Physics · Chemistry

Atomic Structure and Spectra

113 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

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

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.

 
 

Multiple choice

What affects the ionisation energy of an element?

Ionisation energy of an atom or molecule describes the minimum amount of energy required to remove an electron from the atom or molecule in the gaseous state.

X   +  energy---->  X+ + e-

  1. Atomic size

  2. Electron affinity

  3. Electronegativity

  4. Neutron

  5. Proton
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In small atoms, electrons remains close to the  nucleus and they have more nuclear attraction, so more energy is required to remove electrons from small atoms. In small atoms, electrons remains close to the nucleus and they have more nuclear attraction, so more energy is required to remove electrons from small atoms.

Multiple choice

Which of the following statements is not true?

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

  2. Absorption spectrum is formed when atoms or molecules are excited from a lower energy level to a higher energy level.

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

  4. Line Spectra are also known as molecular spectra.

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

This option is correct because this statement is not true. 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.