Atomic models and Bohr theory
Learn the historical development of atomic models, especially the Bohr model, and how it explains the structure, radii, and energy levels of hydrogen and hydrogen-like atoms.
Why this shows up in the exam
NEET tests your understanding of atomic structure, Bohr's postulates, and calculations involving radii, energy, and electron velocity.
How NEET tests this
Learn the idea
Bohr model treats electrons as moving in fixed circular orbits where only certain radii and energies are allowed; the key insight is that angular momentum is quantized in integral multiples of h/2π, which directly gives the discrete energy levels.
🧠 Memory hook: Bohr’s B‑n‑h rule – **B**ounce in **n** circles, each step adds **h/2π** to angular momentum
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- Allowed orbit: n h/2π = m v r (n = 1,2,3…)
- Radius of nth orbit: rₙ = n² a₀ / Z (a₀ = 0.529 Å)
- Energy of nth level: Eₙ = –13.6 Z² / n² eV
- Total energy = kinetic + potential = – kinetic
- Frequency of emitted photon: ν = ΔE / h
How to approach it
- 1Read the question and note the atomic number Z and the principal quantum numbers involved
- 2Write the required Bohr formula (radius, energy or velocity) using the given n and Z
- 3Substitute the numbers; keep track of sign for energy (negative for bound states)
- 4If the question asks for a ratio or difference, use the formula directly before plugging values
Worked example — watch it click
The first use of quantum theory to explain the structure of atom was made by
- A)Heisenberg
- ✅Bohr
- C)Planck
- D)Einstein
The concept behind this problem
The example checks whether you know which scientist first applied quantum ideas to the internal structure of the atom, not who originally introduced the quantum concept itself.
Step by step
- 1Niels Bohr first applied quantum theory to atomic structure in 1913, proposing quantized angular momentum and energy levels.
- 2Planck introduced quantum theory for blackbody radiation, but Bohr applied it to atomic structure.
Watch out
Students often pick Planck because he originated quantum theory, but the first application to atomic structure was Bohr.
Common slip-ups that cost marks
- •Confusing kinetic energy (positive) with total energy (negative)
- •Using Z=1 for all cases – remember hydrogen‑like ions need Z in the formulas
- •Mixing up n (principal quantum number) with orbital quantum number l
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Practise it
These are real questions from past NEET papers that test this exact idea.
The total energy of an electron in the nth stationary orbit of the hydrogen atom can be obtained by:
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