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Chapter 5 Atomic Structure Chemistry 11th Class Punjab Short Questions

Question No. 1 - State Pauli's exclusion principle and Hund's rule?

Answer No. 1 - According to Pauli's principle "no two electrons in an atom can have the same set of four quantum numbers". According to Hund's rule,"if degenerate orbitals are available and more than two electrons are to be placed in them, then place them in separate orbitals with the same spins rather than in the same orbital with the opposite spins."

Question No. 2 - How the value of the Redberg's constant can be justified from Bohr's equation?

Answer No. 2 -

Question No. 3 - How does Bohr introduce the Planck's quantum theory in his model?

Answer No. 3 - Bohr proposed that electrons move around the nucleus in the fixed orbits with definite energies. Whenever, they change the orbits they emit or absorb the energy in terms of photons which was suggested by Planck.

Question No. 4 - How do you prove that the energy associated with the electron which is revolving around the nucleus of H-atom is negative?

Answer No. 4 -

Question No. 5 - The magnetic quantum number gives us the orientation of orbital in space. Justify it.

Answer No. 5 - In order to designate the directions of p-orbitals in p-subshell, we need an additional quantum number and that is called magnetic quantum number. It tells us the orientation of orbital in space p-subshell has three orbital and thus have three directions in space. For each direction there is a separate value of magnetic quantum number.

Question No. 6 - Why the photographic plate is white and few dark lines are there in the line absorption spectra of a substance?

Answer No. 6 - Some of the photons are absorbed by the sample to excite the electrons of and substance from lower energy levels to higher energy levels. These photons of light don't reach the photographic plate. Rest of the light reaches the photographic plate, arid the plate is white. Only those places are dark in the form of sharp lines where the photon don't reach.

Question No. 7 - What is Zeeman effect?

Answer No. 7 - When the light of spectral lines is passed through the magnetic field, then the one spectra line is splitted up into many spectra lines. This splitting of the spectral line cannot be explained by Bohr's theory.

Question No. 8 - How did Rutherford's model of an atom first of all proved the existence of nucleus of the atom?

Answer No. 8 - Rutherford observed that most of the a-particles passed straight through the gold foil without any deflection from the path. Few of them were deflected at some angle more than 90° and a few were deflected back on the original path. He concluded that the atom contains heavy and positively charged part at the center. This heavy part at the center is called nucleus.

Question No. 9 - According to Bohr's model, the angular momentum of moving electron is a quantize. Justify it.

Answer No. 9 -

Question No. 10 - What is the function of principal quantum number?

Answer No. 10 - Its values are whole numbers and never zero, negative or fractional. It gives us information about:

(i) Energy of electron.

(ii) Distance of electron from the nucleus.

Question No. 11 - How the energy of the plioton can be calculated from the measurement of the frequency, wavelength or wave number of the photon?

Answer No. 11 -

Question No. 12 - How do you come to know that the velocities of electrons in higher orbits are less than those in lower orbits of hydrogen atom?

Answer No. 12 -

Question No. 13 - Energy of an electron is inversely proportional to but energy of higher orbits are always greater than those of the lower orbits. Why?

Answer No. 13 -

Question No. 14 - The energy difference between adjacent levels goes on decreasing sharply. Why?

Answer No. 14 -

Question No. 15 - How the slow neutrons prove to be more effective than the fast neutrons?

Answer No. 15 -

Question No. 16 - Why every series of H-spectrum is a convergent series?

Answer No. 16 - The lines of the every series of H-spectrum are not equally spaced. The reason is that energy levels are not equally spaced. Energy levels become close to each other from lower to the higher levels. For this reason, the lines start coming close to each other. The non-equivalent energy differences make the convergent series.

Question No. 17 - What are defects of Bohr's atomic model?

Answer No. 17 -

Question No. 18 - Heisenberg's uncertainty principle has no relation with Bohr's atomic model. Justify it.

Answer No. 18 - Since the electron has wavy nature and paths are elliptical as well, so the simultaneous determination of position and momentum is not possible. But Bohr's model does not accommodate the wavy nature of electron. He says that the paths are fixed orbits and their orbits are planar. It means that Bohr's model is very simple as compared to Heisenberg's uncertainty principle.

Question No. 19 - The x-rays produced in a discharge tube experiment are characteristic of the target metal. Justify it.

Answer No. 19 - The x-rays which are emitted from the surface of the metal depend upon the atomic number of the metal. Greater the number of protons in the nucleus of metal atom great the forces of attractions for the Inner electrons. Greater the energy differences, smaller the wavelength of x-rays.

Question No. 20 - Why the anode rays depend upon the nature of the gas?

Answer No. 20 - Anode rays are those particles which are consisted of rest of the atom or molecule after the removal of one electron, the mass of every anode ray particle depends upon the nature of the gas, so the anode rays for all gaseous substances are different.

Question No. 21 - Whichever gas is used in the discharge tube, the nature of the cathode rays remains the same. Why?

Answer No. 21 - All the gases are consisted of atoms or molecules. They have electrons in outermost orbitals. These electrons are detached by the high voltage and due to collisions, these electrons become free. They are repelled by the cathode and attracted towards the anode. That is why, they are called cathode rays. They are always electrons and nothing else.

Chapter 5 Atomic Structure Chemistry 11th Class Punjab Short Questions

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