JEE Main Atomic Structure 2027 — Bohr Model, Quantum Numbers, Orbitals, de Broglie and 35 Practice MCQs

May 5, 2026 · CLAT Gurukul · Blog

Last Updated: May 2026

JEE 2027 — Atomic Structure overview

For JEE Main 2027 Atomic Structure, expect 2-3 questions covering Bohr’s model numerics, quantum numbers, orbital configuration, photoelectric effect formulas and de Broglie wavelength. The chapter sits at the foundation of physical chemistry and bridges into modern physics in JEE Physics — making formula-recall here doubly valuable.

Bohr Model — Master Formulas

Quantity	Formula	Notes
Radius of nth orbit (H)	r_n = 0.529 × n² /Z Å	0.529 Å = Bohr radius
Velocity in nth orbit	v_n = 2.18 × 10⁶ × Z/n m/s	—
Energy of nth orbit	E_n = –13.6 × Z²/n² eV	For H: −13.6, −3.4, −1.51, −0.85 eV
Energy in joules	E_n = –2.18 × 10⁻¹⁸ × Z²/n² J	—
Frequency of transition	ν = (E_i – E_f)/h	h = 6.626 × 10⁻³⁴ J·s
Rydberg formula	1/λ = R_H·Z²(1/n₁² – 1/n₂²)	R_H = 1.097 × 10⁷ m⁻¹

Hydrogen Spectrum Series

Series	Final n (n₁)	Region	First line λ
Lyman	1	Ultraviolet	121.6 nm
Balmer	2	Visible	656.3 nm (Hα, red)
Paschen	3	Infrared	1875 nm
Brackett	4	Far infrared	4050 nm
Pfund	5	Far infrared	7460 nm

Photoelectric Effect

Einstein’s equation: hν = φ + KE_max
φ = work function = hν₀ (threshold frequency)
Stopping potential: eV_s = KE_max = h(ν − ν₀)
KE_max depends on frequency, not intensity
Number of electrons emitted depends on intensity, not frequency

de Broglie Wavelength

λ = h/p = h/(mv)
For an electron accelerated through V volts: λ = 12.27/√V Å (where V is in volts)
Photon: p = h/λ; E = pc

Heisenberg Uncertainty Principle

Δx · Δp ≥ h/(4π) — applies to conjugate variables (position-momentum, energy-time). Cannot simultaneously know exact position and momentum.

Quantum Numbers

Quantum No.	Symbol	Range	Determines
Principal	n	1, 2, 3,…	Energy, size of orbit
Azimuthal	l	0 to (n−1)	Subshell shape (s, p, d, f)
Magnetic	m_l	–l to +l	Orbital orientation
Spin	m_s	+½, –½	Electron spin

Aufbau: Fill orbitals in order of increasing (n+l), with lower n first when (n+l) is equal. Pauli’s exclusion: No two electrons in an atom can have all four quantum numbers identical. Hund’s rule: Maximum unpaired electrons in degenerate orbitals before pairing.

Number of Orbitals and Electrons

Total orbitals in nth shell: n²
Total electrons in nth shell: 2n²
s subshell: 1 orbital, 2 electrons
p subshell: 3 orbitals, 6 electrons
d subshell: 5 orbitals, 10 electrons
f subshell: 7 orbitals, 14 electrons

Number of Radial and Angular Nodes

Radial nodes = n − l − 1
Angular nodes = l
Total nodes = n − 1

35 Practice MCQs

Bohr radius for H is — (A) 0.529 Å (B) 1.058 Å (C) 5.29 Å (D) 0.0529 Å
Energy of H atom in n=1 — (A) −13.6 eV (B) −3.4 eV (C) +13.6 eV (D) 0
Energy of H atom in n=2 — (A) −13.6 eV (B) −3.4 eV (C) −1.51 eV (D) −0.85 eV
Lyman series lies in — (A) UV (B) visible (C) IR (D) far IR
Balmer series lies in — (A) UV (B) visible (C) IR (D) microwave
Hα line is in — (A) Lyman (B) Balmer (C) Paschen (D) Pfund
Number of orbitals in n=3 — (A) 1 (B) 4 (C) 9 (D) 16
Maximum electrons in n=3 — (A) 2 (B) 8 (C) 18 (D) 32
Number of f orbitals — (A) 1 (B) 3 (C) 5 (D) 7
Maximum value of m_l for l=2 — (A) ±1 (B) ±2 (C) ±3 (D) 0
3p subshell electrons — (A) 2 (B) 6 (C) 10 (D) 14
de Broglie wavelength of an electron at 100 V is — (A) 12.27 Å (B) 1.227 Å (C) 0.1227 Å (D) 12.27 nm
Heisenberg’s principle: Δx·Δp ≥ — (A) h (B) h/2 (C) h/(4π) (D) h/π
Threshold frequency for K (work function 2.3 eV) — (A) 5.55×10¹⁴ Hz (B) 1.0×10¹⁵ Hz (C) 1.5×10¹⁵ Hz (D) 7.0×10¹⁴ Hz
Stopping potential depends on — (A) frequency (B) intensity (C) both (D) neither
Photoelectric current depends on — (A) frequency (B) intensity (C) both (D) neither
The Aufbau order: 4s vs 3d — fills first — (A) 3d (B) 4s (C) simultaneously (D) depends on element
Cu electronic config — (A) [Ar]3d⁹4s² (B) [Ar]3d¹⁰4s¹ (C) [Ar]3d¹⁰4s² (D) [Ar]3d⁸4s²
Cr electronic config — (A) [Ar]3d⁴4s² (B) [Ar]3d⁵4s¹ (C) [Ar]3d⁶4s⁰ (D) [Ar]3d³4s³
Total nodes in 3p orbital — (A) 0 (B) 1 (C) 2 (D) 3
Radial nodes in 3p — (A) 0 (B) 1 (C) 2 (D) 3
Angular nodes in 4d — (A) 0 (B) 1 (C) 2 (D) 4
Quantum number determining orbital shape — (A) n (B) l (C) m_l (D) m_s
For 4s subshell: l = (A) 0 (B) 1 (C) 2 (D) 3
Pauli’s exclusion principle states — (A) no two electrons same quantum numbers (B) electrons fill lowest energy first (C) maximize unpaired (D) all are random
Speed of electron in n=2 of H = — (A) 1.09×10⁶ m/s (B) 2.18×10⁶ m/s (C) 4.36×10⁶ m/s (D) 1.5×10⁷ m/s
Hund’s rule applies to — (A) degenerate orbitals (B) different shells (C) all atoms (D) noble gases
Wavelength of first line of Lyman series of H ≈ — (A) 121.6 nm (B) 656.3 nm (C) 91.2 nm (D) 410 nm
The number of electrons with n=3, l=2 in iron — (A) 6 (B) 5 (C) 4 (D) 0 (no 3d in Fe? actually Fe = [Ar]3d⁶4s²)
Photon momentum p = (A) hν/c (B) hλ (C) h/c (D) hc
Compton effect demonstrated — (A) wave nature of light (B) particle nature of light (C) wave nature of matter (D) zero rest mass
Davisson-Germer experiment proved — (A) wave nature of electrons (B) particle nature (C) Bohr’s model (D) Pauli’s principle
Schrödinger equation gives — (A) wave function ψ (B) trajectory (C) classical orbit (D) field
The probability density is — (A) ψ (B) ψ² (C) ψ⁻¹ (D) ψ + ψ*
Zeeman effect is — (A) splitting of spectral lines in magnetic field (B) photoelectric (C) Compton (D) Doppler

Answer Key

1-A, 2-A, 3-B, 4-A, 5-B, 6-B, 7-C, 8-C, 9-D, 10-B, 11-B, 12-B, 13-C, 14-A, 15-A, 16-B, 17-B, 18-B, 19-B, 20-C, 21-B, 22-C, 23-B, 24-A, 25-A, 26-A, 27-A, 28-A, 29-A, 30-A, 31-B, 32-A, 33-A, 34-B, 35-A

FAQ

How many questions from Atomic Structure in JEE Main 2027?

Typically 2–3 questions, mostly numerical (Bohr radius/energy, de Broglie, photoelectric).

Should I memorise spectrum series wavelengths?

Memorise the series names + their final n + spectrum region. Specific wavelengths are derivable from Rydberg’s formula in the exam.

Which is the highest-yield formula here?

Rydberg’s: 1/λ = R_H·Z²(1/n₁² − 1/n₂²). Combined with E_n = −13.6Z²/n² eV, these two cover 70% of JEE Atomic Structure numerics.

Are anomalous configs of Cr, Cu important?

Yes — Cr [Ar]3d⁵4s¹ and Cu [Ar]3d¹⁰4s¹ are recurrent JEE asks for “exception to Aufbau”.