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 treatment of hydrogen atoms prescribed by Bohr can be generalised to

  1. describe the energy level structure and electromagnetic radiation spectra of hydrogen-like ions
  2. predict fine structure of atomic spectral lines
  3. provide a method to calculate relative intensities of spectral lines

  1. Only 1

  2. Only 2

  3. Only 3

  4. Both 1 and 2

  5. 1, 2 and 3
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The treatment of hydrogen atoms prescribed by Bohr can be generalised to describe the energy level structure and electromagnetic radiation spectra of hydrogen-like ions, i.e.  a positive nucleus orbited by a single electron.

Multiple choice

For d-d transition, absorption from electronic excitation always appears as broad bands and not as sharp lines. It is due to which of the following reasons?

  1. Molecular vibrations
  2. Spin orbital coupling 3 John-Teller effect
  3. Laporte forbidden transition

  1. 1 and 2

  2. 2 and 3

  3. 1, 3 and 4

  4. 1, 2 and 3

  5. 2, 3 and 4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For d-d transition, absorption from electronic excitation always appears as broad bands and not as sharp lines. It is due to molecular vibration, spin orbital coupling and John-Teller effect.

Multiple choice

Which of the following statements is/are incorrect? A. Balmer series falls in the ultraviolet range of electromagnetic radiation. B. The emission and absorption spectra of hydrogen like atoms is explained nicely by Bohr’s concept of stationary state of electrons. C. Atomic spectrum is band spectrum while molecular spectrum is a line spectrum.

  1. Only A

  2. Only B

  3. Only C

  4. Only A and B

  5. Only A and C
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Wrong statement: Balmer series falls in the ultraviolet range of electromagnetic radiation.

Balmer series falls in the visible range of electromagnetic radiation.

Wrong statement: Atomic spectrum is a band spectrum while molecular spectrum is a line spectrum.

Atomic spectrum is line spectrum while molecular spectrum is a band spectrum.

Multiple choice

Bohr model can explain

  1. the spectrum of hydrogen atom only

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

  3. the spectrum of hydrogen molecule

  4. the solar spectrum

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

Bohr model can explain the spectrum of an atom or ion containing one electron only.

Multiple choice

Which of the following statements is correct?

  1. The different energy levels are equally spaced.

  2. The energy of the electron decreases as the value of n increases.

  3. The energy of the electrons in an atom is negative.

  4. Bohr's theory explains the spectrum of multi-electron atoms.

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

An electron in an atom has negative energy because it is in a bound state. That means that it cannot escape the atom unless it is given energy.

Multiple choice

Radius of hydrogen atom is of the order of _____ .

  1. 1 nm

  2. 1 A�

  3. 1 cm

  4. 0.1 A�
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The atomic radius of a hydrogen atom is approximately 0.05 nm, which is equivalent to 0.5 Angstroms (A). Among the choices, 1 Angstrom is the closest order of magnitude.

Multiple choice chemistry periodicity periodic trends in physical properties properties and trend trends in periodic table electronic configuration and valency electron configuration

The $Z _{effective}$ for $He$ is?

  1. 2

  2. 1.7

  3. 1.85

  4. 1.65
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The effective nuclear charge experienced by a 1s electron in helium is +1.70.

The effective nuclear charge $Z _{eff}$ is the net positive charge experienced by an electron in a multi-electron atom.

A given electron does not experience a full nuclear charge because the other electrons are sometimes between it and the nucleus and shield it from the nucleus.

The formula for effective nuclear charge is-

$Z _{eff}=Z-S$

where, 
Z is the number of protons in the nucleus, and S is the shielding constant, the average number of electrons between the nucleus and the electron in question.
The American physicist John Slater derived a number of rules to determine the shielding constant.

He found that for electrons in a 1s orbital, the second electron shields the first by 0.30 units.

$Z _{eff}=Z-S=2- 0.30-1.70$

Hence, the correct option is B.


Multiple choice bohr's model of atom structure of atom

What is the lowest energy of the spectral line emitted by the hydrogen atom in the Lyman series? (h=Plank constant; C=Velocity of light; R=Rydberg constant)

  1. $\dfrac{5hcR}{36}$
  2. $\dfrac{4hcR}{3}$
  3. $\dfrac{3hcR}{4}$
  4. $\dfrac{7hcR}{144}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Use the formula,
$ 1/\lambda = R \times \left ( 1/n _1^2 - 1/n _2^2 \right) $.
Therefore,
$ \Delta E = hc/\lambda = hcR \times \left ( 1/n _1^2 - 1/n _2^2 \right) $.
for Lyman series lowest energy transition is from n$=1 $ to n$=2$.

Multiple choice bohr's model of atom structure of atom

The ratio of the wave numbers of the radiation corresponding to the third line of Balmer series and the second line of the Paschen series of hydrogen spectrum is:

  1. 21/16 x 9/4

  2. 25/16 x 9/4

  3. 21/25 x 9/4

  4. 16/25 x 9/4
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Use the formula,
Wavenumber = $ R \times \left ( 1/n _1^2 - 1/n _2^2 \right ) $.
For third line Balmer series $ n _1=2$ and $n _2=5 $.
For second line Paschen series $ n _1=3$ and $n _2=5 $
Therefore the ratio is $ \left (1/4 - 1/25 \right) / \left (1/9 - 1/25 \right) $ which equals 
$ 21/16 \times 9/4 $. 

Multiple choice bohr's model of atom structure of atom

What are the values of $n _{1}$ and $n _{2}$ respectively for $H _{\beta}$ line in the Lyman series of hydrogen atomic spectrum?

  1. 3 and 5

  2. 2 and 3

  3. 1 and 3

  4. 2 and 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The $\beta$ line of any series means the second line of that series. Similarly the $\alpha$ line implies the first line and the $\gamma$ line implies the third line of the series.

Multiple choice bohr's model of atom structure of atom

The first emission line of hydrogen atomic spectrum in the Balmer series appears at (R = Rydberg constant):

  1. $\frac{5R}{36}cm^{-1}$
  2. $\frac{3R}{4}cm^{-1}$
  3. $\frac{7R}{144}cm^{-1}$
  4. $\frac{9R}{400}cm^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Use the formula ,
wavenumber =R×(1/n21−1/n22)=R×(1/n12−1/n22).

Multiple choice bohr's model of atom structure of atom

The spectrum of helium is expected to be similar to that of:

  1. $H$
  2. $Li^+$
  3. $Na$
  4. $He^+$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

No. of electrons in$Li^{+}$ & $He = 2$. Therefore the spectrum will be same for both of them with same no. of electrons.

Multiple choice bohr's model of atom structure of atom

The distance between 3rd and 2nd orbits in the hydrogen atom is:

  1. $2.646\times {10}^{-8}cm$
  2. $2.116\times {10}^{-8}cm$
  3. $1.058\times {10}^{-8}cm$
  4. $2.646\times {10}^{-10}cm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Solution:

Distance between the 2nd and the 3rd orbits = distance of 3rd orbit – distance of second orbit from the nucleus.

${ d } _{ 3 }=\frac { 0.529\times { n }^{ 2 } }{ z\times { 10 }^{ -10 }m } $

$=0.529\times 9\times { 10 }^{ -10 }m$

${ d } _{ 2 }=0.529\times 4\times { 10 }^{ -10 }m$

${ d } _{ 3 }–{ d } _{ 2 }=0.529\times 5\times { 10 }^{ -10 }m$

  $=2.645\times { 10 }^{ -10 }m$  is the distance between the 2nd the 3rd orbits.