How much of JEE Main comes from Atomic Structure?

JEEGenie estimates about 3% of JEE Main marks come from Atomic Structure, based on recent papers. The share varies from year to year.

Which formulas matter most in Atomic Structure?

The Atomic Structure sheet on this page has 16 formula entries, starting with Atomic Number (Z) & Mass Number (A), Bohr's Model of Hydrogen Atom, Energy of Electron in H-like Atom, Radius of Bohr Orbit, Velocity of Electron in Bohr Orbit. Each one comes with when to use it and the trap to avoid.

What topics does Atomic Structure cover for JEE?

Atomic Structure covers Bohr's Model, Quantum Numbers, Atomic Orbitals, Electronic Configuration, Dual Nature and de Broglie, Heisenberg Uncertainty Principle.

How should I revise Atomic Structure before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Atomic Structure questions on JEEGenie.

How many previous-year questions are there on Atomic Structure?

JEEGenie has 373 previous-year questions on Atomic Structure, and this page shows a few with worked explanations.

Is practice on Atomic Structure free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Atomic Structure for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 3% of JEE Main marks come from Atomic Structure. This page covers 16 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Confusing atomic number with mass number; Z defines element identity.

Key points to know

Atomic Number (Z) & Mass Number (A). Atomic number Z is the number of protons; mass number A is the sum of protons and neutrons. Isotopes have same Z, different A.
Bohr's Model of Hydrogen Atom. Electrons revolve in fixed circular orbits (shells) with quantized angular momentum. Energy is quantized and negative for bound states.
Spectral Series of Hydrogen. Lyman (UV): n1=1; Balmer (visible): n1=2; Paschen (IR): n1=3; Brackett (IR): n1=4; Pfund (IR): n1=5.
de Broglie Wavelength. Matter has wave nature; wavelength inversely proportional to momentum.
Quantum Numbers. Four quantum numbers define an electron: n (shell), l (subshell, 0 to n-1), m_l (orbital, -l to +l), m_s (spin, ±1/2).
Shapes of Orbitals. s orbitals spherical; p orbitals dumbbell (three: px, py, pz); d orbitals cloverleaf (five).
Aufbau Principle, Pauli Exclusion, Hund's Rule. Aufbau: electrons fill lowest energy orbitals first. Pauli: no two electrons have same four quantum numbers. Hund: each orbital in subshell gets one electron before pairing.
Photoelectric Effect. Light ejects electrons from metal surface if frequency > threshold. Kinetic energy of ejected electron = hν - φ.
Ionization Energy and Spectral Transitions. Ionization energy is energy to remove electron from ground state (n=1 to ∞). For hydrogen, IE = 13.6 eV.
Rydberg Constant and Its Units. Rydberg constant R_H = 1.097 × 10^7 m^-1. Used in Rydberg formula for hydrogen spectrum.
Electromagnetic Spectrum Regions. Order: Radio, Microwave, IR, Visible, UV, X-ray, Gamma. Wavelength decreases, frequency and energy increase.

Formula sheet

Name	Formula	When to use
Atomic Number (Z) & Mass Number (A)	$Z = protons$ $A = protons + neutrons$	When identifying elements, calculating neutrons, or dealing with isotopes.
Bohr's Model of Hydrogen Atom	$m v r = \frac{n h}{2 π}$ $E_{n} = - \frac{13.6}{n^{2}} eV$ $r_{n} = 0.529 \times n^{2} \overset{˚}{A}$	For hydrogen atom energy levels, radii, and spectral lines.
Energy of Electron in H-like Atom	$E_{n} = - 13.6 \frac{Z^{2}}{n^{2}} eV$ $E_{n} = - 2.18 \times 10^{- 18} \frac{Z^{2}}{n^{2}} J$	For H, He+, Li2+ etc. to find energy of any orbit.
Radius of Bohr Orbit	$r_{n} = 0.529 \frac{n^{2}}{Z} \overset{˚}{A}$ $r_{n} = 5.29 \times 10^{- 11} \frac{n^{2}}{Z} m$	To find orbit radius for H-like atoms.
Velocity of Electron in Bohr Orbit	$v_{n} = 2.18 \times 10^{6} \frac{Z}{n} m/s$	To find speed of electron in any Bohr orbit.
Wavelength of Emitted Photon (Rydberg Formula)	$\frac{1}{λ} = R_{H} (\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}})$ $R_{H} = 1.097 \times 10^{7} m^{- 1}$ $Δ E = 13.6 (\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}) eV$	For calculating wavelength or energy of spectral lines in hydrogen.
Calculating Number of Spectral Lines	$Number of lines = \frac{n (n - 1)}{2}$ where n is the initial principal quantum number.	When electron de-excites from a high energy level to ground state.
de Broglie Wavelength	$λ = \frac{h}{p} = \frac{h}{m v}$	For particles like electrons, protons, neutrons to find wavelength.
Heisenberg Uncertainty Principle	$Δ x \cdot Δ p \geq \frac{h}{4 π}$ $Δ x \cdot Δ (m v) \geq \frac{h}{4 π}$	When dealing with microscopic particles and their dual nature.
Number of Nodes	$Total nodes = n - 1$ $Angular nodes = l$ $Radial nodes = n - l - 1$	To find number of nodes in any orbital.
Photoelectric Effect	$K E_{max} = h ν - ϕ$ $ϕ = h ν_{0}$ (threshold frequency)	When light interacts with metal and ejects electrons.
Energy of Photon	$E = h ν = \frac{h c}{λ}$	For any electromagnetic radiation.
Ionization Energy and Spectral Transitions	$I E = E_{\infty} - E_{1} = 13.6 eV$	Calculating energy to remove electron.
Calculating Wavelength from Energy Difference	$λ = \frac{h c}{Δ E}$ $Δ E = 13.6 (\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}) eV$	For any electronic transition in hydrogen.
Rydberg Constant and Its Units	$R_{H} = 1.097 \times 10^{7} m^{- 1}$ $R_{H} = 109677 {cm}^{- 1}$	In Rydberg formula for spectral lines.
Energy Conversion: eV to Joules	$1 eV = 1.602 \times 10^{- 19} J$	Whenever energy is given in eV and formula uses Joules.

Open the Atomic Structure formula page

What JEE asks

Atomic Number (Z) & Mass Number (A). JEE often asks to find number of neutrons from Z and A, or identify isotopes in a list.
Bohr's Model of Hydrogen Atom. JEE asks to calculate energy difference for transitions, or radius for given n.
Energy of Electron in H-like Atom. JEE gives Z and n, asks energy in eV or J, or compares energies.
Radius of Bohr Orbit. JEE asks radius for given n and Z, or compares radii of different species.
Velocity of Electron in Bohr Orbit. JEE asks velocity for given n and Z, or compares speeds.
Wavelength of Emitted Photon (Rydberg Formula). JEE gives transition, asks wavelength or energy; or identifies series (Lyman, Balmer etc.).
Spectral Series of Hydrogen. JEE asks which series a given transition belongs to, or which series is in visible region.
Calculating Number of Spectral Lines. JEE gives initial n, asks total number of spectral lines emitted.
de Broglie Wavelength. JEE gives mass and velocity, asks de Broglie wavelength.
Heisenberg Uncertainty Principle. JEE asks to calculate minimum uncertainty in position or momentum.
Quantum Numbers. JEE gives set of quantum numbers, asks if valid or not.
Shapes of Orbitals. JEE asks number of angular nodes or radial nodes, or shape identification.
Number of Nodes. JEE gives orbital (e.g., 3p), asks number of radial nodes.
Aufbau Principle, Pauli Exclusion, Hund's Rule. JEE asks configuration of elements, or identifies exceptions (Cr, Cu).
Electronic Configuration Exceptions. JEE asks configuration of Cr or Cu, or explains stability.
Photoelectric Effect. JEE gives frequency or wavelength, asks KE or stopping potential.
Energy of Photon. JEE gives wavelength, asks energy in eV or J.
Ionization Energy and Spectral Transitions. JEE asks IE for H-like species, or compares IE of different atoms.
Calculating Wavelength from Energy Difference. JEE gives transition, asks wavelength in nm or Å.
Rydberg Constant and Its Units. JEE gives R_H value, asks to calculate wavelength.
Bohr's Model Limitations. JEE asks limitations of Bohr model in conceptual questions.
Electromagnetic Spectrum Regions. JEE asks which region a given wavelength belongs to.
Energy Conversion: eV to Joules. JEE often requires conversion in numerical problems.

Common traps

Confusing atomic number with mass number; Z defines element identity. Atomic Number (Z) & Mass Number (A)
Using $E_{n}$ formula for multi-electron atoms; it's only for H-like species. Bohr's Model of Hydrogen Atom
Forgetting to square Z; using Z instead of Z^2. Energy of Electron in H-like Atom
Using formula for hydrogen (Z=1) for other species without adjusting Z. Radius of Bohr Orbit
Using formula for hydrogen only; Z must be included. Velocity of Electron in Bohr Orbit
Using n1 > n2; n1 is lower energy level, n2 is higher. Wavelength of Emitted Photon (Rydberg Formula)
Confusing Balmer (visible) with Lyman (UV). Spectral Series of Hydrogen
Using formula for transitions to a specific level; it's for all possible downward transitions. Calculating Number of Spectral Lines
Forgetting that h is Planck's constant; using wrong units. de Broglie Wavelength
Using $\frac{h}{2 π}$ instead of $\frac{h}{4 π}$ . Heisenberg Uncertainty Principle
Forgetting that l can be 0,1,2,...n-1; not up to n. Quantum Numbers
Thinking all p orbitals are same shape; they are oriented differently. Shapes of Orbitals
Confusing angular and radial nodes; angular nodes depend on l. Number of Nodes
Forgetting that 4s fills before 3d, yet in transition-metal cations the 4s electrons are lost first (3d is lower in energy once occupied). Aufbau Principle, Pauli Exclusion, Hund's Rule

Topics in Atomic Structure

Bohr's Model
Quantum Numbers
Atomic Orbitals
Electronic Configuration
Dual Nature and de Broglie
Heisenberg Uncertainty Principle

Previous-year questions on Atomic Structure

JEEGenie has 373 previous-year questions on Atomic Structure. A few worked examples follow.

Year	Questions
2026	26
2025	21
2024	25
2023	29
2022	26
2021	27
2020	15
2019	36
2018	3
2017	12
2016	4
2015	3
2014	3
2013	8
2012	4
2011	4
2010	8
2009	3
2008	2
2007	1
2006	4
2005	5
2004	7
2003	6
2002	4
2001	3
2000	5
1999	3
1998	4
1997	6
1996	6
1995	1
1994	1
1993	7
1992	2
1990	2
1989	5
1988	6
1986	6
1985	5
1984	9
1983	7
1982	5
1981	3
1979	1

Question 1 easy

What is the energy (in J atom−1) required for the following process? Li2+ (g)

\to

Li3+ (g) + e− (Take the ionization energy for the H atom in the ground state as

2.18 \times 10^{- 18} {J atom}^{- 1}

)

$8.72 \times 10^{- 18}$
$1.962 \times 10^{- 18}$
$1.962 \times 10^{- 17}$
$6.54 \times 10^{- 17}$

Answer: C

Explanation. For the hydrogen-like ion

L i^{2 +}

, the nuclear charge is

Z = 3

. The ionization energy for a hydrogen-like species in its ground state is given by:

I E = Z^{2} \times I E_{H}

Substituting

Z = 3

and

I E_{H} = 2.18 \times 10^{- 18} {J atom}^{- 1}

I E = (3)^{2} \times (2.18 \times 10^{- 18}) = 9 \times 2.18 \times 10^{- 18}

I E = 19.62 \times 10^{- 18} = 1.962 \times 10^{- 17} {J atom}^{- 1}

This is the energy required to remove the last electron from

L i^{2 +}

C) 1.962 \times 10^{- 17} {J atom}^{- 1}

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 1

Question 2 medium

Which of the following statements are correct, if the threshold frequency of caesium is

5.16 \times 10^{14} H z

? A. When Cs is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on Cs , the ammeter shows the presence of current. B. When the brightness of the yellow light is dimmed, the value of the current in the ammeter is reduced. C. When a red light is used instead of the yellow light, the current produced is higher with respect to the yellow light. D. When a blue light is used, the ammeter shows the formation of current. E. When a white light is used. the ammeter shows formation of current. Choose the correct answer from the options given below:

B, C and D Only
A, C, D and E Only
A, B, D and E Only
A, D and E Only

Answer: C

Explanation. The threshold frequency of caesium is

5.16 \times 10^{14}

Hz, which corresponds to yellow light. Since yellow light is at the threshold, it can just barely cause photoemission, so statement A is correct. Dimming the light reduces the number of photons, thus reducing the current, making B correct. Red light has a lower frequency than yellow, so it cannot produce photoelectrons, making C incorrect. Blue and white light have higher frequencies than yellow, so they can produce current, making D and E correct. Therefore, the correct statements are A, B, D, and E, which corresponds to option C.

From NTA/IIT papers: JEE Main 2025 · 7 Apr Shift 1

Question 3 hard

According to Bohr's model, the highest kinetic energy is associated with the electron in the

first orbit of H atom
first orbit of He $^{+}$
second orbit of He $^{+}$
second orbit of Li $^{2 +}$

Answer: B

Explanation. For hydrogen-like atoms, the kinetic energy of the electron in the

n

-th orbit is

K E = \frac{1}{2} m v^{2} = \frac{Z^{2} e^{4} m}{8 ε_{0}^{2} h^{2} n^{2}} \propto \frac{Z^{2}}{n^{2}} .

Thus, higher

Z

and smaller

n

give larger kinetic energy. Compare the options: - A) H,

Z = 1

n = 1

\frac{Z^{2}}{n^{2}} = 1

- B) He

^{+}

Z = 2

n = 1

\frac{Z^{2}}{n^{2}} = 4

- C) He

^{+}

Z = 2

n = 2

\frac{Z^{2}}{n^{2}} = 1

- D) Li

^{2 +}

Z = 3

n = 2

\frac{Z^{2}}{n^{2}} = \frac{9}{4} = 2.25

The largest value is

4

, which corresponds to the first orbit of He

^{+}

{B) first orbit of He}^{+}

From NTA/IIT papers: JEE Advanced 2024

Question 4 easy

The wavelength of an electron of kinetic energy

4.50 \times 10^{- 29}

J is _________

\times 10^{- 5}

m. (Nearest integer) Given : mass of electron is

9 \times 10^{- 31}

kg, h

= 6.6 \times 10^{- 34}

J s

Answer: 7

Explanation. We use the de Broglie wavelength formula:

λ = \frac{h}{p}

where

p

is the momentum. The kinetic energy is

K = \frac{p^{2}}{2 m}

p = \sqrt{2 m K}

Thus,

λ = \frac{h}{\sqrt{2 m K}}

Given:

h = 6.6 \times 10^{- 34} J s

m = 9 \times 10^{- 31} kg

K = 4.50 \times 10^{- 29} J

First calculate

2 m K

2 m K = 2 \times 9 \times 10^{- 31} \times 4.50 \times 10^{- 29}

= 18 \times 4.50 \times 10^{- 60}

= 81 \times 10^{- 60}

= 8.1 \times 10^{- 59}

Now take the square root:

\sqrt{2 m K} = \sqrt{8.1 \times 10^{- 59}}

= \sqrt{8.1} \times 10^{- 29.5}

Since

\sqrt{8.1} \approx 2.846

we get

\sqrt{2 m K} \approx 2.846 \times 10^{- 29.5}

Now compute

λ

λ = \frac{6.6 \times 10^{- 34}}{2.846 \times 10^{- 29.5}}

= \frac{6.6}{2.846} \times 10^{- 34 + 29.5}

\approx 2.319 \times 10^{- 4.5}

Write

10^{- 4.5} = 10^{- 5} \times 10^{0.5}

λ \approx 2.319 \times 10^{0.5} \times 10^{- 5}

Since

10^{0.5} = \sqrt{10} \approx 3.162

λ \approx 2.319 \times 3.162 \times 10^{- 5}

\approx 7.33 \times 10^{- 5} m

To the nearest integer in the given form,

λ \approx 7 \times 10^{- 5} m

Final answer: **7.0**

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 1

Question 5 medium

The wavelength of an electron and a neutron will become equal when the velocity of the electron is

x

times the velocity of neutron. The value of

x

is ____________. (Nearest Integer) (Mass of electron is

9.1 \times 10^{- 31} k g

and mass of neutron is

1.6 \times 10^{- 27} k g

)

Answer: 1758

Explanation. The de Broglie wavelength is

λ = \frac{h}{m v}

. For the electron and the neutron to have equal wavelengths:

\frac{h}{m_{e} v_{e}} = \frac{h}{m_{n} v_{n}} \Rightarrow m_{e} v_{e} = m_{n} v_{n} .

So the two particles must have equal momenta, which gives

x = \frac{v_{e}}{v_{n}} = \frac{m_{n}}{m_{e}} .

Substitute the masses:

x = \frac{1.6 \times 10^{- 27}}{9.1 \times 10^{- 31}} = \frac{1.6}{9.1} \times 10^{4} = 0.17582 \times 10^{4} = 1758.2.

The nearest integer is 1758. The electron is about 1758 times lighter than the neutron, so it must move about 1758 times faster to have the same momentum and hence the same wavelength. Answer: 1758

From NTA/IIT papers: JEE Main 2022 · 26 Jul Shift 1

Frequently asked questions

How much of JEE Main comes from Atomic Structure?: JEEGenie estimates about 3% of JEE Main marks come from Atomic Structure, based on recent papers. The share varies from year to year.
Which formulas matter most in Atomic Structure?: The Atomic Structure sheet on this page has 16 formula entries, starting with Atomic Number (Z) & Mass Number (A), Bohr's Model of Hydrogen Atom, Energy of Electron in H-like Atom, Radius of Bohr Orbit, Velocity of Electron in Bohr Orbit. Each one comes with when to use it and the trap to avoid.
What topics does Atomic Structure cover for JEE?: Atomic Structure covers Bohr's Model, Quantum Numbers, Atomic Orbitals, Electronic Configuration, Dual Nature and de Broglie, Heisenberg Uncertainty Principle.
How should I revise Atomic Structure before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Atomic Structure questions on JEEGenie.
How many previous-year questions are there on Atomic Structure?: JEEGenie has 373 previous-year questions on Atomic Structure, and this page shows a few with worked explanations.
Is practice on Atomic Structure free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.