Physics · Chemistry

Atomic Structure and Spectra

149 Questions

Atomic structure and spectra questions cover the Bohr model, quantum numbers, and electron transition calculations. These topics are fundamental to the physics and chemistry syllabi of competitive exams. Solving these builds confidence in handling atomic physics problems.

Bohr atomic modelHydrogen spectrum seriesElectron binding energyQuantum numbersDe Broglie wavelength

Atomic Structure and Spectra Questions

Multiple choice

The first excited state of hydrogen atom is 10.2 e V above the ground state. What temperature is needed to excite hydrogen atoms to first excited level?

  1. 7.88 x 104 K

  2. 3.94 x 104 K

  3. 5.91 x 104 K

  4. 23.65 x 104 K

  5. 17.73 x 104 K
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Where K = 1.38 x 10-23 J/mole. 0K K.E. per atom = (3/2) KT K.E. of the hydrogen atom = 10.2 eV ∴ 10.2 eV = 10.2 x (1.6 x 10-19) joule T = (2/3) x ( K.E. per atom/ K)   = (2/3) x 10.2 x (1.6 x 10-19)/1.38 x 10-23  = 7.88  x 104 K

Multiple choice

Which of the following statements is true?

  1. Rutherford used He2+ nuclei in his experiment.

  2. Orbital angular momentum depends on principal and azimuthal quantum number.

  3. Balmer series is found in atomic spectrum of hydrogen in ultraviolet region.

  4. For 3p orbital, the value of m is -1, 0 and +1.

  5. Relative bond strength of s orbital is zero.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For 3p orbital: n = 3; l = 1 Then the value of m = -l to +l = -1, 0, +1 Hence for 3p orbital, the value of m is -1, 0 and +1.

Multiple choice

Consider the following statements:

  1. An artificial satellite can be tracked very precisely from the earth by using Doppler Effect.
  2. Cosmic rays are also known as TV waves.

Which of the given statements is/are correct?

  1. Only 1

  2. Only 2

  3. Both 1 and 2

  4. Neither 1 nor 2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Statement (1) is correct. Doppler Effect is the change in frequency of a wave for an observer moving relative to its source. The radio signal received from a moving vehicle will help in tracking an artificial satellite. Statement (2) is incorrect. Radio waves are also called TV waves.

Multiple choice

The hydrogen emission spectrum consists of several series of lines named after their discoverers. Which of the following spectral series of lines are found in the infrared region?

  1. Lyman, Balmer and Paschen series

  2. Balmer, Paschen and Pfund series

  3. Paschen, Brackett, and Pfund series

  4. Paschen, Balmer and Pfund series

  5. Lyman, Balmer and Pfund series
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Paschen, Brackett and Pfund series of lines are found in the infrared region.

Multiple choice

Which of the following statements is false?

  1. Hydrogen has the simplest line spectrum among all the elements.

  2. Absorption spectrum forms when atoms or molecules are excited from lower energy level to higher energy levels.

  3. Emission spectrum forms when atoms or molecules are de-excited from higher energy level to lower energy level.

  4. Line spectra are also known as molecular spectra.

  5. Band spectrum forms due to the vibrations and rotations of atoms in molecules.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Line spectra are also called atomic spectra because the lines represent wavelengths radiated from atoms when electrons change from one energy level to another.  Band spectra are also known as molecular spectra because they are produced when the emitting substance is in the molecular state.

Multiple choice

With increasing principle quantum number, the energy diffrence betwen adjacent energy levels in H - atoms ?

  1. Decreases

  2. Increases

  3. Remain constant

  4. Decreses for low value of Z and increases for higher value of Z .
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This option is correct because ,

energy is given by , En = -13.6 / n2 eV / atom .

En -En-1 = -13.6 [ (1 / n2 ) - (1 / (n-1)2 ) ] .

This diffrence is decreases with the increase in value of ' n ' .

Hence, this option is correct .

Multiple choice

There are two isotopes of hydrogen, i.e. 1H and 2H. The ratio of radii of their first orbits, using Bohr's Theory and ignoring the reduced mass concept, is

  1. 1 : 2

  2. 1 : 1

  3. 1 : 4

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In both the isotopes, the number of protons is 1. Only the number of neutrons varies. If the reduced mass concept is not taken into account, then the radius would only depend on the central charge and not on the mass. Hence, these isotopes have the same atomic radii, although this is factually incorrect. Reduced mass concept holds in reality.

Multiple choice

Which of the following statements is true regarding the sensitivity of Electron Spin Resonance (ESR)?

  1. ESR sensitivity increases with increasing temperature and decreasing magnetic field.

  2. ESR sensitivity increases with increasing temperature and increasing magnetic field.

  3. ESR sensitivity increases with decreasing temperature and increasing magnetic field.

  4. ESR sensitivity increases with decreasing temperature and decreasing magnetic field.

  5. The sensitivity does not depend on temperature and magnetic field.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This answer is correct as we can see from the expression n1/n2 = e(-2µH/kT) that sensitivity of the instrument is greatly enhanced by using a high magnetic field and lowering the temperature.

Multiple choice

Bohr's model can explain the

  1. spectrum of hydrogen only

  2. spectrum of an atom or ion containing one electron only

  3. spectrum of hydrogen molecule

  4. solar spectrum

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The Bohr model gives almost exact results only for a system where two charged points orbit each other at speeds much less than that of light. This includes one-electron systems such as the hydrogen atom, singly ionised helium, etc.