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Blazing goIITian

Joined:	26 Feb 2007
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17 Apr 2007 08:35:42 IST

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SHORT NOTES & OBJ Q'S...ATOMIC STRUCTURE

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ATOMIC STRUCTURE

John Dalton in 1803 suggested that all matter is made up of small invisible particle is called atoms. However modern experimental evidences proved that an atom still contains small particles is called fundamental particles of atoms. The most important fundamental particles, electrons, protons and neutrons are present in atoms of all elements except hydrogen which contains only electron and proton

Rutherford Model of Atom.

Rutherford performed alpha particles scattering experiment and concluded that total mass and total positive charge of atom is concentrated in the small nucleus of radius 10^{-14- 10-15 m.}

Around this nucleus electrons rotate in circular orbit the mass of hydrogen nucleus(Proton) was found to be 1.67 ´10-27 kg which was 1837 times more heavier than electron it has been observed that there are some other particle also like positron, neutrino, meson and antiproton etc but it does not mean that all nuclei of atoms of different in elements will contain all these fundamental particle. In fact these are produced in nucleus during transformation of mass into energy and energy into mass.

Characteristics of Fundamental Particle

^Particle	^Symbol	^Mass	^Discoverer	^charge
^Electron	^-1eo	^{9.1 ´10-31 kg 0.000548 a.m.u or 1/1837 of that of hydrogen atom}	^J.J.Thomson	^{-1 charge or (-)1.602´10-19 coulombs}
^Proton	^{P or _1H1}	^{_{1.672 ´10-27 kg 1.00728 a.m.u}}	^{_{Gold stein}}	^{_{+1 charge or (+)1.602´10-19 coulomb}}
^_Neutron	^_n	^{_{1.675´10-27 kg 1.00866a.m.u}}	^{_{J Chadwick}}	^{_{Neutral(0 charge) unstable particle n P +e + g}}
^_Positron	^{_{+1 eo}}	^{_{9.1 ´ 10-31 kg 0.000548amu}}	^_Anderson	^{_{+1 charge}}
^_Neutrino	^{_{0e0 or g}}	^{_{0.00002 amu (less than the mass of electron)}}	^_Pauli	^{_{Zero charge}}
^_Antiproton	^_P-	^_1.00728amu	^_Chamberlain	^{_{-1 charge}}
^_Meson	^{_{p ±,p 0 and m ±}}	^{_{276 electron mass (1 electron mass = 0.00055 a.m.u)}}	^_Yukawa	^{_{+ ve, -ve, or neutral in nature}}

^{_{Atomic number and mass number}}

Moseley gave a relation between the frequency of X ?rays emitted from the metal when beam of high speed electrons is bombarded on it and the atomic number(Z) of metal. The Moseley?s relation is ?n = a(Z-b)

Where n is the frequency of X ?rays, a, b are constants. The mass number of an element is the sum of neutrons and protons in the nucleus of atom and it is denoted by A. The

element X can be represented as ZX

mass number (A ) = number of protons + number of neutrons.

Atomic number(Z) = No. of protons = No. of electrons

No. of neutrons = A ? Z

Bohr model of atom

Rutherford model of atom could not explain stability. Bohr modified the Rutherford model and suggested that stability of atom could be explained by Planck?s quantum theory. He made following postulates

Electron in an atom revolve around the nucleus in certain fixed circular orbits of definite energy without losing energy. These orbits are also called stationary states.

Electron can be move in only those orbits in which the angular momentum of revolving electron is an integral multiple of h/2p that is mvr = n h

2p .....(1)

where h = Planks constant(6.626 ´ 10-34 Js), n= 1,2,3.... m= mass of electron,

r = radius of orbit and v = velocity of electron in the orbit

(iii) For the circular motion of electron in an orbit, the electrostatic force of attraction

1 , Z e2 between moving electron and nucleus should be balanced by

4pÎ0 r2

centrifugal force mv2 thus mv2 = 1 Ze2 .....(ii)

r r 4pÎ0 r2

where Î0 is the primitivity of free space(8.85 ´10-12 C2 N ?1 m-2) Z is atomic number and e is the charge on proton.

1__ = 9 ´ 109 Nm2 C-2, C.G.S units values of 1__ = 1

4pÎ0 4pÎ0

(iv) When electron jumps from higher energy orbit to lower energy orbit, it losses energy which is equal to the difference in energy of two states. This energy lost appears in the form of radiation of frequency n.(energy = hnÊ = h ´ c)

(v) when electron jumps from n2 orbit of energy En2 to n1 orbit of energy En1, the difference of energy emitted is given by DE = hn-En2-En1......(iii)

Bohr theory could explain only one electron system that is atom containing Z proton the nucleus and only one electron revolving round it such as hydrogen atom, single ionized helium atom or doubly ionized lithium atom

Equation for radii of orbit of hydrogen atom

r= n2 h2__ ( 4pÎ0)..... (iv)

4p2Ze2m

From above equation it is clear that the radius of any orbit is directly proportional to the square of number of that orbit. For hydrogen atom , Z = 1. By substituting value of h, p, m and e, the radius of first orbit of hydrogen atom is o

= 1 ´ (6.62 ´ 10-27 ergs)2 ´1______= 0.529 ´10-8 cm =0.529A

4(3.14)2 ´(4.803 ´10-10esU)2 ´(9.1 ´10-28 g)

radius of second orbit(r2) = (2)2´0.529 A = 4r1

Equation for energy of orbit of hydrogen atom

En = -1 2p2Z2m e4 .......(v)

n2 ( 4pÎ0)2h2

The negative sign shows that as the value of n increases that is we move away from nucleus the energy of electron also increases.
For hydrogen atom the energy of electron in first orbit(n = 1) is E1 = -13 .6 eV. This energy can be converted into Joules by relation 1eV = 1.6´10-19 J

In the second orbit, E2 = -3.4eV

As we know from equation (iii)

DE = hn = En2-En1

= 1 2p2Z2me4

- n22 (4pÎ0)2h2

+ 1 2p2Z2me4

n12 (4pÎ0)2h2

h ´ c = 1___ 2p2Z2me4 1 - 1

l (4pÎ0)2 h2 n12 n12

1 = 1___ 2p2Z2me4 1 - 1

l (4pÎ0)2 h2 n12 n12

But 1 = n (wave number i.e. the number of waves per cm).

n = R 1 - 1_ ......(vi)

n12 n22

where R is called Rydberg?s constant

n R = 1___ 2p2Z2me4

(4pÎ0)2 ch3

For hydrogen atom in C.G.S. units,

R= 109678 cm-1

Equation for velocity of electron in an Orbit

From equation (i), the velocity of electron can be calculated.

mvr = n h

v = nh

2pmr

Putting value of r from equation from equation (iv)

r = n2h2(4pÎ0)2

4p2Ze2m

v = nh 4p2Ze2m___

2pm ´ n2h2(4pÎ0)2

= 2pZe2

nh(4pÎ0)

The velocity of electron in nth orbit of hydrogen atom

vn = 2.19 ´ 108 cm/sec

Velocity of electron in first orbit

v1 = 2.19 ´108 cm/sec

This velocity is about 1 th of the velocity of light

137

Similerly, velocity of electron in second orbit is

v2 = 2.19 ´108 cm/sec

Bohr?s Theory and Emission Spectra

Suppose an atom absorbs energy from its surroundings. This causes the electron to jump to higher energy level . The atom is now in an excited state. The electron, returns back almost immediately to one of the lower energy level(or ground state). The difference in the energy possessed by the electron in the higher level and the lower level is emitted by the atom in the form of line spectrum. Suppose higher energy level is associated with the energy En2 and lower with the energy En1

En2 ?En1 = hn

or n = (En2 ? En1)/h

or c/l = (En2 ? En1)/h

or l = hc___

(En2 ? En1)

n = frequency ; l = wavelength; c = velocity of radiation.

Since c and h are constant and En2-En has a definite value, each jump from one energy level to another will give rise to a spectral line of specific wavelength in the spectrum of hydrogen.

Since c and h are constant and En2 -En1 has a definite value, each jump from one energy level to another will give rise to a spectral line of specific wavelength in the spectrum of hydrogen.

Bohr's Theory and the Origin of Hydrogen Spectrum

Hydrogen atom contains only one electron. But spectrum consists of a large number of lines. Because a given sample of hydrogen contains a very large number of atoms of the order of a several millions. Suppose energy is supplied to this sample of the gas. Now different atoms will absorb different amounts of energy. The solitary electron in different atoms will, therefore, shift to different energy levels depending upon the In

energy absorbed by the atoms.

Series of lines of Hydrogen Spectrum

The spectrum of hydrogen atom contains five series of lines. Each of which is named after the name of its discoverer.

The series of line can be explained with the equation (vi),

n = 1 = R 1 - 1

l n12 n22

where Rydberg constant R= 109678 cm-1 for hydrogen atom.

Sommerfeld Extension of Bohr?s Theory

The use of high resolving power spectroscopes revealed the presence of fine structures(i.e., group of very fine lines)in the line spectra of hydrogen and hydrogen like atoms or ions. Bohr?s theory could not explain the occurrence of these fine line spectra. The thery was extended by Sommerfeld by putting forward the idea of elliptical orbits.

According to Sommerfeld an electron revolving around a central positively charged nucleus is in elliptical orbits. Thus according to Sommerfeld electrons move in elliptical orbits in place of circular orbits having the nuclei at one of the foci.

Electromagnetic Radiations

Which charged body is moved in magnetic field or a magnet in an electric field, electromagnetic radiations are produced. Ordinary light, X-rays and g -rays etc. are electromagnetic waves, these do not require any medium of propagation. Electromagnetic waves move with same velocity equal to velocity of light 3 ´1010 cm sec-1 but they differ in wavelengths and hence in frequencies. When sun light is passed through prism is separated into different colours each corresponds to the wave of

definite4 wavelength. The red light has highest wavelength(7600 A) while violet has

lowest wavelength(3800A)

The radioations which have wavelengths more than red light are known as infra red(IR) radiations. Similarly radiation with wavelength lower than that of violet light are known as ultra violet radiations. Radio waves are produced from alternating electric current of high frequency. These erlectromagnetic radiations are lowest frequency around 106 Hz(1 Hertz = 1 cycle per second)which are used for broadcasting. Microwaves are used for radar, their frequency is around 108 Hz. Infra red radiations(frequency @1013 Hz) are heat radiations. Ultraviolet waves(frequency = 1016 Hz) are component of sun?s radiations.

The arrangement of different types of electromagnetic radiation in decreasing order of the wavelengths or increasing order of their frequency termed electromagnetic spectrum. o

Common unit of length is Angstrom unit(A) which 10-8 cm or 10-10 m. To convert it into S.I unit suitable conversion are made accordingly.

1 Angstrom unit (A) = 102 pm (picometeres)

= 10-1 nm (nanometer)

The profixes to indicate power of ten have recommended for S.I. unit ? (i.e10-6

micro m 109) nano ? n; 10-12 pico-p) or 1 m m @1 nm;, 1A @ 100 pm)

Quantum ? Mechanical Model of Atom

Bohr?s theory considered electron as a particle. This theory does not account for de-Broglie relation and uncertainty principle. The quantum mechanical model of atom is based on the wave ? particle duality and probable distribution of electron.

L.de.Broglie considered that when light behaves like waves and like particles, then electron should also posses dual character i.e., it should behave like material particle and also wave. According to Broglie, the momentum of a particle in motion is inversely proportional to the wavelength of the wave associated with it.

Momentum µ 1_____

Wavelength

P µ 1

or l = h = h

p mv

This equation is known as de Broglie?s equation, where

m= mass of moving particle

v = velocity of particle

h = Planck?s constant

This concept given by Broglie was verified experimentally by Davison and Germer.

Heisenberg Uncertainity Principle

According to this principle, it is not possible to find simultaneously the exact momentum(velocity) of a moving sub-atomic particle. The product of Dx( the uncertainity in position) and Dp (the uncertainity, in momentum) can never be less than

Dx, Dp ³ h

Dp = MDv

Dx. Dv ³ h__

4pm

So, if position of electron is certain its velocity will become uncertain and vice versa. This principle is effective only for motion of sub-atomic particles of very small mass and has no importance for the motion of large objects.

Schrodinger proposed the wave theory to explain behaviour of the electron in the atom and derived an equation known as Schrodinger equation.

¶2 + ¶2 + ¶2

¶x2 ¶y2 ¶z2 Y + 8 p2m (E ? V) Y = 0

where E is total energy, V is potential energy of the electron, Y (wave function) is a function of three co-ordinates x,y and z. The physical significance of the wave funtionY is that the square of this value (Y2) is the measure of the probability of finding the relectron in the atom. Each wave function corresponds to ORBITAL which is the region of space where probability of finding the electron is high.

QUANTUM NUMBERS

The electrons in the atom are identified by three integral numbers called quantum numbers namely principal, azimuthal and magnetic quantum numbers represented by n, l and m respectively. The fourth quantum number(spin)describes, the rotation of electron about its own axis.

Principal Quantum Number (n): It designate the orbit in which elkectron is present, it gives idea of distance of the electron from the nucleus. It has positive integral value except zero. Thus

N= 1,2,3,4 ...etc.

Hence for first orbit n = 1 ; for second orbit n= 2 and so on. The first orbit is ojne nearest the nucleus and has the lowest energy.. Formerly these orbits were described as K,L,M,N...etc., the K bein g the innermost

The maximum number of electrons that can be present in a principal quantum number is 2n2

2, Azimuthal Quantum Number (1): This quantum number describes the shape of electron cloud (orbital) .It also tells that each shell is made up of sub-shell or sub-levels.

L can have integral values from zero to (n- 1 ). Thus for

n = 1 : l = 0 (s sub-shell )

n = 2 . l = 0, 1 (s and p sub-shells respectively)

n = 3 : 1= 0,1,2 (s, p and d sub-shells, respectively)

n = 4 . 1 = 0, 1, 2, 3 (s, p, d and f sub-shells respectively)

Here first shell contain one sub-shell; second shell contains two sub-shells and so on. The sub-shells corresponding to first four values of l (0, l, 2, 3 and 4) are usually denoted by the letters s, p, d, f and g respectively. The maximum number of electrons that can be occupied by a sub-shell is 2 (2l + 1) or 4l + 2.

Designation of Azimuthal Quantum Number (l)by the symbols.

Value of l Designation Shape of sub-shell

0 s spherical

1 p dumb-bell

2 d double dumb-bell

3 f complicated shapes

3, Magnetic Quantum Number (m) :

This quantum number deals with the number of orientations of electrons in a particular orbit under the influence of applied magnetic field. This quantum number explain why there is splitting of spectral lines when the source is placed under the magnetic field (Zeeman's effect). The orientations or the preferred regions of space are called an orbitals. The number of orbital in a sub-shell are given by the values of m.

It may have all integral values between -l to l including zero (-l to zero to + l ). Hence the total number of values of magnetic quantum numbers will be (2l + 1) .

Thus for

1=0: m=O

1=1: m=-1, 0, +1

1=2: m=-2,-1,0,+1 ,+2

1 = 3: m = -3, -2, -1, 0, +1, +2, +3

Hence s- sub-shell will have one;

p -sub-shell will have three

d- sub-shell will have five and

f- sub-shell will have seven possible values of magnetic quantum numbers

The five orbitals in d -sub-shell for which m = -2, -1, 0, + 1 , + 2 are designated as dxy, dyz, dzx, dx2 -y2 of and dz2 respectively.

Spin Quantum Number (5) : This quantum .of number describes the spin of the electron around its own tive axis.

An electron spins around its own axis. This spin creates a small magnetic field. An electron can spin and clockwise or anti-clockwise. Thus s can have two possible values of + ½ or ? 1/2. These values depend upon the direction of the spin. As a rule, when two electrons ,are present in an orbital, these have opposite spins (¯)

S = ± for each value of m spins-clockwise and anticlockwise. Hence two values of this quantum number are possible and for electrons these are + ½ and ?1/2 according to the direction of the spin being clockwise() or anti-clockwise(¯) respectively

Pauli Exclusion Principle

According to this principal, two electrons in a given atom can never have all the values of four quantum numbers identical. For any two electrons, the values of three quantum numbers may be identical bu the value of fourth quantum number must be different. It also suggests that the maximum number of two electrons with opposite spin can be accommodated in an orbital.

Electronic Configurations

Electronic configuration of an atom is the arrangement of electrons in orbits and sub-shells of the atom. It is expressed by indicating the principal quantum number with its representative sub-shell and number of electrons in it is shown by superscript placed on the symbol of sub-shell,

Aufbau Principle.

Aufbau isd Greek word which means building IP. According to this principle, electrons are filled in sub-shells in increasing order of their energies. The increasing order of energy levels is determined by (n + l) rule. According to this principle a new electron will enter into the sub-shell for which the value of (n + l) is minimum. In case the value of(n + l) is same in two or more cases, the new electron enter into that shell for which the value of n is minimum. For example, according to this principle the order of filling of 6p;5s;6s;5p and 4d sub-shells.

Orbital 6p 5s 6s 5p 4d

n + 1 (6 + 1) (5 + 0) (6 + 0) (5 + 1) (4 +2)

=7 =5 =6 =6 =6

will be 5s,4d,5p,6s,6p,(4d,5p,6s)have the same value of (n + l).

The following figure shows simple memory aid for remembering the order of increasing energies

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d

7s 7p

Thus the order of filling electrons in various sub-shells is 1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f5d,6p,7s,5f,6d,7p etc.

Hund?s Rule :Electrons prefer to occupy single orbital of same sub-shell rather than getting paired i.e., electron pairing will not take place in the orbitals of identical energy(degenerate orbitals) until each orbital is singly filled. For example up to five electrons in d-sub shell, electrons will be singly filled with parallel spins

^{_{Orbits of the same sub-shell tend to become full filled or half filled with electrons because these configuration have lesser energy and so more stable than other configuration.
Electrons are distributed in various sub-shell and orbitals following Aufbau, Pauli exclusion principle and Hund?s rule. Electronic configurations of some elements is given below.
Zeeman Effect(1896): Zeeman discovered the spectral lines are split up into components when the source emitting lines is placed in a strong magnetic field. This effect after the name of discoverer is called Zeeman effect.
Compton Effect: In 1923 Compton showed the wave length of any monochromatic radiation increases after it is scattered from matter. The scattering of radiation with increased wavelength after striking through matter is called Compton effect.
This increase in wavelength is called Compton shell (dl= l¢ -l)
X-ray of wavelength l struck a sample of graphite an electron was ejected and the X- ray scattered at an angle q, had higher wavelength l¢ .
l¢ > l
This prove that X-rays consisted particles photon with certain energy on striking with graphite an electron of graphite was ejected out- while doing so the energy of incident X-ray decreased, resulting in the increase of wavelength of ejected X-rays
Isotopes:
The atoms of an element which have similar atomic number but different mass numbers are called isotopes.
For eg. , carbon has three isotopes C12, C13 and C14 where only C14 is radioactive.
Isobars:
Atoms of different element, it similar mass number but different atomic number are called Isobars. For eg,
Calcium and Argon are Isobars:
40 40
Argon 18A Calcium 20Ca
Proton s = 18 Protons = 20
Neutrons = 40-18 Neutrons = 40-20
= 22 =20
Electrons = 18 Electrons = 20
40 40 40
Similarly potassium(19 K ) is also an isobar of these. Thererore, 18A , 19K and
40
20Ca are isobars.
Isotones:
Atoms of different elements with similar number of neutrons in the nuclei, are called isotones. 3 4 13 14 14 15 16
Eg., 1H , 2He .6C , and 7N , 6C , 7N and 8O are isotones}}

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UNKNOWN *

Blazing goIITian

Joined: 26 Feb 2007

Posts: 373

17 Apr 2007 08:39:49 IST

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OBJECTIVE 1

1. Canal rays are

(a) fast moving electrons (b)slow moving neutrons ( c)deflected by electric field (d)deflected by magnetic field (e) both ( c) & (d)

2. Bombardment of Beryllium by alpha particles by alpha particles led to the discovery of

(a)electrons (b)protons ( c)neutrons (d)nucleus (e)positrons

3. The most important defect of Rutherfords model of atom is that

(a)it does not mention about the nucleus of atom

(b)it does not mention about the equivalence of centrifugal force of revolving electron and the attractive e force of revolving electron

( c)it does not obey the Maxwell law of electrodynamics

(d)it does not explain the atomic spectra (e) both ( c) & (d)

4. Atomic mass of an element is not necessarily whole number because

(a)it contains electrons, protons and neutrons

(b)it contains allotropic form ( c)atoms are divisible

(d)it contains isotopes (e)it exhibits isomerism

5. The Introduction of neutron into the nucleus

(a)the no. of electron in the atom (b)the chemical nature ( c) its atomic mass

(d)its atomic number (e)both its atomic mass and atomic number

6. One of the important assumption of Bohr theory is that

(a)the centrifugal force mv² = the attractive force exerted by the nucleus Ze2

r r2

(b)the angular momentum mvr = nh

( c) an electron can take up elliptical orbit besides circular orbits

an electron in an excited state can radiate energy continuously

a positively charged nucleus surrounded by moving electrons In closed orbit

7. Which among the following transitions will give Balmer series in the hydrogen spectrum?

(a) K to L (b)L to M,N, etc ( c)M,N,O etc to L

(d)L,M,N etc to K (e) N,O, etc to M

8. Which of the following has non spherical shell of valence electrons

(a)He (b)B ( c)Be (d)Li (e)H₂

9. The fact that the 3d level has a tendency to remain either half filled or completely filled is illustrated by the electronic configuration of

(a) V and Cr (b)Fe and Co ( c)Co and Ni (d)Cr and Cu (e)Co and V

10. Which of the following configuration is not permissible in the ground state.

(a)3d5 4s1 (b)3d5 4s2 ( c)3d6 4s2 (d)3d7 4s2 (e)3d6 4s1

11. Assuming the velocity to be same which of the following is associated with smallest de- Broglie wavelength

(a) an electron (b) a proton ( c)a neutron

(d)an alpha particle (e) all will have same value of wave length

If the azimuthal quantum number of an electron whose n= 5 and l = 4 is

(a)0 to 1 (b)0 to (l + 1) ( c)-l to +l (d)-l through 0 to +l (e) (l-1) to (l + 1)

13. The filling of the 4p orbital begins in the element of atomic number

(a) 19 (b)29 ( c)31 (d)35 (e)33

14. The first use of quantum theory to explain the structure of atom was made by

(a)Heisenberg (b)Bohr ( c)Planck (d)Einstein (e)de-broglie

15. Which of the following has more unpaired d - electron

(a)Zn+ (b)C02+ ( c)Fe3+ (d)Mn4+ (e)Ni2+

UNKNOWN *

Blazing goIITian

Joined: 26 Feb 2007

Posts: 373

17 Apr 2007 08:41:43 IST

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OBJECTIVE 2

1. Scattering of alpha particles by thin metal foils led to the discovery of

(a)electrons (b) protons ( c)both (a) & (b) (d)neutrons (e)nucleus

2. One of the most important assumption of Rutherfords model of atom is

(a)The centrifugal force mv² = the attractive force exerted by the nucleus Ze2

r r2

(b) the angular momentum mvr = nh

( c) an electron can take up elliptical orbits besides circular orbits

(d) mass and energy are related

(e) the point of impact with matter can be precisely circular orbits

3. The relative abundance of naturally occurring element M s 75 % M 35 25% M37 . The atomic weight of M is

(a)37 (b)35 ( c)36 (d)35.5 (e)38

4. An isotone of 1 H3 is

(a)_{1 H1 (b)1H2 ( c)2He4 (d)2He3 (e)all}

5. An increasing order for the values of e/m for electron (e), proton(p),neutron(n) and alpha particle (a) is

(a)e, p, n a (b)n, p, e, a ( c)n, p,a,e (d)n, a, p, e (e)p, e,a,n

6. The difference between the successive energy levels in an atom(as n value increase)

(a)increases (b)decreases ( c)remains constant (d)has no definite order

7. Which of the following electronic transition in hydrogen atom will require the largest amount of energy.

(a)from n = 1 to n = 2 (b)from n = 2 to n = 3 ( c)from n = ¥ to n = 1

(d) from n= 3 to n = 4 (e)from n =4 to n = 5

8. The energy of an electron in second Bohr orbit of hydrogen atom is ? E. The energy of electron in the first Bohr orbit of the same atom would be.

(a)-2E (b)-2E ( c)-4E (d)-5E (e)-6E

9. Bohr model of atom cannot explain

(a)Zeeman effect (b) Stark effect ( c)fine spectrum (d)all of these (e)none of these

10. The electrons of the same orbital can be distinguished by

(a)principal quantum number (b)azimuthal quantum number

( c)magnetic quantum number (d)spin quantum number (e)elliptical

11. Aufbau principle does not include

(a) (n + 1) rule (b)Octet rule ( c)Hunds rule

(d)Paul?s exclusion principle (e) all of these

12. The following ions/ atoms have five electrons in the outermost orbit, the one which has not the value of 1 azimuthal quantum number equal to 2 is

(a)P(0) (b) Fe(II) ( c)Cr(III) (d)Mn(II) (e)Cu(II)

13. The total energy of the electron in an atom is

(a)a zero under normal conditions of temperature and pressure because electron is very small and of negligible mass

(b) greater than zero and is insgnifcant

( c)May be less or more than zero depending upon the nature of orbital involved

(d)always positive (e)less than zero

14. Which of the following species has more number of electron in comparison with the neutrons?

(a)Al3+ (b)O2- ( c)I2- (d) C (e)Cl-

Bracket series is produced when electron from the outer orbits jumps to

(a)2 nd orbit (b)3 rd orbit ( c)4 th orbit (d)5th orbit (e) Ist orbit

UNKNOWN *

Blazing goIITian

Joined: 26 Feb 2007

Posts: 373

17 Apr 2007 08:42:30 IST

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OBJECTIVE 3

1. Magnetic quantum number specifies:

(a)Size of orbitals (b) shape of orbitals

( c)Orientation of orbitals in space (d)Nuclear stability

2. Which configuration represent a noble gas:

(a)1s^{2 2s2 2p6 3s2 (b)1s2 2s2 2p6 3s2 3p4}

( c) 1s2 2s2 2p6 (d)1s2 2s2 2p6 3s2 3p6 4s2

3. Compared to mass of lightest nucleus the mass of an electron is only:

(a) 1/80 (b)1/360 ( c)1/1800 (d)1/1000

4. For azimuthal quantum number l = 3, the maximum number of electrons will be

(a)2 (b)6 ( c)Zero (d)14.

5. In an atom no two electrons can have the same value for all the quantum numbers. This was proposed by :

(a) Hund (b)Pauli ( c)Dalton (d)Avogadro

6. The mass of a neutron is of the order of

(a)10 ?23 kg (b)10-24 ( c)10-26 (d)10-27 kg

7 The maximum sum of the number of neutrons and protons in an isotope of hydrogen is :

(a)6 (b)5 ( c)4 (d)3

8. Which principle /rule limits the maximum number of electrons in an orbital to two

(a)Aufbau principle (b)Pauli?s exclusion principle

( c)Hund?s rule of maximum multliplicity (d)Heisenberg uncertainty principle

9. The size of nucleus is measured in :

(a)Fermi (b)Angstrom ( c)cm (d)All

10. Which statement does not form part of Bohr?s model of the hydrogen atom.

(a)Energy of the electrons in the orbit is quantized

(b)The electron in the orbit nearest the nucleus is in the lowest energy.

( c)Electrons revolve in different orbits around the nucleus

(d)The position and velocity of the electrons in the orbit cannot be determined simultaneously

11. The principle which gives a way to fill the electrons in the available energy level is:

(a)Hund?s rule (b) Pauli exclusion principle

( c) Aufbau principle (d) None of these

12. In a set of degenerate orbitals, the electrons distribute themselves to have like spins as far as possible. This statement is known as :

(a)Pauli exclusion principle (b)Aufbau principlw

( c)Hund?s rule (d)Slater rules

13. A strong argument for the particle nature of cathode rays is that they

(a) Produce fluorescence (b)Travel through vacuum

( c)Get deflected by electric and magnetic fields (d)Cast shadow

14. The specific charge for positive rays is much less than the specific charge for cathode rays. This is because:

(a)Positive rays are positively charged. (b)Charge on positive rays is less

( c)Positive rays comprise ionized atoms whose mass is much higher

(d)Experimental method for determination is wrong

15. Cathode rays can be deflected by:

(a)Magnetic field only (b)Electric field only ( c) Both types of fields (d) None

16. Photoelectric effect is the phenomenon in which:

(a)Photons come out of a metal when it is hit by a beam of electrons

(b)Photons come out of the nucleus of an atom under the action of an electric field

( c)Electrons come out of a metal with a constant velocity which depends on the frequency and intensity of incident light wave

(d) Electrons come out of a metal with different velocities not greater than a certain value which depends only on the frequency of the incident light wave and not on

its intensity.

17. In photoelectric effect, the photo-current:

(a)Increases with increase of frequency of incident phton

(b)Decreases with increase of frequency of incident photon

( c)Does not depend on the frequency of photon but depends only on the intensity of

incident light

(d)Depends both on intensity and frequency of the incident photon

18. In photoelectric effect the number of photoelectrons emitted is propotional to :

(a)Intensity of incident beam (b)Frequency of incident beam

( c)Velocity of incident beam (d)Work function of photo cathode.

19. According to Bohr?s model of the hydrogen atom, the radius of a stationary orbit

cahracterised by the principle quantum number n is proportional to :

(a) n-1 (b)n ( c)n-2 (d)n2

20. According to Bohr?s theory the radius of electron in an orbit described by principal quantum number n and atomic number Z is proportional to :

(a)Z2n2 (b)Z2/n2 ( c)Z2/n (d)n2/Z

21. The angular momentum of electron in nth orbit is given by :

(a)nh (b)h/2pn ( c)nh/2p (d)n2h/2p

22. Bragg?s equation will have no solution if:

(a)l >2d (b) l < 2d ( c) l <d (d) l = d

23. If l1 and l2 are the wavelength of characteristic X-ray and gamma rays respectively,

then the relation between them is :

(a) l_{1 = 1/l2 (b) l1 = l2 ( c) l1 >l2 (d) l1 < l2}

24. X ? rays do not show the phenomenon of :

(a)Diffraction (b)Polarisation

( c)Deflection by electric field (d)Interference

25. X ? rays and g - rays of same energies may be distinguished by :

(a)Velocity (b)Ionising power ( c)Intensity (d)Method of production.

26. Electronic configuration of H ? is :

(a)1s0 (b)1s1 ( c)1s2 (d)1s1 2s2

27. A p ? orbital can accommodate:

(a)4 electrons (b)6 electrons

( c)2 electrons with parallel spins (d)2 electrons with opposite spins

28. The principle quantum number of an atom represents.

(a)Size of the orbit (b)Spin angular momentum

( c)Orbital angular momentum (d)Space orientation of the orbital

29. If h is Plancks constant, the momentum of a phton of wavelength 0.01 A is :

(a)10-2h (b)h ( c)102h (d)1012h

30. The momentum of a photon is p. The corresponding wavelength is

(a)h/p (b)hp ( c)h/cl (d)h/l

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