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Class 11 chemistry · linked to Structure of atom · Conceptual practice

Source: CBSE Class 11 chemistry practical syllabus · use your school laboratory manual (NCERT Lab Manual where your school uses it).

Electron shells and quantum numbers (Class 11 chemistry practical)

You walk through how electrons fill shells and how four quantum numbers label an electron.

There is no titre to copy. The “result” is the configuration and quantum-number set you write for the atoms your teacher assigns.

Published practice page. Concentrations, masses, and numerical answers come from your school laboratory manual and your own readings — not invented here. Not yet reviewed by a named chemistry reviewer. Version 1.0.0, updated 2026-10-03.

Safety — read before you start

Safety warning. Practise here. Perform the real experiment only in your school lab, with your teacher present.

  • This page is conceptual. Any live discharge-tube or spectrum demo is hazardous — teacher-supervised only.

Wear: Lab coat, Splash goggles, Gloves, as your teacher directs.

Follow your teacher’s disposal instructions. Do not pour leftovers down a household drain.

Loads only after you tap. Click glowing shell rings to fill them; drag to orbit. Falls back to a flat diagram if WebGL is unavailable.

Aim

To practise writing electronic configurations and assigning quantum numbers for atoms and ions chosen by your teacher, using Aufbau, Pauli, and Hund’s rules.

Methods and quantities can differ between schools. Follow your teacher's instructions.

Apparatus and chemicals

Apparatus and chemicals
ItemNote
Periodic table (school copy)Use the table your teacher provides.
Notebook and pencilWrite configs before you check them.
Optional orbit / shell diagramOnly if your lab has one. This page’s diagram is a schematic.
None for the conceptual drill (none)If your school pairs this with a discharge-tube demo, follow teacher and lab-manual safety only.

Picture guide

Simple atom model showing nucleus and electron shells
Shells are energy levels around the nucleus. Fill K first, then L. This picture is not to scale — use it only to practise the order.

Theory and reaction

Open

n labels the shell. l labels the subshell (0 = s, 1 = p, 2 = d, 3 = f). mₗ labels orientation. mₛ is spin ±½.

Pauli: no two electrons share all four quantum numbers. Hund: fill parallel spins in a subshell before pairing.

Cr and Cu are the usual exceptions you are expected to recall. Do not invent others.

Bohr: m v r = n h / 2 pi. Photon: E = h nu.

Procedure

  1. From your teacher’s list, pick the first atom or ion. Write Z and the number of electrons.
  2. Fill orbitals in Aufbau order. Apply Hund in open subshells. Mark Cr/Cu-style exceptions if they appear.
  3. For one valence electron your teacher names, write n, l, mₗ, mₛ.
  4. Compare with a partner or the teacher’s key. Fix mistakes before the next species.
  5. If a spectrum demo is shown, note only what you actually see. Do not invent wavelengths.

Observation table

Enter the readings from your school lab in the practical file below. This page does not fill them in for you.

Type the readings in your practical file

Calculation

No numerical titre. Check that electron count matches Z (or Z ± charge) and that Pauli is not broken.

Result

List the configurations and quantum-number sets you wrote for the species assigned in class. Leave blanks where you were not assigned work.

Precautions

  • Do not copy a full answer key into your practical file if your teacher wants your own work.
  • Treat demo tubes and high-voltage kit as teacher-only equipment.

Viva questions

Answer one question at a time. The full answers stay closed until you open them.

Question 1 of 3

What does the principal quantum number n tell you?

Answer choices

Pick an answer first.

Show all questions and answers

  1. What does the principal quantum number n tell you?

    Answer: Shell / main energy level. Reason: n indexes the shell and sets the broad energy and size scale.

  2. Hund’s rule says you should…

    Answer: Fill parallel spins across a subshell before pairing. Reason: Maximise unpaired parallel spins in a subshell before pairing.

  3. Which set is a common exam exception?

    Answer: Cr and Cu configurations. Reason: Cr and Cu prefer half-filled / filled d patterns.

Common mistakes

  • Writing 4s after 3d for the filling order of K/Ca without checking Aufbau.
  • Giving two electrons the same four quantum numbers.
  • Inventing line wavelengths or energy values not measured or printed in your manual.

Frequently asked questions

Can I do this at home?
No. Use this page to practise the order of ideas and steps. Do the real experiment only in your school laboratory, with your teacher present.
Is this an official CBSE practical title?
It is a practice lab linked to the Structure of atom note. Your school’s official practical list may use different titles — follow that list for records.

Your practical file

Name, school, and roll number are optional and are not sent anywhere.

The practical file opens on this device.

Review

Not yet reviewed by a named chemistry reviewer. Published for practice only — follow your teacher and laboratory manual for quantities and safety.

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Related notes

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