EXERCISE CHAPTER 02, NBF CHEMISTRY XI

MCQ’S

I a.     All above II (b) Be , because it is poly electron systm III (b) matter contained electrons
IV (b) – Ze2/4π€r V (d) spin quantum number VI (d) 30
VII (d) 662.5 nm VIII (c) IX (d) radius is 0.529 Å
X (a) XI (b)    
  1. a) How does Mosley’s Law help in the production of X-rays?

The mathematical form of Moseley’s law is √v = a (Z – b) Where a and b are constants for a particular metal.

This law states, “The frequency of a spectral line in an X-ray spectrum varies as the square of atomic number of the element emitting it. Thus by proper selection of target material desired X -rays can be produced”.

  1. b) Which quantum number is also called sub-shell quantum number?

Azimuthal quantum number tells about the shape of orbital or sub-shell therefore, it is called sub-shell quantum number. It is denoted by “l”. It has value from 0, 1, 2, 3 … (n – 1). The numbers 0, 1, 2, 3 … corresponds for

various subshells

e.g. 0 stands for s-subshell ,1 stands for p- subshell, 2 stands for d- subshell, 3 stands for f- subshell

  1. c) What is the difference between an orbit and orbital?
ORBIT ORBITAL
It is the circular path on which It is the region in space in which electron revolves around nucleus It is the region in space in which probability of finding electron is maximum (about 95%  )
This term is used in the Bohr’s theory of atomic structure and it is two dimensional This term was coined by quantum mechanical model and it is three dimensional
Number of electrons in an orbit is Each orbital contains maximum given by the formula, 2n2 The orbital contains maximum two electrons

 

  1. d) What is the relationship between?
  2. a) Energy and wavelength

The energy of radiation is inversely proportional to its wavelength

E=hc/λ  Where  E = Energy of radiation   λ = wavelength of any light radiation   h = Planck’s constant = 6.625 x 10-34 Js

  1. b) frequency and wavelength

Frequency is related to wavelength as

c=v/ λ Where or  v=c/ λ

c = velocity of light = 3 x 108 ms-1                                   λ = wavelength of any light radiation

  1. e) What species are formed by the decay of neutron?

Free neutron decays into proton with the emission of electron and neutrino.

  1. f) Hydrogen atom and He+ are mono electronic system, but the size of He+ is much smaller than H, why?

Both, hydrogen atom and He+ ion have one electron in their outermost shell. However the nucleus of He+ has greater positive charge (due to two protons) than that of hydrogen atom (due to one proton). Therefore, nucleus of He+ attracts its electron more powerfully as compared to hydrogen. Hence, size of He becomes smaller than hydrogen.

  1. g) How the wavelength of moving particles is inversely proportional to its momentum?

The wavelength of particles is inversely proportional to its momentum.

λ =h / mv = h/p

Where p = mv = momentum of particle  λ= wavelength of any light radiation h= Planck’s constant = 6.625 x 10-34 Js

  1. h) State Heisenberg’s uncertainty principle.

It is impossible to determine simultaneously and precisely, both position and momentum of a small fast moving particle e.g. electron.

  1. i) Why is 4s orbital lower in energy than 3d orbital?

According to (n+l)rule, the Energy of orbital is determined from the (n+l) value. Lower the (n+l) value lower will be the energy of orbital & vice versa.

Orbital n+ l Value n value  

The energy value of 4s is lower than 3d

4s 4+0 4
3d 3+2 5

 

  1. j) Write electronic configuration of 25Mn2+, 30Zn2+, 24Cd3+, 13Al3+.

 

  1. k) What is (n+ l) rule?

 

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