Ncert solutions for class 11 chemistry STRUCTURE OF ATOM

1. (i) Calculate the number of electrons which will together weigh one gram.(ii) Calculate the mass and charge of one mole of electrons. 
2. (i) Calculate the total number of electrons present in one mole of methane.(ii) Find (a) the total number and (b) the total mass of neutrons in 7 mg of 14C.(Assume that mass of a neutron = 1.675 × 10–27 kg).(iii) Find (a) the total number and (b) the total mass of protons in 34 mg of NH3 atSTP.Will the answer change if the temperature and pressure are changed ?

3. How many neutrons and protons are there in the following nuclei ?13 16 246 8 12 C, O, Mg,

4.  Write the complete symbol for the atom with the given atomic number (Z) andatomic mass (A)(i) Z = 17 , A = 35.(ii) Z = 92 , A = 233.(iii) Z = 4 , A = 9.

5.  Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculatethe frequency (ν) and wavenumber ( ν ) of the yellow light.

6. Find energy of each of the photons which(i) correspond to light of frequency 3×1015 Hz.(ii) have wavelength of 0.50 Å.

7. Calculate the wavelength, frequency and wavenumber of a light wave whose periodis 2.0 × 10–10 s.

8.  What is the number of photons of light with a wavelength of 4000 pm that provide1J of energy?

9.  A photon of wavelength 4 × 10–7 m strikes on metal surface, the work function ofthe metal being 2.13 eV. Calculate (i) the energy of the photon (eV), (ii) the kineticenergy of the emission, and (iii) the velocity of the photoelectron(1 eV= 1.6020 × 10–19 J).

10. Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise thesodium atom. Calculate the ionisation energy of sodium in kJ mol–1.

11. A 25 watt bulb emits monochromatic yellow light of wavelength of 0.57μm.Calculate the rate of emission of quanta per second.

12. Electrons are emitted with zero velocity from a metal surface when it is exposed toradiation of wavelength 6800 Å. Calculate threshold frequency (ν0 ) and work function(W0 ) of the metal.

13. What is the wavelength of light emitted when the electron in a hydrogen atomundergoes transition from an energy level with n = 4 to an energy level with n = 2?

14. How much energy is required to ionise a H atom if the electron occupies n = 5orbit? Compare your answer with the ionization enthalpy of H atom ( energy requiredto remove the electron from n =1 orbit).

15. What is the maximum number of emission lines when the excited electron of a Hatom in n = 6 drops to the ground state?

16. (i) The energy associated with the first orbit in the hydrogen atom is–2.18 × 10–18 J atom–1. What is the energy associated with the fifth orbit?(ii) Calculate the radius of Bohr’s fifth orbit for hydrogen atom.

17. Calculate the wavenumber for the longest wavelength transition in the Balmerseries of atomic hydrogen.

18. What is the energy in joules, required to shift the electron of the hydrogen atomfrom the first Bohr orbit to the fifth Bohr orbit and what is the wavelength of thelight emitted when the electron returns to the ground state? The ground stateelectron energy is –2.18 × 10–11 ergs.

19. The electron energy in hydrogen atom is given by En = (–2.18 × 10–18 )/n2 J. Calculatethe energy required to remove an electron completely from the n = 2 orbit. What isthe longest wavelength of light in cm that can be used to cause this transition?

20. Calculate the wavelength of an electron moving with a velocity of 2.05 × 107 m s–1.

21. The mass of an electron is 9.1 × 10–31 kg. If its K.E. is 3.0 × 10–25 J, calculate itswavelength.

22. Which of the following are isoelectronic species i.e., those having the same numberof electrons?Na+, K+, Mg2+, Ca2+, S2–, Ar.

23. (i) Write the electronic configurations of the following ions: (a) H– (b) Na+ (c) O2–(d) F–(ii) What are the atomic numbers of elements whose outermost electrons arerepresented by (a) 3s1 (b) 2p3 and (c) 3p5 ?(iii) Which atoms are indicated by the following configurations ?(a) [He] 2s1 (b) [Ne] 3s2 3p3 (c) [Ar] 4s2 3d1.

24. What is the lowest value of n that allows g orbitals to exist?

25. An electron is in one of the 3d orbitals. Give the possible values of n, l and ml for this electron.

26. An atom of an element contains 29 electrons and 35 neutrons. Deduce (i) thenumber of protons and (ii) the electronic configuration of the element.

27. Give the number of electrons in the species H H andO 2 2 2+ , +

28. (i) An atomic orbital has n = 3. What are the possible values of l and ml ?(ii) List the quantum numbers (ml and l ) of electrons for 3d orbital.(iii) Which of the following orbitals are possible?1p, 2s, 2p and 3f

29. Using s, p, d notations, describe the orbital with the following quantum numbers.(a) n=1, l=0; (b) n = 3; l=1 (c) n = 4; l =2; (d) n=4; l=3.

30. Explain, giving reasons, which of the following sets of quantum numbers are not possible

31. How many electrons in an atom may have the following quantum numbers?(a) n = 4, ms = – ½ (b) n = 3, l = 0

32. Show that the circumference of the Bohr orbit for the hydrogen atom is an integralmultiple of the de Broglie wavelength associated with the electron revolving aroundthe orbit.

33. What transition in the hydrogen spectrum would have the same wavelength as theBalmer transition n = 4 to n = 2 of He+ spectrum ?

34. Calculate the energy required for the processHe+ (g) He2+ (g) + e–The ionization energy for the H atom in the ground state is 2.18 × 10–18 J atom–1

35. If the diameter of a carbon atom is 0.15 nm, calculate the number of carbon atomswhich can be placed side by side in a straight line across length of scale of length20 cm long.

36. 2 ×108 atoms of carbon are arranged side by side. Calculate the radius of carbonatom if the length of this arrangement is 2.4 cm.

37. The diameter of zinc atom is 2.6 Å.Calculate (a) radius of zinc atom in pm and (b)number of atoms present in a length of 1.6 cm if the zinc atoms are arranged sideby side lengthwise.

38. A certain particle carries 2.5 × 10–16C of static electric charge. Calculate the numberof electrons present in it.

39. In Milikan’s experiment, static electric charge on the oil drops has been obtainedby shining X-rays. If the static electric charge on the oil drop is –1.282 × 10–18C,calculate the number of electrons present on it.

40. In Rutherford’s experiment, generally the thin foil of heavy atoms, like gold, platinumetc. have been used to be bombarded by the α-particles. If the thin foil of lightatoms like aluminium etc. is used, what difference would be observed from theabove results ?

41. Symbols 7935Br and 79Br can be written, whereas symbols 3579 Br and 35Br are notacceptable. Answer briefly.

42. An element with mass number 81 contains 31.7% more neutrons as compared toprotons. Assign the atomic symbol.

43. An ion with mass number 37 possesses one unit of negative charge. If the ionconatins 11.1% more neutrons than the electrons, find the symbol of the ion.

44. An ion with mass number 56 contains 3 units of positive charge and 30.4% moreneutrons than electrons. Assign the symbol to this ion.

45. Arrange the following type of radiations in increasing order of frequency: (a) radiationfrom microwave oven (b) amber light from traffic signal (c) radiation from FM radio(d) cosmic rays from outer space and (e) X-rays.

46. Nitrogen laser produces a radiation at a wavelength of 337.1 nm. If the number ofphotons emitted is 5.6 × 1024, calculate the power of this laser.

47. Neon gas is generally used in the sign boards. If it emits strongly at 616 nm,calculate (a) the frequency of emission, (b) distance traveled by this radiation in30 s (c) energy of quantum and (d) number of quanta present if it produces 2 J ofenergy.

48. In astronomical observations, signals observed from the distant stars are generallyweak. If the photon detector receives a total of 3.15 × 10–18 J from the radiations of600 nm, calculate the number of photons received by the detector.
    

49. Lifetimes of the molecules in the excited states are often measured by using pulsedradiation source of duration nearly in the nano second range. If the radiation sourcehas the duration of 2 ns and the number of photons emitted during the pulsesource is 2.5 × 1015, calculate the energy of the source.
    

50. The longest wavelength doublet absorption transition is observed at 589 and 589.6 nm. Calcualte the frequency of each transition and energy difference between two excited states.
    

51. The work function for caesium atom is 1.9 eV. Calculate (a) the threshold wavelengthand (b) the threshold frequency of the radiation. If the caesium element is irradiatedwith a wavelength 500 nm, calculate the kinetic energy and the velocity of theejected photoelectron.

52. Following results are observed when sodium metal is irradiated with differentwavelengths. Calculate (a) threshold wavelength and, (b) Planck’s constant.λ (nm) 500 450 400v × 10–5 (cm s–1) 2.554.35 5.35
    

53. The ejection of the photoelectron from the silver metal in the photoelectric effectexperiment can be stopped by applying the voltage of 0.35 V when the radiation256.7 nm is used. Calculate the work function for silver metal.
    

54.  If the photon of the wavelength 150 pm strikes an atom and one of tis inner boundelectrons is ejected out with a velocity of 1.5 × 107 m s–1, calculate the energy withwhich it is bound to the nucleus.
    

55. Emission transitions in the Paschen series end at orbit n = 3 and start from orbit nand can be represeted as v = 3.29 × 1015 (Hz) [ 1/32 – 1/n2]Calculate the value of n if the transition is observed at 1285 nm. Find the region ofthe spectrum.

56. Calculate the wavelength for the emission transition if it starts from the orbit havingradius 1.3225 nm and ends at 211.6 pm. Name the series to which this transitionbelongs and the region of the spectrum.
    

57. Dual behaviour of matter proposed by de Broglie led to the discovery of electronmicroscope often used for the highly magnified images of biological molecules andother type of material. If the velocity of the electron in this microscope is 1.6 × 106ms–1, calculate de Broglie wavelength associated with this electron.
    

58. Similar to electron diffraction, neutron diffraction microscope is also used for thedetermination of the structure of molecules. If the wavelength used here is 800 pm,calculate the characteristic velocity associated with the neutron.

59. If the velocity of the electron in Bohr’s first orbit is 2.19 × 106 ms–1, calculate thede Broglie wavelength associated with it.
    

60. The velocity associated with a proton moving in a potential difference of 1000 V is4.37 × 105 ms–1 . If the hockey ball of mass 0.1 kg is moving with this velocity,calcualte the wavelength associated with this velocity.
    

61. If the position of the electron is measured within an accuracy of + 0.002 nm, calculatethe uncertainty in the momentum of the electron. Suppose the momentum of theelectron is h/4πm × 0.05 nm, is there any problem in defining this value.
    

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

63. The bromine atom possesses 35 electrons. It contains 6 electrons in 2p orbital, 6electrons in 3p orbital and 5 electron in 4p orbital. Which of these electronexperiences the lowest effective nuclear charge ?
    

64. Among the following pairs of orbitals which orbital will experience the larger effectivenuclear charge? (i) 2s and 3s, (ii) 4d and 4f, (iii) 3d and 3p.
    

65. The unpaired electrons in Al and Si are present in 3p orbital. Which electrons willexperience more effective nuclear charge from the nucleus ?
    

66. Indicate the number of unpaired electrons in : (a) P, (b) Si, (c) Cr, (d) Fe and (e) Kr.2.67 
67. (a) How many sub-shells are associated with n = 4 ? (b) How many electrons will bepresent in the sub-shells having ms value of –1/2 for n = 4 ?