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Structure of Atom

Structure of AtomNEET Chemistry · Class 11 · NCERT Chapter 2

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4 interactive concept widgets for Structure of Atom. Drag any slider, change any number, and watch the formula and the answer update live. Built so you understand how each NEET problem actually works, not just the final number.

On this page

Bohr energy level diagram: transitions and spectral series
Quantum numbers validator (n, l, mₗ, mₛ)
Electron configuration builder with Aufbau and Hund's rule
Photoelectric effect visualizer (KE = hν − Φ)

Bohr's model and hydrogen spectrum

Click any two energy levels to see the photon energy, wavelength, and which spectral series (Lyman, Balmer, Paschen) the transition belongs to.

Bohr's model

Bohr energy level diagram: transitions and spectral series

Click any two energy levels to see the photon energy, wavelength, spectral series, and whether it is emission or absorption. All NEET-tested transitions are covered.

Energy levels

Energy (eV)n=1-13.60 eVn=2-3.40 eVn=3-1.51 eVn=4-0.85 eVn=5-0.54 eVn=6-0.38 eVn=7-0.28 eVemissionn=∞0 eV

Select transition

From n =

1
2
3
4
5
6
7

To n =

1
2
3
4
5
6
7

Type

Emission (photon released)

n=3 → n=2 (higher to lower)

Energy

ΔE = 1.889 eV

3.026e-19 J

Try this

  • The Balmer series (n=3→2, 4→2, 5→2) falls in visible light. Hα (n=3→2) = 656 nm (red).
  • All Lyman series lines (→ n=1) are in the UV region — that is why hydrogen discharge tubes emit UV strongly.
  • n=2→1 gives 121.6 nm (Lyman α). The formula: 1/λ = R_H × (1/n₁² - 1/n₂²), R_H = 1.097 × 10⁷ m⁻¹.

Quantum numbers and electron configuration

Validate any set of quantum numbers and see the orbital it describes. Then build the electron configuration for any element up to Kr, including Cr and Cu exceptions.

Quantum numbers

Quantum numbers validator

Enter any set of n, l, mₗ, mₛ to check whether it is physically valid, which orbital it describes, and how many electrons that subshell can hold.

1s electron (↑)
2p electron (mₗ=+1, ↓)
3d electron (mₗ=-2, ↑)
Invalid: l > n-1
Invalid: mₗ out of range

1, 2, 3, …

0 to n−1

−l to +l

mₛ (spin)

Valid set

3d

Electron in orbital 3d, mₗ = -2, spin ↑ (+½)

Subshell

3d

Orbitals in subshell

5 (mₗ = -2, -1, 0, 1, 2)

Max electrons

10 (subshell)

Orbital capacity

2 electrons

Try this

  • Try n=4, l=3 → 4f subshell. It has 7 orbitals (mₗ = −3 to +3) and holds 14 electrons.
  • The "invalid l > n-1" preset shows why the 2d subshell does not exist (it would require n=2, l=2).
  • NEET often asks: for n=3, how many orbitals exist? Answer: 9 (1 s + 3 p + 5 d = 9).
Electronic configuration

Electron configuration builder

Drag the slider to any element (Z=1–36) to see its full and noble-gas configuration, Aufbau filling sequence, and number of unpaired electrons. Exceptions (Cr, Cu) are flagged.

Fe

Z = 26

Full configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

Noble gas shorthand

[Ar] 4s² 3d⁶

Subshell filling (Aufbau order)

1s

2/2

2s

2/2

2p

6/6

3s

2/2

3p

6/6

4s

2/2

3d

6/10

Unpaired electrons (Hund's rule)

4

Try this

  • Slide to Cr (Z=24) and Cu (Z=29) — both are exceptions. Half-filled (3d⁵) and fully-filled (3d¹⁰) d orbitals are extra stable.
  • Fe (Z=26) has 4 unpaired electrons in 3d⁶ — each of the 5 d orbitals gets one electron first, then the 6th pairs up in one.
  • NEET often asks: which element has configuration [Ar] 3d⁵ 4s¹? Answer: Cr (atomic number 24).

Photoelectric effect and wave-particle duality

Explore Einstein's photoelectric equation KE = hν − Φ. Adjust frequency and metal to see whether electrons are ejected and how much kinetic energy they carry.

Photoelectric effect

Photoelectric effect visualizer

Choose a metal and slide the light frequency. See instantly whether ejection occurs, and watch Einstein's equation KE = hν − Φ update in real time.

Cesium
Potassium
Sodium
Zinc
Copper
Platinum

Sodium (Na)

Work function (Φ) = 2.75 eV · Threshold frequency ν₀ = 6.65 × 10¹⁴ Hz (451 nm, Visible)

Incident light frequency

ν = 10.0 × 10¹⁴ Hz

λ = 300.0 nm (UV)

Electron ejected

ν = 10.0 × 10¹⁴ Hz ≥ ν₀ = 6.65 × 10¹⁴ Hz

Einstein's equation: KE = hν − Φ

E(photon) = hν = 6.626e-34 × 10.0 × 10¹⁴ = 6.626e-19 J = 4.136 eV

Φ = 2.75 eV

KE = 4.136 − 2.75 = 1.386 eV = 2.220e-19 J

Kinetic energy of ejected electron

1.386 eV

2.220e-19 J

Try this

  • Try Sodium (Na) and slide frequency just above the threshold — KE jumps from 0 to a small positive value immediately.
  • NEET classic: increasing intensity of light below threshold still gives zero KE — frequency is what matters, not amplitude.
  • For Cu (Φ=4.7 eV), only UV light can eject electrons. Visible light (ν < 7.5 × 10¹⁴ Hz) cannot.

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