to have parallel spins and are represented bys and are represented by

↓↓

(or) (or)

↑↑

while those having opposite spins are said to have anti parallel spins

↑↓

and are known as paired up and are known as paired up electrons.

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5.Write a note on Sommerfeld model of atom. 5.Write a note on Sommerfeld model of atom.

According to Sommerfeld, the electron moving around the nucleus must describe an elliptical orbit in According to Sommerfeld, the electron moving around the nucleus must describe an elliptical orbit in addition to circular one as suggested by Bohr.

addition to circular one as suggested by Bohr. n n ₌₌_3,_3,kk ₌₌₃₃ n n ₌₌_3,_3,kk₌₌₂₂ n n ₌₌_3,_3,kk₌₌₁₁

Fig .Bohr Sommerfeld orbits for n = 3, k = 1,2,3 Fig .Bohr Sommerfeld orbits for n = 3, k = 1,2,3

Note:

Note: Both Both nn and and k k are integers. When the value of are integers. When the value of k k is equal to is equal to nn, the orbit is circular, but for other, the orbit is circular, but for other values of

values of k k , the orbit is elliptical., the orbit is elliptical.

IV. ANSWER IN DETAIL.(T.B. Page 21) IV. ANSWER IN DETAIL.(T.B. Page 21)

1.

1. Discuss the Discuss the four types four types of of quantum numbers quantum numbers in in detail.detail.

The numbers which designate and distinguish various atomic orbitals and electrons present in an atom are The numbers which designate and distinguish various atomic orbitals and electrons present in an atom are called quantum numbers.

called quantum numbers.

In an atom, the state of each electron is different with respect to the nucleus. In order to define the state of the In an atom, the state of each electron is different with respect to the nucleus. In order to define the state of the electron completely, four quantum numbers are

electron completely, four quantum numbers are used.used. They are

They are -1.

1. Principal quantum number (Principal quantum number (nn)) 2.

2. Azimuthal quantum number (Azimuthal quantum number (ll)) 3.

3. Magnetic quantum number (Magnetic quantum number (mm)) 4.

4. Spin quantum number (Spin quantum number (ss).). 1.

1. Principal Quantum Number (Principal Quantum Number ( n n):): 1.

1. It determines the energy shell It determines the energy shell in which the in which the electrelectron is on is revolving around the nucleus. It is also revolving around the nucleus. It is also known as mknown as majorajor energy level.

energy level. 2.

2. It is denoted It is denoted by the symbol n by the symbol n and may have any and may have any integraintegral value el value except zerxcept zero.o. i.e.,i.e., it can have the value it can have the value nn =1,2,3, …. etc.

=1,2,3, …. etc. 3.

3. The The valuevalue nn = 1 denotes that the electron is in the first shell (K shell). = 1 denotes that the electron is in the first shell (K shell). The value

The value nn = 2 denotes that the electron is in the second shell (L shell). = 2 denotes that the electron is in the second shell (L shell). The value

The value nn = 3 denotes that the electron is in the third shell (M shell).= 3 denotes that the electron is in the third shell (M shell). The value

The value nn = 4 denotes that the electron is in the fourth shell (N shell).= 4 denotes that the electron is in the fourth shell (N shell). 4.

4. As As the distance of the distance of the electron from the electron from the nucleus increases, its energy becomes the nucleus increases, its energy becomes higher and hihigher and higher.gher. 5.

5. The maximum nThe maximum number of electrons in umber of electrons in a major enea major energy level is given rgy level is given by 2by 2nn22_..

Principal quantum Principal quantum

number ‘n’ number ‘n’

Designation

Designation Maximum Maximum numbernumber of electrons (2n of electrons (2n22)) 1 1 2 2 3 3 4 4 K K L L M M N N 2 2 8 8 18 18 32 32

2. Azimuthal Quantum Number or Orbital Quantum Number ( 2. Azimuthal Quantum Number or Orbital Quantum Number ( l l ):):

1.

1. It It represents represents thethe sub shellsub shell to which the electron belongs. to which the electron belongs. 2.

2. It It is is denoted by denoted by the the symbolsymbol ll. Its value depends on the principal quantum number. Its value depends on the principal quantum number nn. It may have any value. It may have any value ranging from 0 to (

ranging from 0 to (nn – 1).– 1). Principal quantum

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number

number ‘‘ n n’’ l l = ( = ( n n-1) -1) sub sub shells shells or or orbitalorbital 1 1 0 0 11ss 2 2 0 0 22ss 1 1 22 p p 0 0 33ss 3 3 1 1 33 p p 2 2 33d d 0 0 44ss 4 4 1 1 44 p p 2 2 44d d 3 3 44 f f 3.

3. The The valuevalue ll = 0 denotes that the electron is in the s sub shell or = 0 denotes that the electron is in the s sub shell or ss orbital. orbital. The value

The value ll = 1 denotes that the electron is in the p sub shell or = 1 denotes that the electron is in the p sub shell or p p orbital. orbital. The value

The value ll = 2 denotes that the electron is in the d sub shell or= 2 denotes that the electron is in the d sub shell or d d orbital. orbital. The value

The value ll = 3 denotes that the electron is in the f sub shell or = 3 denotes that the electron is in the f sub shell or f f orbital. orbital. 3. Magnetic Quantum Number (

3. Magnetic Quantum Number ( m m):): 1.

1. It It represents represents thethe orientationorientation of an atomic orbital in space. of an atomic orbital in space. 2.

2. It It is is denoted by denoted by the symbolthe symbol mm. The possible value which m can have depends upon the value of. The possible value which m can have depends upon the value of ll. It may have. It may have all the integral values between –

all the integral values between – l l to + to + l l through 0 that is the total number of values of m would be (2 through 0 that is the total number of values of m would be (2ll + 1).+ 1). 3.

3. Its value tellIts value tells the orientations the orientations of orbital in space. The vs of orbital in space. The value ofalue of mm = 0 denotes that the orbital has = 0 denotes that the orbital has nono orientation

orientation. The value of. The value of mm = 1 denotes that it has three orbital with= 1 denotes that it has three orbital with three typesthree types of orientations. The value of orientations. The value of

of mm = = 2 denotes that i2 denotes that it has five ot has five orbitarbital withl with five typesfive types of orientations. of orientations. Principal quantum

Principal quantum l l value value m m value value Name Name of of the the subsub number ‘

number ‘ n n’’ l l =( =( n n-1) -1) (-(- ll ..._O_O... ₊_{+ l}_l )₎ _{shells or}_shells_{or orbital}_orbital

with orientation with orientation 1 1 0 0 0 0 11ss 2 2 0 0 0 0 22ss 1 1 – – 1, 1, 0, 0, + + 1 1 22 p p_x_x, 2, 2 p p_y_y, 2, 2 p p_zz 0 0 0 0 33ss 3 3 1 1 – – 1, 1, 0, 0, + + 1 1 33 p p_x_x, 3, 3 p p_y_y, 3, 3 p p_zz 2 2 – – 2, 2, – – 1, 1, 0, 0, +1 +1 ,+2 ,+2 33d d _xy_xy, 3, 3d d _xz_xz, 3, 3d d _yz_yz,, 3 3d d zz22, 3, 3d d xx22_–_–yy22

4. Spin Quantum Number ( 4. Spin Quantum Number ( s s):):

1.

1. It represents It represents the dithe direction of the rection of the spin of the spin of the electrons.electrons. 2.

2.It is denoted by the symbol s.It is denoted by the symbol s. 3.

3.The electron may spin in the clockwiseThe electron may spin in the clockwise

↑

↑↑

↑

direction or anticlockwise direction or anticlockwise

↓

↓↓

↓

direction. And hence it can have only direction. And hence it can have only two values namely either + ½ or –½.

two values namely either + ½ or –½. 4.

4. Two electronTwo electrons with the same sign of spin s with the same sign of spin are said to have parallel spinare said to have parallel spins and are represented bys and are represented by

↓↓

(or) (or)

↑↑

while those having opposite spins are said to have anti parallel spins

↑↓

and are known as paired up and are known as paired up electrons.

electrons.

2.State and explain Hund’s rule and Pauli’s exclusion principle with suitable illustrations. 2.State and explain Hund’s rule and Pauli’s exclusion principle with suitable illustrations. Hund’s Rule:

Hund’s Rule: “Among the orbitals of same energy, electrons do not start pairing, until all these orbitals are“Among the orbitals of same energy, electrons do not start pairing, until all these orbitals are singly occupied”.

singly occupied”.

Hund’s rule is also called as the

Hund’s rule is also called as the principlprinciple of minimum e of minimum pairing and pairing and the principle of maximum multiplicity.the principle of maximum multiplicity. Example I:

Example I: In the case of nitrogen, there ar In the case of nitrogen, there are 3 electrons to be filled in 2e 3 electrons to be filled in 2 p p_x_x, 2, 2 p p_y_yand 2and 2 p p_zz orbitals According to Hund’s orbitals According to Hund’s rule one electron will be filled in each one of these degenerate orbitals as 2

rule one electron will be filled in each one of these degenerate orbitals as 2 p p_x_x11_{, 2}_{, 2 p}_p y y 1 1_{, 2}_{, 2 p}_p zz 1 1_.. 1 1ss22 ₂_2ss22 ₂_2 p_p x x 22 p pyy 22 p pzz Example II:

Example II: In the case of oxygen, there are 4 electrons to be filled in 2In the case of oxygen, there are 4 electrons to be filled in 2 p p_x_x, , 22 p p_y_y and 2 and 2 p p_z_zorbitals. In this case theorbitals. In this case the numbe

number of r of electrons exceeds the number of orbitals. According to Hund’s rule, electrons exceeds the number of orbitals. According to Hund’s rule, each one of 2peach one of 2p_x_x, 2p, 2p_y_y and 2p and 2p_zz is singly is singly occupied. Afterwards, the fourth electron is filled in one of the singly occupied orbitals, but the spins of these two occupied. Afterwards, the fourth electron is filled in one of the singly occupied orbitals, but the spins of these two electrons must be opposite (

electrons must be opposite (

↑↓

). This is shown as 2). This is shown as 2 p p_x_x22_{, 2}_{, 2 p}_p y y 1 1_{, 2}_{, 2 p}_p zz 1 1_.. ↑↓ ↑↓ ↑↓↑↓ ↑↑ ↑↑ ↑↑

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1

1ss22 ₂_2ss22 ₂_2 p_p x

x 22 p pyy 22 p pzz

“In an atom no two electrons can have the same set of four quantum numbers”. “In an atom no two electrons can have the same set of four quantum numbers”. Illustration of Pauli's exclusion principle:

Illustration of Pauli's exclusion principle: 1.

1. In In an atom if an atom if one electron is one electron is assignassigned ed a set a set of four quantum of four quantum numbersnumbers nn = 1, = 1, ll = 0,= 0, mm = 0, = 0, ss = + ½, then other = + ½, then other electrons

electrons cannot be assignedcannot be assigned the same set of quantum numbers. the same set of quantum numbers. 2.

2. If three qIf three quantum numbers for two euantum numbers for two electrolectrons are the ns are the same, then these electrons must hsame, then these electrons must have different fourthave different fourth quantum number.

quantum number. n

n l l mm s s First

First electron electron 1 1 0 0 0 0 + + ½½ Second

Second electron electron 1 1 0 0 0 0 – – ½½ 3.Discuss the shapes of

3.Discuss the shapes of s s and and p p orbitals with a neat diagram. orbitals with a neat diagram. s

s orbital: orbital: 1.

1. s orbis orbital is tal is spherically spherically symmetric symmetric around the naround the nucleus,ucleus, i.e.,i.e., probability of finding the electron at a particular probability of finding the electron at a particular distance from the nucleus is the same in all directions.

distance from the nucleus is the same in all directions. 2.

2. 11ss orbital does not contain any node and is the smallest of all subsequent orbital does not contain any node and is the smallest of all subsequent ss orbitals. The size of an orbitals. The size of an ss orbital orbital increases with increase in the value of

increases with increase in the value of nn.. 3.

3. 22ss orbital is larger in size as compared to 1 orbital is larger in size as compared to 1ss orbital possesses a node. The 3 orbital possesses a node. The 3ss orbital still larger in size and orbital still larger in size and contains two nodes. The shapes of 1

contains two nodes. The shapes of 1ss, 2, 2ss and 3 and 3ss orbitals are shown in orbitals are shown in FigFig..

1

1 s s Orbital Orbital 22 s s Orbital Orbital 33 s s Orbital Orbital

Fig. Shapes of 1s, 2s and 3s orbitals Fig. Shapes of 1s, 2s and 3s orbitals

p

p orbitals: orbitals: 1.

1. p p-orbital has three orientations-orbital has three orientations i.e.i.e. probability of finding probability of finding p p-electron is along mutually perpendicular X, Y and-electron is along mutually perpendicular X, Y and Z axis. These orbitals are thus named as

Z axis. These orbitals are thus named as p p_x_x,, p p_y_y ,and ,and p p_zzorbital.orbital. 2. In

2. In p p_x_x orbital, the electron density is distributed along X-axis while in orbital, the electron density is distributed along X-axis while in p p_y_y and and p p_zz orbitals, the electron density orbitals, the electron density distributi

distributions are along Y aons are along Y and Z axes rnd Z axes respectivelyespectively.. 3. Each

3. Each p p orbital is dumb bell shaped and consists of two lobes of electron cloud which extend outwards and orbital is dumb bell shaped and consists of two lobes of electron cloud which extend outwards and away from the nucleus along the axial line.

away from the nucleus along the axial line. 4.

4. A nodal plane exiA nodal plane exists between the two lobests between the two lobes. Along this planes. Along this plane, the probability of finding ele, the probability of finding electron (ctron (

ψ

22_{) is zero}_{) is zero}

and consequently the electron density is also zero. and consequently the electron density is also zero. 5.

5. In In eacheach p p orbital, orbital, the point at which the two lobes meet together is a nodal pointthe point at which the two lobes meet together is a nodal point. It is the point from. It is the point from which the nodal plane passes. The shapes of 2

which the nodal plane passes. The shapes of 2 p p_x_x, 2, 2 p p_y_y and 2 and 2 p p_zz orbitals are shown in Fig orbitals are shown inFig..

Fig.

Fig. Shapes Shapes of 2pof 2p_x_x, 2p, 2p_y_y and 2p and 2p_z_z orbitals orbitals

Nodes are the region in which probability of finding electrons (

ψ

22_{) is zero.}_{) is zero.}

The above four quantum numbers give the position of any electron in the major energy level, the The above four quantum numbers give the position of any electron in the major energy level, the

orientation of electron in the orbital and the direction of its spin. The various states that an electron can orientation of electron in the orbital and the direction of its spin. The various states that an electron can occupy are summarized in the table given below.

occupy are summarized in the table given below.

↑↓

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↑

↑↓

↑

↑↓

↑

↓

↑

↑↓

↑

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69. The principal quantum number of an atom represents 69. The principal quantum number of an atom represents

(a)

(a) Size Size of of orbital orbital (b) (b) spin spin angular angular momentummomentum (c)

(c) Orbital Orbital angular angular momentum momentum (d) (d) space space orientation orientation of of the the orbitalorbital 70. The maximum number of electrons in an atom which can have n = 4 is 70. The maximum number of electrons in an atom which can have n = 4 is

(a)

(a) 4 4 (b) (b) 8 8 (c) (c) 16 16 (d) (d) 3232 71. The maximum value of

71. The maximum value of ll for an electron in fifth energy level is for an electron in fifth energy level is (a)

(a) 5 5 (b) (b) 4 4 (c) (c) 3 3 (d) (d) 22

72. If the value of principal quantum number is 3, the total possible values for magnetic quantum number 72. If the value of principal quantum number is 3, the total possible values for magnetic quantum number

will be will be

(a)

(a) 1 1 (b) (b) 4 4 (c) (c) 9 9 (d) (d) 1212 73. Azimuthal quantum number of last electron of

73. Azimuthal quantum number of last electron of 1111Na isNa is

(a)

(a) 1 1 (b) (b) 2 2 (c) (c) 3 3 (d) (d) 00 74. The correct set of quantum numbers for the unpaired electron of chlorine atom is 74. The correct set of quantum numbers for the unpaired electron of chlorine atom is

n n ll mm (a) (a) 2 2 1 1 00 (b) (b) 2 2 1 1 11 (c) (c) 3 3 1 1 11 (d) (d) 3 3 0 0 11

5. Which quantum number will determine the shape of the sub shell? 5. Which quantum number will determine the shape of the sub shell?

(a)

(a) Principal Principal quantum quantum number number (b) (b) azimuthal azimuthal quantum quantum numbernumber (c)

(c) Magnetic Magnetic quantum quantum number number (d) (d) Spin Spin quantum quantum numbernumber 76. The four quantum numbers of valence electron of potassium are 76. The four quantum numbers of valence electron of potassium are

(a)

(a) 4,0,1, 4,0,1, 1/2 1/2 (b) (b) 4,1,0,1/2 4,1,0,1/2 (c) (c) 4,0,0, 4,0,0, 1/2 1/2 (d) (d) 4,1,1,1/24,1,1,1/2

77. An electron is present in 4f sub-shell. The possible values of azimuthal quantum number for this 77. An electron is present in 4f sub-shell. The possible values of azimuthal quantum number for this

electron are electron are

(a)

(a) 0,1,2,3 0,1,2,3 (b) (b) 1,2,3,4 1,2,3,4 (c) (c) 3 3 (d) (d) 44 78. Which of the following electronic configuration is correct?

78. Which of the following electronic configuration is correct? (a) 1s

(a) 1s22, 2s, 2s22, 2p, 2pxx22, 2p, 2pyy22, 2p, 2pzz22, 3s, 3s22,3p,3pxx22 (b) 1s(b) 1s22, 2s, 2s11, 2p, 2pxx11, 2p, 2pyy11, 2p, 2pzz11

(c) 1s

(c) 1s22, 2s, 2s22, 2p, 2p66, 3s, 3s22, 3p, 3p66, 3d, 3d44,4s,4s22 (d) 1s(d) 1s22, 2s, 2s22, 2p, 2p66, 3s, 3s22, 3p, 3pxx11, 3p, 3pyy11,3p,3pzz11

79. Which of the following is not true for a principal energy level having n = 3? 79. Which of the following is not true for a principal energy level having n = 3?

(a)

(a) There There are are three three sub-shells sub-shells (b) (b) There There are are nine nine orbitalorbital (c)

(c) There There are are a a maximum maximum of of 18 18 electrons electrons (d) There (d) There are are six six electrons electrons withwith ll = 2 = 2 80. The maximum number of electrons in p-orbital with n = 6 m = 0 is

80. The maximum number of electrons in p-orbital with n = 6 m = 0 is (a)

(a) 2 2 (b) (b) 6 6 (c) (c) 10 10 (d) (d) 1414 81. Which of the following sets of quantum numbers is correct?

81. Which of the following sets of quantum numbers is correct? (a) n = 4, (a) n = 4, ll= = 3, 3, m m = = + + 4, 4, x x = = +1/2 +1/2 (b) n (b) n = = 3,3, ll = 2, m = + 3, s = -1/2 = 2, m = + 3, s = -1/2 (c) n = 2, (c) n = 2, ll= 2, = 2, m m = = + + 2, 2, s s = = +1/2 +1/2 (d) (d) n n = = 1,1,ll = 0, m = 0, s = -1/2 = 0, m = 0, s = -1/2 82. For n = 4 82. For n = 4

(a) the total possible values of

(a) the total possible values of ll are are 3 3 (b) (b) the the highest highest value value ofof ll is 4 is 4 (c) the total number of possible values of

(c) the total number of possible values of mm is is 7 7 (d) (d) the the highest highest value value ofof mm is + 3 is + 3 83. Which of the following orbital designation is not possible

83. Which of the following orbital designation is not possible (a) 5

(a) 5 f f (b) (b) 5g 5g (c) (c) 77 p p (d) (d) 33 f f

84. Nitrogen has the electronic configuration 1s

84. Nitrogen has the electronic configuration 1s22 2s 2s22 2p 2p11xx 2p 2p11yy 2p 2p11zz and not 1s and not 1s22 2s 2s22 2p 2p22xx 2p 2p11yy 2p 2p00zz. This is. This is

determined by determined by

(a)

(a) Pauli’s Pauli’s exclusion exclusion principle principle (b) (b) Aufbau Aufbau principleprinciple (c)

(c) uncertainty uncertainty principle principle (d) (d) Hund’s Hund’s rulerule 85. The set of quantum numbers

85. The set of quantum numbers nn,, 11 and andmm for the valence electron of sodium (atomic number 11) is for the valence electron of sodium (atomic number 11) is (a)

(a) 3, 3, 0, 0, 0 0 (b) (b) 3, 3, 2, 2, 1 1 (c) (c) 3, 3, 2, 2, -2 -2 (d) (d) 2, 2, 1, 1, -1-1 86. The azimuthal quantum number value for 3p electron is

86. The azimuthal quantum number value for 3p electron is (a)

(a) 3 3 (b) (b) 2 2 (c) (c) 1 1 (d) (d) 00

87. The fact that an orbital can accommodate a maximum of two electrons is deduced from 87. The fact that an orbital can accommodate a maximum of two electrons is deduced from

(a)

(a) Hund’s Hund’s rule rule (b) (b) Pauli’s Pauli’s exclusion exclusion principleprinciple (c)

(c) Aufbau Aufbau principle principle (d) (d) uncertainty uncertainty principleprinciple 88. Which of the following value of

88. Which of the following value of 11 is not possible for n = 4? is not possible for n = 4? (a)

(a) 2 2 (b) (b) 1 1 (c) (c) 3 3 (d) (d) 44 89. The number of orbitals in n = 3 quantum level is

89. The number of orbitals in n = 3 quantum level is (a)

(a) 6 6 (b) (b) 18 18 (c) (c) 9 9 (d) (d) 1212 90. The set of quantum numbers not applicable to an electron in an atom is

90. The set of quantum numbers not applicable to an electron in an atom is (a) n = 1,

(a) n = 1, ll= 0, = 0, m m = = 0, 0, s s = = + + ½ ½ (b) (b) n n = = 1,1, ll = 1, m = 0, s = + ½ = 1, m = 0, s = + ½ (c) n = 1,

(c) n = 1, ll= 0, = 0, m m = = 0, 0, s s = = - - ½ ½ (d) (d) n n = = 2,2,ll = 1, m = 1, s = + ½ = 1, m = 1, s = + ½ 91. The energy of an electron is mainly determined by

91. The energy of an electron is mainly determined by (a)

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(c)

(c) magnetic magnetic quantum quantum number number (d) (d) spin spin quantum quantum numbernumber 92. The number of orbitals possible in a sub-shell with

92. The number of orbitals possible in a sub-shell with 11 = 3 is = 3 is (a)

(a) 3 3 (b) (b) 5 5 (c) (c) 6 6 (d) (d) 77 93. Maximum number of electrons that can be placed in 2p sub-shell is

93. Maximum number of electrons that can be placed in 2p sub-shell is (a)

(a) 2 2 (b) (b) 4 4 (c) (c) 6 6 (d) (d) 88 94. Among the following which is the correct outermost configuration of Cu atom? 94. Among the following which is the correct outermost configuration of Cu atom?

(a) 4s

(a) 4s22 3d 3d99 (b) (b) 4s4s11 3d 3d1010 (c) 4s(c) 4s11 3d 3d99 (d) (d) 4s4s11 3d 3d88 95. The oxidation number of S in S

95. The oxidation number of S in S-2-2 is: is: (a)

(a) –2 –2 (b) (b) 0 0 (c) (c) –6 –6 (d) (d) +2+2 96. Magnetic quantum number specifies

96. Magnetic quantum number specifies (a)

(a) size size of of orbitals orbitals (b) (b) shape shape of of orbitalsorbitals (c)

(c) orientatorientation ion of of orbitals orbitals in in space space (d) (d) spin spin angular angular momentummomentum 97. Magnetic quantum number for the last electron in potassium is

97. Magnetic quantum number for the last electron in potassium is (a)

(a) 0 0 (b) (b) 1 1 (c) (c) 2 2 (d) (d) 33 98. Oxidation may be defined as:

98. Oxidation may be defined as: (a)

(a) Addition Addition of of electron electron (b) Gain (b) Gain of of electroelectronn (c)

(c) Addition Addition of of hydrogen hydrogen (d) (d) Addition Addition of of oxygenoxygen 99. In an oxidation process, oxidation number:

99. In an oxidation process, oxidation number:

(a)

(a) Decreases Decreases (b) (b) IncreasesIncreases (c)

(c) Does Does not not change change (d) (d) First First increases increases then then decreasesdecreases

100. The process in which oxidation number increases is known as: 100. The process in which oxidation number increases is known as:

(a)

(a) Oxidation Oxidation (b) (b) Reduction Reduction (c) (c) Auto Auto oxidation oxidation (d) (d) None None of of the the aboveabove 101. The oxidation number of hydrogen in LiH is:

101. The oxidation number of hydrogen in LiH is: (a)

(a) +1 +1 (b) (b) –1 –1 (c) 2 (c) 2 (d) (d) 00 102. The oxidation number of oxygen in O

102. The oxidation number of oxygen in O22 molecule is: molecule is:

(a)

(a) 0 0 (b) (b) –1/2 –1/2 (c) (c) –2 –2 (d) (d) +2+2 103. Oxidation State of oxygen in hydrogen peroxide is:

103. Oxidation State of oxygen in hydrogen peroxide is: (a)

(a) –1 –1 (b) (b) +1 +1 (c) 0 (c) 0 (d) (d) –2–2 104. The Oxidation State of chlorine in KClO

104. The Oxidation State of chlorine in KClO44 is: is:

(a)

(a) –1 –1 (b) (b) +1 +1 (c) +7 (c) +7 (d) (d) –7–7 105. The Oxidation State of Mn in K

105. The Oxidation State of Mn in K22MnOMnO44 is: is:

(a)

(a) +6 +6 (b) (b) –6 –6 (c) +2 (c) +2 (d) (d) –2–2 106. The oxidation number of N in NH

106. The oxidation number of N in NH33 is: is:

(a) (a) +3 +3 (b) (b) –3 –3 (c) +5 (c) +5 (d) (d) 00 _____________________________________________________________________________________ _____________________________________________________________________________________ Answers: Answers: 1.

1. (b) (b) 2. 2. (c) (c) 3. 3. (d) (d) 4. 4. (a) (a) 5. 5. (d) (d) 6. 6. (d) (d) 7. 7. (c) (c) 8. 8. (a) (a) 9. 9. (c) (c) 10. 10. (b) (b) 11. 11. (c) (c) 12. 12. (d) (d) 13. 13. (c)(c) 14. (d) 15. (d) 16. (d) 17. (b) 18. (b) 19. (a) 20. (c) 21. (d) 22. (d) 23. (d) 24. (c) 25. (a) 26. (c) 14. (d) 15. (d) 16. (d) 17. (b) 18. (b) 19. (a) 20. (c) 21. (d) 22. (d) 23. (d) 24. (c) 25. (a) 26. (c) 27. (b) 28. (a) 29. (a) 30. (b) 31. (b) 32. (c) 33. (a) 34. (d) 35. (d) 36. (a) 37. (a) 38. (c) 39. (d) 27. (b) 28. (a) 29. (a) 30. (b) 31. (b) 32. (c) 33. (a) 34. (d) 35. (d) 36. (a) 37. (a) 38. (c) 39. (d) 40. (a)

40. (a) 41. (c) 41. (c) 42. (a) 42. (a) 43. (b) 43. (b) 44. (b) 44. (b) 45. (a) 46. (b) 47. (a) 4845. (a) 46. (b) 47. (a) 48. (b) 49. (c. (b) 49. (c) ) 50. (b) 51. (a) 52. (c)50. (b) 51. (a) 52. (c) 53. (c) 54. (a) 55. (a) 56. (c) 57

53. (c) 54. (a) 55. (a) 56. (c) 57. (a) 58. (d) 59. . (a) 58. (d) 59. (c) 60. (c) 61(c) 60. (c) 61. (c) . (c) 62. (a) 63. (a) 64. (b) 65. (b62. (a) 63. (a) 64. (b) 65. (b)) 66. (c) 67. (b) 68. (b) 69. (a) 70. (d) 71. (b) 72. (c) 73. (d) 74. (c) 75. (b) 76. (c) 77. (c) 78. (d) 66. (c) 67. (b) 68. (b) 69. (a) 70. (d) 71. (b) 72. (c) 73. (d) 74. (c) 75. (b) 76. (c) 77. (c) 78. (d) 79. (d) 80. (b) 81. (d) 82. (c) 83. (b) 84. (d) 85. (a) 86. (c) 87. (b) 88. (d) 89. (b) 90. (b) 91. (a) 79. (d) 80. (b) 81. (d) 82. (c) 83. (b) 84. (d) 85. (a) 86. (c) 87. (b) 88. (d) 89. (b) 90. (b) 91. (a) 92. (d) 93. (c) 9

92. (d) 93. (c) 94. (b) 95. (a) 964. (b) 95. (a) 96. (c) 97. (a) . (c) 97. (a) 98. (d) 99. (b) 100. (a) 10198. (d) 99. (b) 100. (a) 101. (b) 102. (b) 102. (a) 103. (a) 103. (a). (a) 104. (c) 105. (a) 106. (b)

104. (c) 105. (a) 106. (b)

_____________________________________________________________________________________ _____________________________________________________________________________________ I. ANSWER IN ONE OR TWO SENTENCES:

I. ANSWER IN ONE OR TWO SENTENCES: 1. What is meant by an anu?

1. What is meant by an anu?

If an element is broken down into smaller and smaller and the process would end at the smallest If an element is broken down into smaller and smaller and the process would end at the smallest particle which cannot be broken any further and this particle is called an anu.

particle which cannot be broken any further and this particle is called an anu.

2. What is an atom? 2. What is an atom?

An atom is an extremely small and indivisible particle. All matters are composed of such very tiny An atom is an extremely small and indivisible particle. All matters are composed of such very tiny particles called atoms. Atom is a Greek word that means indivisible.

particles called atoms. Atom is a Greek word that means indivisible.

3. Why Principal quantum number is ca

3. Why Principal quantum number is ca lled as major energy level?lled as major energy level?

Principal quantum number determines the energy shell in which the electron is revolving around Principal quantum number determines the energy shell in which the electron is revolving around the nucleus. Hence it is also known as major energy level.