Important Questions Class 11 Chemistry – Structure of Atom
Important Questions Class 11 Chemistry
Que 1. Calculate the charge of one mole of electrons.
Ans 1. One electron has charge 1.602 × 10−19 coulombs
one mole of electrons has charge = 6.023 × 1023 × 1.602 × 10−19
= 9.648846 × 104 = 96488.5 coulombs
Que 2. Calculate the mass of one mole of electrons.
Ans 2. Mass of electron = 9.1 × 10−31 kg
One mole of electrons has mass = 6.023 × 1023 × 9.1 × 10−31
= 54.8 × 10−8 = 5.48 × 10−7 kg
Que 3. How many p electrons are present in sulphur atom?
Ans 3. Sulphur has an electronic configuration
1s2 2s2 2p6 3s2 3p4
∴ Sulphur has 10 ‘p’ electrons.
Que 4. What are the values of the principal quantum number (n) and azimuthal quantum number (l) for a 3d electron?
Ans 4. For a 3d – electron principal quantum number (n) = 3 and Azimuthal quantum number (l) = 2.
Que 5. What is the completer symbol for the atom with the given atomic number (Z) and atomic mass (A)? i) Z = 4, A= 9 ii) Z = 17, A = 35 iii) Z = 92, A = 233.
Ans 5. i) Z = 4, A = 9 Complete symbol is 4Be9
ii) Z = 17, A = 35 Complete symbol is 17Cl35
iii) Z = 92, A = 233 Complete symbol is 92U233
Que 6. What is the frequency of radiation of wavelength 600 nm?
Ans 6. We know
ν = c/Λ
= 3 × 108/6 × 10-7
= 5 × 1014 s
Que 7. What is the Zeeman effect?
Ans 7. The splitting up of spectral lines in the presence of a strong external magnetic field is called as Zeeman effect.
Que 8. What is the Stark effect?
Ans 8. The splitting of spectral lines in the presence of a strong electric field is called as Stark effect.
Que 9. Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 4000 Ȧ. What is the threshold frequency (v0)?
Ans 9. We know
Important Questions Class 11 Chemistry
Que 10. Which of the following orbitals are possible? 2s,1p,3f,2p.
Ans 10. 2s,2p orbitals are possible among 2s, 1p, 3f, 2p and 1p, 3f orbitals are not possible.
Que 11. How many electrons in an atom may have n = 4 and m = +1/2?
Ans 11. For n = l values are 0,1,2,3
l = → 0 s contains are electron with ms = +1/2
l = → 1 p contains 3 electrons with ms = +1/2
l = → 2 d contains 5 electrons with ms = +1/2
l = → 3 f contains 7 electrons with ms = +1/2
∴ Total no. of electrons with ms = +1/2
for n = 4 = 1 + 3 + 5 + 7 = 16.
Que 12. What is the physical significance of Ψ2?
Ans 12. Ψ2 represents the probability of finding an electron. It is the probability of finding a particle specified by a particular wave function.
Que 13. Which orbital is non-directional?
Ans 13. s- orbital is spherically symmetrical i.e. it is non-directional. It has a spherical shape, like a hollow ball.
Que 14. What is the quantization of energy?
Ans 14. Quantization of energy means the energy is distributed and transmitted in the form of packets. These packets are called photons.
Que 15. Why are spectral lines considered fingerprints?
Ans 15. Identification of the elements can be made from these lines. Just like fingerprints, the spectral lines of no two elements resemble each other.
Que 16. Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.
Ans 16. The electronic arrangement of a helium atom is 1s2 which contains two valence electrons, but because it does not form a chemical bond, its duplet is complete. As a result, valency is zero.
Que 17. Why are 2d and 3f orbitals not possible?
Ans 17. For n = 2, the permitted values of l are 0 and 1. This means the 2nd shell has only s and p orbitals, not d. Similarly, for n = 3, the permissible values are 0, 1, and 2. Thus only s, p, and d orbitals are permitted not f.
Que 18. Out of 3d and 4s orbitals which are filled first?
Ans 18. 4s orbital is filled first because it has lower energy. The energies of the orbitals can be compared by their (n + l) values. For 4s orbital (n + l) i.e. 4 + 0 value is 4 while for 3d orbital, (n + l) i.e. 3 + 2 value is 5, Therefore, 4s orbital is filled before 3d orbital.
Que 19. Calculate the wavelength of the radiation emitted, producing a line in the Lyman series when an electron falls from the fourth stationary state in the hydrogen atom (RH = 1.1 × 107 m–1).
Ans 19. For the Lyman series n1 = 1
Que 20. A moving electron has 5 × 10–25 J of kinetic energy. What is the de-Broglie wavelength?
Ans 20. Mass of the electron m = 9.1 × 10–31 kg
Que 21. Write down the four quantum numbers for the fifth and sixth electrons of the carbon atom.
Ans 21. 6C → 1s2, 2s2, 2p2
fifth electron → n = 2 l = 1 m = – 1 or +1 s = + 1/2 or – 1/2
sixth electron → n = 2 l = 1 m = 0 s = + 1/2 or – ½
Que 22. 23Na is the most stable isotope of Na. Find out the process by which 11Na24 can undergo radioactive decay.
Ans 22. n/p ratio of 24Na is 13/11 and thus greater than one. It will therefore decay following b-emission.
11Na24 → 12Mg24 + 1e0
Que 23. What are the main features of Rutherford’s model of an atom?
Ans 23. Atom is spherical and consists of two parts: Nucleus and an extra-nuclear part.
a) The entire mass and entire positive charge are concentrated in a very small region at the center known as the nucleus.
b) The space surrounding the nucleus known as the extra-nuclear part is negatively charged so an atom as a whole is neutral.
c) Most of the extra-nuclear part is empty.
d) The electrons are not stationary but are revolving around the nucleus at very high speeds like planets revolving around the Sun.
Que 24. What is meant by the dual nature of radiation?
Ans 24. 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 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.
Que 25. Describe the drawback to Rutherford’s model of the atom.
Ans 25. The main drawback is that it could not explain the stability of an atom. Maxwell has shown that when an electric charge is subjected to acceleration, it emits energy in the form of radiation. In Rutherford’s model of the atom, electrons are orbiting the nucleus and hence the direction of their velocity is constantly changing, i.e., electrons are accelerating.
This will cause the electrons 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 the atom.
Important Questions Class 11 Chemistry
Que 26. Arrange s, p, and d sub-shells of a shell in the increasing order of effective nuclear charge (Zeff) experienced by the electron present in them.
Ans 26. The increasing order of effective nuclear charge (Zeff) experienced by the electron present in them is s > p > d because s is close to the nucleus, and it will shield the nuclear charge more effectively.
Que 27. Why Rutherford’s model could not explain the stability of an atom?
Ans 27. According to the electromagnetic theory of Maxwell, when charged particles are accelerated then they should emit electromagnetic radiation. Therefore, an electron in an orbit will continue to emit radiation for infinite time, the orbit will then continue to shrink which is not the case in an atom.
Que 28. What is the meaning of the quantization of energy?
Ans 28. Quantization of energy means the energy of energy levels can have some specific values and not all the values.
Que 29. Out of electrons and protons, which one will have a higher velocity to produce matter waves of the same wavelength? Explain it.
Ans 29. Out of the electron and proton, being the lighter particle, the electron will have the higher velocity and produce matter waves of the same wavelength.
Que 30. What are degenerate orbitals?
Ans 30. Orbitals have the same energy belonging to the same subshell.
Important Questions Class 11 Chemistry
Que 31. Which of the following are isoelectronic species i.e., those having the same number of electrons?
Na+, K+, Mg2+, Ca2+, S2-, Ar.
Ans 31. We know Isoelectronic species are the species having the same number of electrons.
A positive charge means the shortage of an electron.
A negative charge means a gain of electrons.
Number of electrons in Na+ = 11-1 = 10
Number of electrons in K+ = 19-1 = 18
Number of electrons in Mg2+ = 12-2 = 10
Number of electrons in Ca2+ = 20-2 = 18
Number of electrons in S2- = 16+2 = 18
Number of electrons in Ar = 18
Isoelectronic species:
i) Na+ and Mg2+ (10 electrons each)
ii) K+, Ca2+, S2- and Ar (18 electrons each)
Que 32. Which one Fe3+, Fe2+ is more paramagnetic and why?
Ans 32. As Fe3+ contains 5 impaired electrons while Fe2+ contains only 4 unpaired electrons. Fe3+ is more paramagnetic.
Que 33. Calculate the total number of required angular nodes and radial nodes present in the 3p orbital.
Ans 33. Nodes are the region present among the particular orbitals where one can find the probability density of finding electrons would be zero.
In the case of np orbitals, the radial nodes,
= n – l – 1
= 3 –1 – 1 = 1
Angular nodes = l = 1.
Que 34. Distinguish between a photon and a quantum.
Ans 34. A quantum is a bundle of energy of a definite magnitude (E = hv) and it may be from any source. However, a photon is a quantum of energy associated with light only.
Que 35. An atom that has atomic mass number 13 has seven neutrons. What is the atomic number of the given atom?
Ans 35. The mass number of the atom = number of protons + number of neutrons. Hence, the atomic number (number of protons) = mass number – no. of neutrons. The atomic number of the given atom: 13 – 7 = 6.
Que 36. Give the drawbacks of J.J. Thomson’s experiment.
Ans 36. The drawbacks are:
(i) It failed to explain the origin of the spectral lines of hydrogen and other atoms.
(ii) It failed to explain the scattering of α particles in Rutherford’s scattering experiment.
Que 37. Which of the following will not show deflection from the path on passing through an electric field? Proton, cathode rays, electron, neutron.
Ans 37. Neutrons will not deviate from their path when passing through an electric field because they are neutral in nature and thus are unaffected by any electrical field.
Que 38. An electron is in one of the 3d orbitals. Give the possible values of n, l, and ml for this electron.
Ans 38. For the 3d orbital:
Principal quantum number (n) = 3
Azimuthal quantum number (l) = 2
Magnetic quantum number (ml) = -2, -1, 0, 1, 2
Que 39. When is the energy of an electron regarded as zero?
Ans 39. The energy of the electron is regarded as zero when it is at an infinite distance from the nucleus.
At that point force of attraction between the electron and the nucleus is almost nil. Therefore, its energy is regarded as zero.
Que 40. What experimental evidence supports the idea that an atom’s electronic energies are quantized?
Ans 40. The bright-line spectrum shows that the energy level in an atom is quantized. These lines obtained the result of an electronic transition between the energy and if the electronic energy level were continuous and not quantized or discrete; the atomic spectra would have shown a constant absorption (from the lower to higher energy level transition) or emission (from higher to lower energy level transition.
Important Questions Class 11 Chemistry
