#### Topics

1. How many  total electrons are present in nitrate ion ?
No. of electrons in NO-3 ion = NO of electrons of N+.  NO of electrons  on 3 oxygen atoms + one e -
= 7 + ( 3 + 8 ) + 1  = 32 electrons.

2. What is the lowest value of n that allows g orbits to exist ?
For n the values of l are 0, 1  ...... ( n - 1 )
For n = 5, the value of  l are 0, 1, 2, 3, 4
For l = 4 > g sub - shell can exist. Hence lowest value of n = 5.

3. What are nucleons ?
The neutrons and protons present in the nucleus  of an atom collectively called nucleons.

4. Write electronic configurations of Chromium ( At.  No. = 24)?
Cr = 24 = 1s2, 2s2 2p6, 3s2 3p6 3d5, 4s1

5. Which of the following has smallest de - Broglie wavelength : O2 H2 proton, an electron ?
According to de - Broglie equation     for same value of  velocity
∴O2  molecule has shortest wavelength.

6.  ( i ) An atomic orbital has n = 3.  What are possible values of l and ml ?
(ii) List the quantum numbers ( m1 and l )  of electrons for 3d orbital.
( iii) which of the following orbitals are possible : 1p, 2s, 2p and 3f.
(i )  l     ml
0     0
1    -1, 0, + 1
2    -2, -1, 0 + 1, + 2
( ii ) For 3d orbital  l = 2
The values of m, are -2, -1, 0, +1, +2
(iii) Out of 1p, 2s, 2p  and 3f only 2s, 2p are possible
7. What is the maximum  number of electrons in an atom having n = 3, l = 1 and s = + 1/2
Three electrons ( one each in 3px, 3py, 3pz ).

8. State two properties and examples of electromagnetic radiation?
Electromagnetic radiation show phenomenon of : ( i )  Interference, ( ii )  Diffraction, Examples are : y - rays, x = rays, visible rays  radio waves etc.

9. What is mean by quantisation of electron energy ?
It means that electron in an atom has a certain, specific, discrete amount of energy.

10. Out of 4s and 3d orbitals, which will have higher energy and why ?
3d orbital has higher energy as it has a higher value of ( n + 1 ).

11. What is the difference between a quantum and a photon?
The smallest packet of energy  of any radiation is called a quantum .  Whereas that of light is called a photon.

12. Which  quantum number does not follow from the solution of schrodinger wave equation ?
Spin quantum number.

13.  Describe the important properties of cathode - rays.  What  is concluded about the nature of these rays ?
The cathode rays possess  the  following properties:

( i ) Travel in straight lines perpendicular to surface of cathode.
(ii ) Consists of material particles.
( iii ) Have  got heating effect.
(iv) Consists on negatively charged particles
(v) Produce X - rays when they strike against hard metals like copper, tungsten, platinum etc.
(vi) Produce fluorescence when they strike glass or certain other materials like zinc sulphide.
(vii) Penetrate through  thin  aluminium foils  and other metals.
( viii) Affect the  Photographic plats.
The ratio of charge to mass i.e. charge/ mass is same for all cathode - rays  irrespective of gas used in the tube.  All these properties led to the conclusion that cathode - rays consists of negatively charged fast moving particles.  These particles were named as 'electrons'.

14. which type of ‘Atomic model’ was presented by Rutherford ?Describe in brief?
The  existence of positively charged nucleus  at the centre of atom was first  suggested Rutherford in 1911 on the basis of his interpretation of observation made on scattering experiment.  The main feature of  this model are:
(i ) Atom is spherical and consists of two parts: Nucleus and extra – nuclear part.

(ii) The entire mass and entire positive charge is concentrated in a very small region at the centre known as nucleus.

(iii) The space surrounding the nucleus  known as extra nuclear  part is negatively charged so an atom as a while is neutral.

( iv ) Most of extra – nuclear part is empty.

(v ) The electrons are not stationary but are  revolving  around nucleus at very high speeds like planet  revolving  around the Sun.

15. Describe the drawback of Rutherford’s model of atom?
Main drawback is  that it could not explain the stability of an atom.  Maxwell has shown  that when electric charge is subjected to acceleration, it emits energy in the form of  radiations.  In  Rutherford’s  model of atom, electrons are orbiting the nucleus and hence the direction of their velocity is constantly changing i.e.,  electrons are accelerating.  This will have lesser  and lesser energy and will  get  closer  and closer to the nucleus until at last it spirals into  the nucleus and thus does not provide a stable model of atom.

16. What is meant by  dual nature of radiation ?
The fact  that light energy is  carried in terms of  packets of energy ( i. e., Photons ) as suggested by Planck's  theory means that light has a particle character. at the same time, the fact that light shown interference and diffraction phenomena means that light has a wave character.  These experimental facts led Einstein to suggest that light has a dual character, i.e.,  It behaves both like a wave and like a particle.

17. Describe the important characteristics of anode or positive rays and its importance in the discovery of proton ?
( i ) The anode rays originate in the region between two electrodes in the discharge tube.
( ii ) These rays are made of material particles.
(iii) These rays are positively charged
( iv )  These rays produce the heat when strike against a surface.
( v ) The magnitude of charge on anode - rays varies from particle to particle depending on the number of electrons lost by an atom or molecule.
( vi) The mass of positive particles which constitute these rays depend upon the nature of gas in the tube.
( vii) The charge/ mass ( e/m ) ratio of anode - rays is not constant  but depends upon the nature of gas in the tube.  The value of e.m is greatest for lightest gas hydrogen.  The electric charge on a lightest  positively charged particle from hydrogen gas was found  to be exactly equal in magnitude  but opposite in sign to that  of electron.   This  lightest positively charged particle from hydrogen gas was named as proton.  The mass of proton is almost 1836 times that of electron.

18, What are the shortcomings of Bohr's atomic model?
(i ) It couldn't  explain the spectra of multi - electron atoms.
( ii ) It fails to explain the splitting of spectral lines when subjected to electrostatic or magnetic field ( Stark of Zeeman's effect ).
(iii) it does  not account for the fine  splitting of spectral lines.
( iv ) It affords  a two dimensional picture of revolution of electron while actually electron revolves around  the nucleus in three dimensions.
( v ) It does not account for the shapes of molecules.
According to it, this is possible to determine simultaneously both the position and momentum of the electron   accurately.  But this contrary to Heisenberg's Uncertainty Principle.

19. How it can be proved that the universal constituent of all matter are  'electrons'?
The  charge/ mass  ( e/m) ratio for the particle sin the cathode rays ( i.e., electron ) is found to be same irrespective of nature of cathode or the nature of the gas taken in the discharge tube.  This shows that electrons are universal constitution of all matter.

20. Distinguish between  an Emission  spectrum and an Absorption spectrum?

 Emission Spectrum Absorption Spectrum 1. Emission spectrum is obtained when radiations emitted by the excited substance are analysed in a spectroscope 2. Emission spectrum consists of bright coloured lines separated by dark spaces. 1. Absorption spectrum is  obtained when the whitelight is first passed  through the substance  ( in gaseous state or in solution )  and the  transmitted   light is analysed in a spectroscope.  2. Absorption spectrum consists of dark lines in an otherwise continuous spectrum.
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