Chemistry Class 11 NCERT Solutions: Chapter 2 Structure of Atom Part 19

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Q: 59. If the velocity of the electron in Bohr’s first orbit is calculate the de Broglie wavelength associated with it.


According to de Broglie’s equation,


h = Planck’s constant

m = mass of electron

v =velocity of electron

Substituting the values in the expression of

Q: 60. The velocity associated with a proton moving in a potential difference of 1000 V is If the hockey ball of mass is moving with this velocity, calculate the wavelength associated with this velocity.


According to de Broglie’s expression,

Substituting the values in the expression,

Q: 61. If the position of the electron is measured within as accuracy of nm, calculate the uncertainty in the momentum of the electron. Suppose the momentum of the electron is is there any problem in defining this value.


From Heisenberg’s uncertainty principle,

Actual momentum

Since the magnitude of the actual momentum is smaller than the uncertainty, the value cannot be defined.

Q: 62. The quantum numbers of six electrons are given below. Arrange them in order of increasing energies. If any of these combination(s) has/have the same energy lists:


For the orbital occupied is 4d.

For the orbital occupied is 3d.

For the orbital occupied is 4p.

Hence, the six electrons i.e., 1, 2, 3, 4, 5, and 6 are present in the 4d, 3d, 4p, 3d, 3p, and 4p orbitals respectively.

Therefore, the increasing order of energies is 5(3p) < 2(3d) = 4(3d) < 3(4p) = 6(4p) < 1(4d).

Q: 63. The bromine atom possesses 35 electrons. It contains electrons in porbital, 6 electrons in 3porbital and 5 electrons in 4porbital. Which of these electron experiences the lowest effective nuclear charge?


Nuclear charge experienced by an electron (present in a multi- electron atom) is dependent upon the distance between the nucleus and orbital, in which the electron is present. As the distance increases, the effective nuclear charge also decreases.

Among p-orbitals, 4p orbitals are farthest from the nucleus of bromine atom with (+35) charge. Hence, the electrons in the 4p orbital will experience the lowest effective nuclear charge. These electrons are shielded by electrons present in the 2pand 3p orbitals along with the s-orbitals. Therefore, they will experience the lowest nuclear charge.