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Class 12 Atoms worksheet
CBSE Physics. Rutherford scattering, Bohr orbits and energies, hydrogen spectrum series. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.
Sample questions
Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.
Section A · multiple choice
- 1.
The radius of the 3rd Bohr orbit in a hydrogen atom is: (r₁ = 0.53 Å for hydrogen)
- 14.31 Å
- 1.59 Å
- 9.54 Å
- 4.77 Å
Answer
(d) 4.77 Å
rₙ = n²r₁/Z = 3² × 0.53/1
- 2.
The energy of an Li²⁺ ion with its electron in the n = 5 level is:
- −4.896 eV
- −8.16 eV
- 4.896 eV
- −0.544 eV
Answer
(a) −4.896 eV
Eₙ = −13.6Z²/n² eV with Z = 3
- 3.
The energy of the photon emitted when a hydrogen electron falls from n = 3 to n = 2 is:
- 1.51 eV
- 2.27 eV
- 3.4 eV
- 1.89 eV
Answer
(d) 1.89 eV
13.6(1/2² − 1/3²)
Section B · short answer
- 4.
For the electron in the n = 3 orbit of a hydrogen atom, find its kinetic energy, potential energy and total energy.
Answer
KE = 1.51 eV; PE = −3.02 eV; total = −1.51 eV
KE = −E, PE = 2E, E = −13.6Z²/n²
- 5.
Find the energy and wavelength of the photon emitted when a hydrogen electron falls from n = 7 to n = 3. (hc = 1240 eV nm)
Answer
1.23 eV; 1,005.22 nm
ΔE = 13.6(1/3² − 1/7²); λ = 1240/ΔE
Section C · long answer
- 6.
A hydrogen atom with its electron in the n = 2 level absorbs a photon of 3.02 eV. To which level does the electron rise? List the photon energies it can emit as it falls back to n = 2.
Answer
n = 6; 3→2: 1.89 eV, 4→2: 2.55 eV, 5→2: 2.856 eV, 6→2: 3.02 eV, 4→3: 0.66 eV, 5→3: 0.97 eV, 6→3: 1.13 eV, 5→4: 0.306 eV, 6→4: 0.47 eV, 6→5: 0.17 eV
−13.6/2² + 3.02 = −13.6/n²
Fresh sheets for your child
In the app, every Atoms sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.
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