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💥MDCAT/ECAT Chemistry Chapter-wise High-Yield Chemistry MCQs on Atomic Structure 🧬| Exam-Focused, 🎯 💯 Exam Booster🚀 Practice & Win 190+! 📚 Topper’s Choice
1. Bohr's theory is NOT applicable to which of the following:
🟩 a) H
🟦 b) H⁺
🟨 c) He⁺
🟥 d) Li²⁺
2. Nitrogen has the configuration 1s² 2s² 2pₓ¹ 2pᵧ¹ 2p𝓏¹ and 1s² 2s² 2pₓ² 2pᵧ¹. This is determined by:
🟩 a) Aufbau principle
🟦 b) Pauli’s rule
🟨 c) Hund’s rule
🟥 d) n + l rule
3. Quantum number values for 3s orbital are:
🟩 a) n = 0, l = 1
🟦 b) n = 1, l = 0
🟨 c) n = 3, l = 1
🟥 d) n = 3, l = 0
4. The radius of first orbit of hydrogen atom is:
🟩 a) 529 Å
🟦 b) 52.9 Å
🟨 c) 5.29 Å
🟥 d) 0.529 Å
5. Line spectrum is used as a tool for the identification of:
🟩 a) Colors
🟦 b) Electrons
🟨 c) Elements
🟥 d) Molecules
6. The shape of orbital for which l = 0 is:
🟩 a) Spherical
🟦 b) Dumbbell
🟨 c) Double dumbbell
🟥 d) Complicated
7. When 4d orbital is filled, the next electron enters into:
🟩 a) 5s
🟦 b) 5p
🟨 c) 5d
🟥 d) 6s
8. Which of the following is NOT an isoelectronic pair?
🟩 a) Na⁺ and Ne
🟦 b) Na⁺ and F⁻
🟨 c) Na and Ca
🟥 d) Na⁺ and Mg²⁺
9. Balmer series appears in the hydrogen spectrum if electron jumps to:
🟩 a) Second orbit
🟦 b) Third orbit
🟨 c) Fourth orbit
🟥 d) Fifth orbit
10. In 1935 A.D. James Chadwick was awarded Nobel Prize because:
🟩 a) He discovered proton
🟦 b) He discovered neutron
🟨 c) He determined radius of hydrogen atom
🟥 d) He gave rules for electronic configuration
11. The fast moving electrons like the cathode rays are called:
🟩 a) Alpha rays
🟦 b) Beta-rays
🟨 c) Gamma rays
🟥 d) Deuterons
12. Cathode rays experiment shows the presence of:
🟩 a) Electrons
🟦 b) Protons
🟨 c) Neutrons
🟥 d) Nucleus
13. The e/m ratio of cathode rays (electrons) is:
🟩 a) 1.7588 × 10¹¹ C/kg
🟦 b) 1.7588 × 10⁸ C/g
🟨 c) Both a and b
🟥 d) None of them
14. The charge on an electron is:
🟩 a) 1.6022 × 10⁻¹⁹ C
🟦 b) 1.6022 × 10⁻¹⁸ C
🟨 c) 1.6022 × 10⁻²⁹ C
🟥 d) 1.6022 × 10⁻²¹ C
15. The mass of an electron is:
🟩 a) 9.1096 × 10⁻¹⁹ kg
🟦 b) 9.1096 × 10⁻³¹ kg
🟨 c) 9.1096 × 10⁻²⁰ kg
🟥 d) 9.1096 × 10⁻³⁰ kg
16. Which particle has a mass of 1/1836 times that of hydrogen?
🟩 a) Electron
🟦 b) Proton
🟨 c) Neutron
🟥 d) Positron
17. The e/m ratio for positive (anode) rays is … of nature of gas used:
🟩 a) Dependent
🟦 b) Independent
🟨 c) None of the above
🟥 d) All of them
18. The phenomenon of emission of radioactive radiations from nuclei of lighter isotopes of a stable element due to bombardment of fast moving subatomic particles is called:
🟩 a) Radioactivity
🟦 b) Natural radioactivity
🟨 c) Artificial radioactivity
🟥 d) Cleavage
19. Which gas has the highest value of e/m ratio?
🟩 a) Hydrogen
🟦 b) Helium
🟨 c) Nitrogen
🟥 d) Oxygen
20. These are helium nuclei with double positive charge and atomic mass of 4 amu:
🟩 a) Alpha rays
🟦 b) Beta-rays
🟨 c) Gamma rays
🟥 d) X-rays
21. Alpha rays consist of:
🟩 a) Stream of Helium
🟦 b) Stream of electron only
🟨 c) Stream of neutron only
🟥 d) Stream of H
22. The phenomenon of radioactivity was discovered by Henry Becquerel in 1896 A.D. while working on uranium mineral called:
🟩 a) Pitch-blende
🟦 b) Zinc sulphide
🟨 c) Fluorspar
🟥 d) Positron
23. Marie Curie and Pierre Curie isolated and separated two new radioactive elements named:
🟩 a) Radium & Polonium
🟦 b) Radium & Radon
🟨 c) Radium & Actinium
🟥 d) None of them
24. Initially nuclear rays were named as:
🟩 a) Becquerel rays
🟦 b) Curie’s rays
🟨 c) Both of them
🟥 d) None of them
25. The ionization power of alpha rays is … times greater than beta rays:
🟩 a) 100
🟦 b) 1000
🟨 c) 10,000
🟥 d) None of them
26. The ionization power of alpha rays is … times greater than gamma rays:
🟩 a) 100
🟦 b) 1000
🟨 c) 10,000
🟥 d) None of them
27. Which isotope is used to measure the age of fossils and artefacts (archaeology)?
🟩 a) Carbon-14
🟦 b) Carbon-12
🟨 c) Iodine-131
🟥 d) None of them
28. Which rays are electromagnetic radiations traveling with velocity of light?
🟩 a) Alpha rays
🟦 b) Beta-rays
🟨 c) Gamma rays
🟥 d) Deuterons
29. The wavelength of gamma rays is … than most of the X-rays:
🟩 a) Shorter
🟦 b) Larger
🟨 c) Equal
🟥 d) All of them
30. Gamma rays are emitted as:
🟩 a) Protons
🟦 b) Electrons
🟨 c) Neutrons
🟥 d) Photons
31. Negatively charged particle nature of cathode rays was first demonstrated in 1895 by:
🟩 a) Millikan
🟦 b) J. J. Thomson
🟨 c) Hittrof
🟥 d) J. Perrin
32. Which radioactive rays have greater penetrating power?
🟩 a) Alpha rays
🟦 b) Beta-rays
🟨 c) Gamma rays
🟥 d) None of them
33. The particle with the highest e/m ratio is:
🟩 a) Proton
🟦 b) Neutron
🟨 c) Electron
🟥 d) Alpha particle
34. Which of the following pairs have identical values of e/m?
🟩 a) A proton and a neutron
🟦 b) A proton and deuterium
🟨 c) Deuterium and an α-particle
🟥 d) An electron and γ-rays
35. Which is not true with respect to cathode rays?
🟩 a) A stream of electrons
🟦 b) Charged particles
🟨 c) Move with speed same as that of light
🟥 d) Can be deflected by magnetic fields
36. Which of the following is the main cause of late discovery of neutron?
🟩 a) Neutron is chargeless particle
🟦 b) Neutron is highly unstable particle
🟨 c) Neutron in the nucleus moves very fast
🟥 d) All of these
37. Emission from Th-231 produces Th-227:
🟩 a) One alpha emission
🟦 b) Four beta emission
🟨 c) Two alpha and two beta emission
🟥 d) One alpha and two beta emission
38. The e/m ratio of positive rays is always:
🟩 a) Much smaller than cathode rays
🟦 b) Much greater than cathode rays
🟨 c) Equal to cathode rays
🟥 d) Unpredictable
39. Alpha particle consists of:
🟩 a) 2 protons and 1 neutron
🟦 b) 2 electrons and 2 neutrons
🟨 c) 2 protons and 2 neutrons
🟥 d) 2 protons and 3 neutrons
40. Which order is correct?
🟩 a) Electron < Proton < Neutron
🟦 b) Proton < Electron < Neutron
🟨 c) Neutron < Electron < Proton
🟥 d) Proton < Neutron < Electron
41. X-rays have same nature as:
🟩 a) Gamma rays
🟦 b) Cathode rays
🟨 c) Alpha rays
🟥 d) Beta rays
42. The frequency of X-rays is:
🟩 a) Very small
🟦 b) Very high
🟨 c) Intermediate
🟥 d) All of them
43. The wavelength of X-rays ranges:
🟩 a) 0.1 to 10 Å
🟦 b) 0.1 to 100 Å
🟨 c) 0.2 to 10 Å
🟥 d) None of them
44. Spectral line of short wavelength of X-rays is called:
🟩 a) K-series
🟦 b) L-series
🟨 c) M-series
🟥 d) None of them
45. In 1913, Henry Moseley studied X-rays produced from anodes of 38 metals from:
🟩 a) Aluminium to Gold
🟦 b) Calcium to Gold
🟨 c) Aluminium to Tin
🟥 d) None of them
46. Spectrum given due to transition of electron from M to L shell is:
🟩 a) Absorption
🟦 b) Emission
🟨 c) Continuous
🟥 d) None of these
47. The square root of frequency is directly proportional to atomic number. This is statement of:
🟩 a) Moseley law
🟦 b) Henry’s law
🟨 c) Hund’s rule
🟥 d) None of them
48. Moseley found that wavelength of X-rays emitted … regularly with increasing atomic number:
🟩 a) Increase
🟦 b) Decrease
🟨 c) Both a and b
🟥 d) None of them
49. An instrument that measures intensity and frequency of emitted or absorbed photon radiation is:
🟩 a) Spectrometer
🟦 b) Hydrometer
🟨 c) Barometer
🟥 d) Calorimeter
50. The energy of photon is inversely proportional to:
🟩 a) Frequency of light
🟦 b) Wavelength
🟨 c) Speed of light
🟥 d) None of them
51. The energy of photon is directly proportional to:
🟩 a) Frequency of light
🟦 b) Wavelength
🟨 c) Both of them
🟥 d) None of them
52. The spectrum of sun or of incandescent solids (electric light) is:
🟩 a) Line spectrum
🟦 b) Continuous spectrum
🟨 c) Both a and b
🟥 d) None of them
53. Light of a single wavelength is called:
🟩 a) Monochromatic
🟦 b) Dichromatic
🟨 c) Polychromatic
🟥 d) All of them
54. It is called fingerprint of element:
🟩 a) Line spectrum
🟦 b) Continuous spectrum
🟨 c) Absorption spectrum
🟥 d) All of them
55. Violet colour has a wavelength of:
🟩 a) 4000–4200 Å ✅
🟦 b) 4200–4600 Å
🟨 c) 4600–5000 Å
🟥 d) None of them
56. The colour with wavelength 600–630 nm (6000–6300 Å) is:
🟩 a) Red
🟦 b) Green
🟨 c) Yellow
🟥 d) Orange
57. 1 Å is equal to:
🟩 a) 10⁻¹⁰ m
🟦 b) 10⁻⁸ cm
🟨 c) 10⁻¹ nm or 10² pm
🟥 d) All of them ✅
58. The value of Planck’s constant is:
🟩 a) 6.625 × 10⁻³⁴ J·s
🟦 b) 6.625 × 10⁻³² J·s
🟨 c) 6.625 × 10⁻³⁶ J·s
🟥 d) 6.625 × 10⁻²⁸ J·s
59. The number of waves per unit distance is called:
🟩 a) Wave frequency
🟦 b) Wavelength
🟨 c) Amplitude
🟥 d) Wave number
60. The photons of which one of the following colours are more energetic than the blue colour?
🟩 a) Indigo
🟦 b) Red
🟨 c) Orange
🟥 d) Yellow
61. Continuous spectrum is the property of matter in:
🟩 a) Gaseous atomic state
🟦 b) Small amount
🟨 c) Bulk
🟥 d) Both a and c
62. The study of absorption or emission of electromagnetic radiation is called:
🟩 a) Electrochemistry
🟦 b) Spectroscopy
🟨 c) Chemical kinetics
🟥 d) Polarimetry
63. Centimeter inverse is the unit of:
🟩 a) Boltzmann constant
🟦 b) Gas constant
🟨 c) Rydberg’s constant
🟥 d) Planck’s constant
64. The spectrum of molecular form of the substance is called:
🟩 a) Band spectrum
🟦 b) Line spectrum
🟨 c) Absorption spectrum
🟥 d) All of them
65. The spectrums having dark spaces are called:
🟩 a) Absorption spectrum
🟦 b) Continuous spectrum
🟨 c) Emission spectrum
🟥 d) Atomic spectrum
66. Line spectrum is produced by:
🟩 a) O₂
🟦 b) H
🟨 c) H₂
🟥 d) N₂
67. Electromagnetic radiations produced from nuclear reactions are:
🟩 a) X-rays
🟦 b) Gamma rays
🟨 c) Beta rays
🟥 d) Alpha rays
68. Greater the wavelength associated with the photon:
🟩 a) Greater is its energy
🟦 b) Smaller is its energy
🟨 c) Its energy will be variable
🟥 d) Its energy will remain constant
69. Greater the wave number of photons:
🟩 a) Greater is its energy
🟦 b) Smaller is its energy
🟨 c) Its energy will be variable
🟥 d) Its energy will remain constant
70. Greater the frequency associated with the photon:
🟩 a) Greater is its energy
🟦 b) Smaller is its energy
🟨 c) Its energy will be variable
🟥 d) Its energy will remain constant
71. Lesser the wave number of photons:
🟩 a) Greater is its energy
🟦 b) Smaller is its energy
🟨 c) Its energy will be variable
🟥 d) Its energy will remain constant
72. The velocity of photon is:
🟩 a) Dependent on its source
🟦 b) Equal to square of its amplitude
🟨 c) Dependent on its wavelength
🟥 d) Independent of its wavelength
73. Photons of red colour are:
🟩 a) More energetic than violet
🟦 b) Less energetic than violet
🟨 c) Equal energetic to violet
🟥 d) None of the above
74. Rutherford’s alpha particle scattering experiment showed for the first time that the atom has:
🟩 a) Electrons
🟦 b) Protons
🟨 c) Neutrons
🟥 d) A nucleus
75. Which nature of electron was explained by Bohr’s theory?
🟩 a) Particle
🟦 b) Wave
🟨 c) Dual
🟥 d) None of them
76. According to Bohr’s atomic model, the angular momentum of orbits is multiple of:
🟩 a) h/2π
🟦 b) 2π/h
🟨 c) 2h/π
🟥 d) π/2h
77. When electrons move from higher energy level to lower energy level, energy is:
🟩 a) Absorbed
🟦 b) Emitted
🟨 c) Both (a) and (b)
🟥 d) None of them
78. The centripetal force required for motion of electron around nucleus is provided by:
🟩 a) Gravitational force
🟦 b) Electrostatic force
🟨 c) Weak nuclear force
🟥 d) Nuclear force
79. Angular momentum of electron in kg·m²/s in 3rd Bohr’s orbit is:
🟩 a) 1.11 × 10⁻³⁴
🟦 b) 2.1 × 10⁻³⁴
🟨 c) 3.1 × 10⁻³⁴
🟥 d) 4.1 × 10⁻³⁴
80. When electron remains between orbits its momentum is:
🟩 a) Emitted
🟦 b) Changed always
🟨 c) Dequantized
🟥 d) Quantized
81. Bohr’s theory does not explain the spectra of:
🟩 a) Hydrogen
🟦 b) Multi-electron system
🟨 c) Single electron system
🟥 d) None of them
82. Bohr’s theory is only applicable to:
🟩 a) Hydrogen
🟦 b) Hydrogenic ion
🟨 c) Both of them
🟥 d) None of them
83. The angular momentum of an electron in the nth orbit is 3.17 × 10⁻³⁴ J·s. What is the value of ‘n’?
🟩 a) n = 1
🟦 b) n = 2
🟨 c) n = 3
🟥 d) n = 4
84. When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by:
🟩 a) h/2π
🟦 b) 2h/2π
🟨 c) 3h/2π
🟥 d) 4h/2π
85. The splitting of spectral line in presence of electric field is called:
🟩 a) Stark effect
🟦 b) Zeeman effect
🟨 c) Photoelectric effect
🟥 d) None of them
86. The splitting of spectral line in presence of magnetic field is called:
🟩 a) Stark effect
🟦 b) Zeeman effect
🟨 c) Photoelectric effect
🟥 d) None of them
87. The numerical value of Bohr’s radius is:
🟩 a) 5.29 × 10⁻¹¹ m
🟦 b) 5.29 × 10⁻⁹ cm
🟨 c) 0.529 Å
🟥 d) All of them
88. According to Bohr’s theory of hydrogen atom, the radii rnr_n of electron orbits are related to n as:
🟩 a) rₙ ∝ 1/n²
🟦 b) rₙ ∝ 1/n
🟨 c) rₙ ∝ n
🟥 d) rₙ ∝ n²
89. Which one of the following is the correct formula for calculating radius of nth orbit?
🟩 a) n²h²εₒ/πmZe² 🟦 b) Z² e⁴m /8 εₒ² n²h²
🟨 c) e⁴m /8 εₒ² h²
🟥 d) None of them
90. The Rydberg constant R in per meter is:
🟩 a) 1.0968 × 10⁹
🟦 b) 1.0968 × 10¹²
🟨 c) 1.0968 × 10¹¹
🟥 d) 1.0968 × 10⁷
91. The radius of the second Bohr’s orbit for hydrogen atom is:
🟩 a) 1.65 Å
🟦 b) 4.76 Å
🟨 c) 0.529 Å
🟥 d) 2.12 Å
92. Correct formula for calculating energy of electron in nth orbit:
🟩 a) n²h²εₒ/πmZe²
🟦 b) Z² e⁴m /8 εₒ² n²h²
🟨 c) e⁴m /8 εₒ² h²
🟥 d) None of them
🟦 b) Z² e⁴m /8 εₒ² n²h²
🟨 c) e⁴m /8 εₒ² h²
🟥 d) None of them
93. Correct formula for calculating energy emitted during electronic transition:
🟩 a) n²h²εₒ/πmZe²
🟦 b) e⁴m /8 εₒ² h³ [1/n₁²–1/n₂²]
🟨 c) e⁴m /8 εₒ² h² [1/n₁²–1/n₂²]
🟥 d) Z² e⁴m /8 εₒ² n²h²
🟦 b) e⁴m /8 εₒ² h³ [1/n₁²–1/n₂²]
🟨 c) e⁴m /8 εₒ² h² [1/n₁²–1/n₂²]
🟥 d) Z² e⁴m /8 εₒ² n²h²
94. Correct formula for calculating frequency emitted during electronic transition:
🟩 a) n²h²εₒ/πmZe²
🟦 b) e⁴m /8 εₒ² h³ [1/n₁² – 1/n₂²]
🟨 c) e⁴m /8 εₒ² h² [1/n₁² – 1/n₂²]
🟥 d) Z² e⁴m /8 εₒ² n²h²
🟦 b) e⁴m /8 εₒ² h³ [1/n₁² – 1/n₂²]
🟨 c) e⁴m /8 εₒ² h² [1/n₁² – 1/n₂²]
🟥 d) Z² e⁴m /8 εₒ² n²h²
95. Correct formula for calculating wave number emitted during electronic transition:
🟩 a) e⁴m /8 εₒ² h³c [1/n₁² – 1/n₂²]🟦 b) e⁴m /8 εₒ² h³ [1/n₁² – 1/n₂²]
🟨 c) e⁴m /8 εₒ² h² [1/n₁² – 1/n₂²]
🟥 d) Z² e⁴m /8 εₒ² n²h²
96. The value of constant ‘K’ in formula for energy of electron in nth orbit is:
🟩 a) 2.18 × 10⁻¹⁸ J/atom
🟦 b) 1312.8 kJ/mol
🟨 c) 13.6 eV
🟥 d) All of them
97. According to Bohr’s atomic model, the radius of the orbit is directly proportional to:
🟩 a) n²
🟦 b) 1/n²
🟨 c) 1/n
🟥 d) n
98. Radius of hydrogen atom in first excited state is ____ of Bohr’s radius:
🟩 a) Double (Twice)
🟦 b) Half
🟨 c) 4 times
🟥 d) Same
99. Order of the radius of an electron orbit in hydrogen atom:
🟩 a) 10⁻⁸ m
🟦 b) 10⁻⁹ m
🟨 c) 10⁻¹¹ m
🟥 d) 10⁻¹³ m
100. Hydrogen atoms excited from ground state to n = 4. Number of spectral lines observed:
🟩 a) 3
🟦 b) 6
🟨 c) 5
🟥 d) 2
✅ Answer Key with Short Reasons
1️⃣ H⁺ → No electron, hence Bohr’s theory not applicable.
(One of the limitations of Bohr's atomic model is that it does not explain the spectra of multi-electron atoms. Bohr's theory is applicable to hydrogen like atoms or hydrogenic ions (single electron system).
All the given species like H, He⁺ and Li²⁺ are isoelectronic and have only one electron. Their electronic configurations are same and so their spectra is explained by Bohr's atomic model. But H⁺ has no electron at all and hence cannot form spectrum.)
2️⃣ Hund’s rule → Governs filling of degenerate orbitals with maximum multiplicity.
3️⃣ n = 3, l = 0 → For 3s orbital, principal quantum number = 3, azimuthal quantum number = 0.
4️⃣ 0.529 Å → Bohr radius of first hydrogen orbit.
Where aₒ is known as Bohr’s constant or Bohr radius and it the radius of first orbit of hydrogen atom and its value is 0.529 × 10⁻¹⁰ m or 0.529 × 10⁻⁸ cm or 0.529 Å or 0.0529 nm or 52.9 pm. This equation is used for the determination of nth orbit of hydrogen atom and hydrogen like ions like He⁺, Li²⁺ etc.
5️⃣Elements → Line spectrum acts as fingerprint for element identification.
6️⃣ Spherical → l = 0 corresponds to s-orbital, spherical in shape.
7️⃣ 5p → According to n + l rule, 5p fills after 4d.
8️⃣ Na and Ca → Not isoelectronic; electron counts differ.
9️⃣ Second orbit → Balmer series arises from transitions to n = 2.
1️⃣ 0️⃣ Neutron → Chadwick discovered the neutron, Nobel Prize 1935.
1️⃣1️⃣ Beta-rays → Fast moving electrons from neutron disintegration.
1️⃣2️⃣ Electrons → Cathode ray experiment proved electron existence.
1️⃣3️⃣Both values → e/m ratio constant: 1.76 × 10¹¹ C/kg or 1.76 × 10⁸ C/g.
The e/m ratio for cathode rays is constant. It is equal to 1.76 ×10¹¹ C/kg 1.76 × 10⁸ C/g. It is independent of the nature of gas in discharge tube and nature of cathode or electrodes of tube. This shows that an electron is a universal fundamental particle. It is equal to the ratio of e/m for an electron as cathode rays consist of electrons.
e/m ratio = Charge on electron/mass of electron = 1.6 × 10⁻¹⁹C/9.1 × 10⁻³¹ kg = 1.758820 × 10¹¹ C/kg
1️⃣4️⃣1.6022 × 10⁻¹⁹ C → Fundamental charge of electron.
1️⃣5️⃣ 9.1096 × 10⁻³¹ kg → Standard electron mass.
1️⃣6️⃣ Electron → Relative mass = 1/1836 of hydrogen atom.
1️⃣7️⃣ Dependent → e/m ratio varies with gas type (mass differences).
1️⃣8️⃣ Artificial radioactivity → Induced by bombardment of particles.
1️⃣9️⃣ Hydrogen → Lightest element → highest e/m ratio.
Since the e/m ratio depends upon the mass of particle, therefore, element with least mass would have highest e/m ratio. H is the lightest element, so e/m ratio of positive particle of H would be highest.
2️⃣0️⃣ Alpha rays → Helium nuclei, doubly charged, mass = 4 amu.
2️⃣ 1️⃣ Stream of Helium nuclei → Alpha rays are doubly charged helium nuclei (⁴He²⁺).
2️⃣2️⃣ Pitch-blende → Uranium mineral (U₃O₈) where Becquerel discovered radioactivity.
2️⃣3️⃣Radium & Polonium → Discovered by Marie and Pierre Curie.
2️⃣4️⃣Becquerel rays → Early name for nuclear rays after their discoverer.
2️⃣5️⃣100 times greater than beta rays → Due to heavy mass and charge of alpha particles.
2️⃣6️⃣10,000 times greater than gamma rays → Alpha rays have highest ionization power.
2️⃣7️⃣Carbon-14 → Used in radiocarbon dating of fossils and artefacts.
2️⃣8️⃣Gamma rays → Electromagnetic radiation traveling at speed of light.
2️⃣9️⃣Shorter wavelength → Gamma rays have shorter wavelength than most X-rays, hence more energetic.
3️⃣0️⃣Photons → Gamma rays are photons emitted when nuclei return to ground state.
3️⃣1️⃣ J. J. Thomson → Demonstrated cathode rays are negatively charged particles (electrons).
3️⃣2️⃣Gamma rays → Highest energy, hence greatest penetration power (γ > β > α).
3️⃣3️⃣Electron → Least mass → highest e/m ratio.
3️⃣4️⃣Deuterium & α-particle → Both have identical e/m ratio (+½).
e/m ratio depends on charge and mass. deuterium and an alpha particle has an identical ratio of e/m ratio. The e/m ratio of the alpha particle is 4.82245 × 10⁷ C/kg which is identical with deuterium.
e/m ratio of deuterium = +½
e/m ratio of α-particle = +2/4 = +½
3️⃣5️⃣Not true: speed of light → Cathode rays are material particles, slower than light.
3️⃣6️⃣Neutron is chargeless → Its lack of charge delayed discovery.
3️⃣7️⃣One α and two β emissions → Converts Th-231 to Th-227.
3️⃣8️⃣Much smaller than cathode rays → Positive rays have higher mass, lowering e/m ratio.
3️⃣9️⃣2 protons & 2 neutrons → Alpha particle = helium nucleus.
4️⃣0️⃣Electron < Proton < Neutron → Correct mass order; neutron slightly heavier than proton.
4️⃣1️⃣ Gamma rays → Both X-rays and gamma rays are electromagnetic radiations.
4️⃣2️⃣Very high → X-rays are highly energetic with very high frequency and short wavelength.
4️⃣3️⃣0.1–10 Å → Standard wavelength range of X-rays.
Wavelength of X-rays ranging from 0.01 to 10 nanometers (10⁻⁸ to 10⁻¹² meter) or 0.1 to 10Å
frequencies of X-rays ranging from 3 × 10¹⁹ Hz to 3 × 10¹⁶ Hz
energies of X-rays ranging from in the range 100 eV to 100 keV.
4️⃣4️⃣K-series → Short wavelength spectral line of X-rays.
4️⃣5️⃣Aluminium to Gold → Moseley studied X-rays of 38 metals from Al to Au.
4️⃣6️⃣Emission spectrum → Transition from higher to lower energy orbit gives emission.
4️⃣7️⃣Moseley law → √ν ∝ Z (atomic number).
4️⃣8️⃣Decrease → Wavelength decreases with increasing atomic number (inverse relation with frequency).
4️⃣9️⃣Spectrometer → Measures intensity and frequency of photon radiation.
5️⃣0️⃣Wavelength → Photon energy inversely proportional to wavelength (E = hc/λ).
5️⃣1️⃣ Frequency of light → Photon energy E=hνE = h\nu, directly proportional to frequency.
5️⃣2️⃣Continuous spectrum → Sunlight and incandescent solids emit continuous spectra.
5️⃣3️⃣Monochromatic → Single wavelength, single colour light.
5️⃣4️⃣Line spectrum → Unique to each element, acts like a fingerprint.
5️⃣5️⃣4000–4200 Å → Violet has shortest wavelength in visible region.
5️⃣6️⃣Orange → Wavelength 600–630 nm corresponds to orange colour.
5️⃣7️⃣All of them → 1 Å = 10⁻¹⁰ m = 10⁻⁸ cm = 0.1 nm = 10² pm.
5️⃣8️⃣6.625 × 10⁻³⁴ J·s → Standard value of Planck’s constant.
5️⃣9️⃣Wave number → Defined as number of waves per unit distance (inverse of wavelength).
6️⃣0️⃣Indigo → In VIBGYOR, energy decreases left to right; indigo > blue.
6️⃣1️⃣ Bulk → Continuous spectrum is a property of matter in bulk form.
6️⃣2️⃣Spectroscopy → Study of absorption/emission of electromagnetic radiation.
6️⃣3️⃣Rydberg’s constant → Expressed in cm⁻¹ or m⁻¹.
6️⃣4️⃣Band spectrum → Produced by molecules due to rotational/vibrational transitions.
6️⃣5️⃣Absorption spectrum → Shows dark lines/spaces where radiation is absorbed.
6️⃣6️⃣Hydrogen atom (H) → Single atoms produce line spectra.
6️⃣7️⃣Gamma rays → Produced in nuclear reactions; X-rays come from electronic transitions.
6️⃣8️⃣Smaller energy → Longer wavelength → lower energy (E = hc/λ).
6️⃣9️⃣Greater energy → Higher wave number (ν̅ = 1/λ) → higher energy.
7️⃣0️⃣Greater energy → Higher frequency → higher photon energy (E = hν).
7️⃣1️⃣ Smaller energy → Lesser wave number means longer wavelength → lower energy.
7️⃣2️⃣Independent of wavelength → Photon velocity = speed of light, constant.
7️⃣3️⃣Less energetic than violet → Red has longest wavelength → least energy.
7️⃣4️⃣Nucleus → Rutherford’s scattering proved existence of dense nucleus.
7️⃣5️⃣Particle nature → Bohr’s theory explained electrons as particles, ignoring wave nature.
7️⃣6️⃣h/2π → Angular momentum quantized as multiples of h/2π.
7️⃣7️⃣Emitted → Transition to lower energy releases photons.
7️⃣8️⃣Electrostatic force → Attraction between electron and nucleus provides centripetal force.
7️⃣9️⃣3.1 × 10⁻³⁴ → Angular momentum in 3rd orbit calculated by nh/2π.
Angular momentum (L₃) = nh/2𝜋 = 3 × 6.625 × 10⁻³⁴/2 × 3.142 = 3.1 × 10⁻³⁴ J.s or kg.m²/s
8️⃣0️⃣Changed always → Momentum changes between orbits; in orbits it is quantized.
8️⃣1️⃣ Multi-electron system → Bohr’s theory only explains single-electron systems.
8️⃣2️⃣Both hydrogen & hydrogenic ions → Applicable to single-electron systems like H, He⁺, Li²⁺.
8️⃣3️⃣n = 3 → Angular momentum quantization gives n = 3.
Angular momentum (L) = mvr = nh/2𝜋 ⇒ ‘n’ = 2𝜋L/h = 2 × 3.14 × 3.17 × 10⁻¹³/6.625 × 10⁻³⁴ = 3
8️⃣4️⃣3h/2π → Change in angular momentum from n=4 to n=1 orbit.
8️⃣5️⃣Stark effect → Splitting of spectral lines in electric field.
8️⃣6️⃣Zeeman effect → Splitting of spectral lines in magnetic field.
8️⃣7️⃣All of them → Bohr radius = 5.29 × 10⁻¹¹ m = 0.529 Å = 52.9 pm.
8️⃣8️⃣r ∝ n² → Radius increases with square of principal quantum number.
From Bohr’s theory; rₙ = n²aₒ showing that the radius is directly proportional to the square of principle quantum no.
8️⃣9️⃣Formula (a) → Correct derivation for nth orbit radius.
9️⃣0️⃣1.0968 × 10⁷ m⁻¹ → Standard value of Rydberg constant.
9️⃣1️⃣ 2.12 Å → Radius formula rₙ=0.529n₂
9️⃣2️⃣Formula (b) → Energy of nth orbit depends on Z²/n²
9️⃣3️⃣Formula (c) → Transition energy depends on difference in inverse squares of quantum numbers.
9️⃣4️⃣Formula (b) → Frequency derived from transition energy divided by Planck’s constant.
9️⃣5️⃣Formula (a) → Wave number = frequency/speed of light.
9️⃣6️⃣All of them → Constant K has values in J/atom, kJ/mol, and eV.
9️⃣7️⃣n² → Radius increases with square of principal quantum number.
9️⃣8️⃣4 times → First excited state (n=2) → radius = 4a₀.
9️⃣9️⃣10⁻¹¹ m → Typical order of hydrogen atom radius.
1️⃣0️⃣0️⃣6 spectral lines → Formula n(n−1)/2n(n−1)/2 → for n = 4, 6 lines.
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