Chemistry NCERT Exemplar Solutions Class 11th Chapter Two

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Ans: The mass number (A) is defined as the sum of the number of protons and neutrons present in the nucleus and the atomic number is defined as the number of protons or electrons present in an atom. Thus A=13, the number of neutrons is 7 so the number of protons is 6. Thus, the atomic number is 6.

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Ans: The charged particles get deflected by the electric field. As among the given option only neutron is the particle that is neutral thus it does not get deflected by the electric field.

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Ans: The number of radial nodes is given by n-l-1, where n is principal quantum number, l is azimuthal quantum number. The number of angular nodes is given by n-l, where n is principal quantum number, l is azimuthal quantum number. Here n =3 and l =1 Thus, angular nodes = 3-1 = 2 and radial node = 3-1-1 = 1.

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Ans: In a multielectron atomic system the energy of an electron depends not only on its principal quantum number (shell), but also on its azimuthal quantum number (subshell). Electrons having the same shells and same subshells have the same energy and they are known as degenerate orbitals.

Thus 3d_xy ,3dz² , 3d_yz and 4d_xy, 4d_yz, 4dz² are degenerate.

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Ans: The electronic configuration of nickel is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ 4s² , thus it loses electrons from its 4s orbital as its energy is higher compared to the other orbital.

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Ans: The electronic configuration of oxygen atom is 1s² 2s2 2p⁴ and its orbital diagram is given by

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Ans: The effective nuclear charge (Z_eff) is defined as the net positive charge experienced by the outermost electrons in the atom. With the increase of Azimuthal quantum number (l) the Z_eff experienced by the electron decreases. Hence the arrangement of subshells in the increasing order of Z_eff is : d

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Ans: The drawbacks of Bohr's model were

(i) It was unable to explain the spectra for multi-electron systems

(ii) It could not explain the molecule formation through chemical bonds. The two important developments that contributed significantly towards the change of concept of movement of an electron in an orbit was replaced by, the concept of probability of finding an electron in an orbital were

(i) Dual nature of matter

(ii) Uncertainty Principle. Quantum mechanical model of the atom is the name of the new model.

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Ans: We have

v= 109677 [1/n_i ² - 1/n_f ² ]

Given, n_i = 3 and n_f =2

D E= hcv = 109677 [1/n_i ² - 1/n_f ² ]

DE = - 3.052 * 10^-19J

n =DE /h= 4.606 * 10¹⁶Hz