- In the Bohr model, what does the angular momentum of an electron in orbit depend on?
A) Mass of the electron
B) Radius of the orbit
C) Principal quantum number (n)
D) All of the above
Answer: D) All of the above.
Explanation: The angular momentum of an electron in orbit is determined by its mass, the radius of the orbit, and is quantized according to the principal quantum number (n).
- Which series of transitions in hydrogen involves infrared radiation?
A) Lyman series
B) Balmer series
C) Paschen series
D) Brackett series
Answer: C) Paschen series.
Explanation: The Paschen series corresponds to transitions that fall to the n=3 level, resulting in infrared emissions.
- What does the term “ionization energy” refer to?
A) Energy required to move an electron to a higher orbit
B) Energy required to remove an electron from an atom
C) Energy released when an electron is added to an atom
D) Energy required to excite an electron
Answer: B) Energy required to remove an electron from an atom.
Explanation: Ionization energy is the energy needed to completely remove an electron from an atom in its ground state.
- What type of spectrum is produced by excited hydrogen gas?
A) Continuous spectrum
B) Emission spectrum
C) Absorption spectrum
D) Black body spectrum
Answer: B) Emission spectrum.
Explanation: An emission spectrum is produced when electrons in excited states fall back to lower energy levels, emitting specific wavelengths of light.
- In the Bohr model, what is the effect of increasing the principal quantum number (n) on the radius of the orbit?
A) The radius decreases.
B) The radius increases.
C) The radius remains constant.
D) The radius becomes infinite.
Answer: B) The radius increases.
Explanation: As n increases, the radius of the electron’s orbit also increases, placing the electron further from the nucleus.
- Which of the following is true about the quantization of energy levels in the Bohr model?
A) Energy levels are continuous.
B) Energy levels are discrete.
C) Energy levels are undefined.
D) Energy levels vary randomly.
Answer: B) Energy levels are discrete.
Explanation: The Bohr model introduces the concept of quantized energy levels, where electrons can only occupy specific energy states.
- What is the main limitation of the Bohr model concerning multi-electron atoms?
A) It can only explain hydrogen-like atoms.
B) It cannot predict ionization energies.
C) It assumes electrons are in fixed orbits.
D) It neglects angular momentum.
Answer: A) It can only explain hydrogen-like atoms.
Explanation: The Bohr model primarily applies to hydrogen and does not adequately describe the more complex interactions in multi-electron atoms.
- When an electron drops from a higher energy level to a lower one, what occurs?
A) Ionization
B) Absorption of energy
C) Emission of energy
D) No energy change
Answer: C) Emission of energy.
Explanation: The transition of an electron from a higher to a lower energy level results in the emission of energy, typically in the form of a photon.
- Which quantum number determines the shape of an orbital?
A) Principal quantum number (n)
B) Azimuthal quantum number (l)
C) Magnetic quantum number (m)
D) Spin quantum number (s)
Answer: B) Azimuthal quantum number (l).
Explanation: The azimuthal quantum number (l) indicates the shape of the orbital, with different values corresponding to different shapes (s, p, d, f).
- How does the energy of an electron change as it moves to a lower energy level?
A) It increases.
B) It decreases.
C) It remains constant.
D) It fluctuates.
Answer: B) It decreases.
Explanation: When an electron moves to a lower energy level, it loses energy, often releasing it as a photon.
- Which spectral series is observed when electrons transition to the second energy level in hydrogen?
A) Lyman series
B) Balmer series
C) Paschen series
D) Brackett series
Answer: B) Balmer series.
Explanation: The Balmer series corresponds to transitions to the n=2 level, resulting in visible light emissions.
- What physical concept does the Bohr model introduce to explain electron behavior?
A) Wave-particle duality
B) Conservation of mass
C) Quantization of energy levels
D) Thermodynamic equilibrium
Answer: C) Quantization of energy levels.
Explanation: The Bohr model introduces the concept that electrons occupy discrete energy levels rather than any arbitrary value.
- In a hydrogen atom, which transition corresponds to the emission of a photon with the shortest wavelength?
A) n=2 to n=1
B) n=3 to n=2
C) n=4 to n=1
D) n=5 to n=4
Answer: C) n=4 to n=1.
Explanation: The transition from n=4 to n=1 releases the most energy, resulting in the shortest wavelength of emitted light.
- What do the lines in a spectral emission spectrum represent?
A) Continuous range of colors
B) Absorption of light
C) Specific wavelengths emitted by electrons
D) Random energy emissions
Answer: C) Specific wavelengths emitted by electrons.
Explanation: Each line corresponds to a specific transition between energy levels, indicating the precise wavelengths of light emitted.
- Which principle governs the stability of electron orbits in the Bohr model?
A) Uncertainty principle
B) Exclusion principle
C) Wave nature of electrons
D) Quantization of angular momentum
Answer: D) Quantization of angular momentum.
Explanation: The Bohr model posits that electron orbits are stable due to quantized angular momentum, defined by the relation
L=nℏ.
- Which factor does not influence the energy levels in a hydrogen atom?
A) Atomic number
B) Principal quantum number
C) Electron spin
D) Distance from the nucleus
Answer: A) Atomic number.
Explanation: The energy levels of hydrogen depend on the principal quantum number, but since hydrogen has only one proton, the atomic number is not a factor.
- Which of the following correctly describes the Balmer series?
A) Transitions to n=1 producing ultraviolet light.
B) Transitions to n=2 producing visible light.
C) Transitions to n=3 producing infrared light.
D) Transitions to n=4 producing X-rays.
Answer: B) Transitions to n=2 producing visible light.
Explanation: The Balmer series involves transitions to the second energy level, resulting in the emission of visible light.
- What occurs during the process of electron excitation in an atom?
A) The atom loses mass.
B) An electron gains energy and moves to a higher energy level.
C) An electron is removed from the atom.
D) The nucleus emits radiation.
Answer: B) An electron gains energy and moves to a higher energy level.
Explanation: Excitation involves an electron absorbing energy and transitioning to a higher orbit.
- In the hydrogen atom, what does the term “ground state” refer to?
A) The highest energy state.
B) The state with the least energy.
C) The state when the atom is ionized.
D) The state with multiple excited electrons.
Answer: B) The state with the least energy.
Explanation: The ground state is the lowest energy configuration of an atom, corresponding to n=1 in the hydrogen atom.
- Which quantum number is related to the spin of an electron?
A) Principal quantum number (n)
B) Azimuthal quantum number (l)
C) Magnetic quantum number (m)
D) Spin quantum number (s)
Answer: D) Spin quantum number (s).
Explanation: The spin quantum number (s) describes the intrinsic angular momentum or “spin” of an electron, which can be either +1/2 or -1/2.
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