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Structure of the atom · परमाणु की संरचना

Electrons, protons, neutrons — count them for any of the first 20 elements and learn the three models.

Structure of the atom games

Inside the atom परमाणु की संरचना

ParticleChargeWhereDiscovered by
Electron (e⁻) इलेक्ट्रॉन−1shells around the nucleusJ. J. Thomson
Proton (p⁺) प्रोटॉन+1nucleusE. Goldstein (canal rays)
Neutron (n) न्यूट्रॉन0nucleusJames Chadwick, 1932

Atomic number Z = number of protons (= electrons in a neutral atom). Mass number A = protons + neutrons. So neutrons = A − Z. Example: sodium ²³Na, Z = 11 → 11 protons, 11 electrons, 12 neutrons.

Three models

Thomson: a positive sphere with electrons stuck in it, like a plum pudding. Rutherford (gold foil): most of the atom is empty; the positive charge and almost all the mass sit in a tiny nucleus. Bohr: electrons move in fixed shells (K, L, M, N) without losing energy; a shell holds at most 2n² electrons (2, 8, 18, 32).

Isotopes (समस्थानिक): same Z, different A — ¹²C and ¹⁴C. Isobars (समभारिक): same A, different Z — ⁴⁰Ca and ⁴⁰Ar. Also see electronic configuration and the periodic table.

Goes with NCERT Science Class 9, Chapter Structure of the Atom. Mass numbers are those of the most common isotope (chlorine: 35).

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A one-page chart to stick on the wall, and a worksheet to practise.

Structure of the atom

Inside the atom परमाणु की संरचना

ParticleChargeWhereDiscovered by
Electron (e⁻) इलेक्ट्रॉन−1shells around the nucleusJ. J. Thomson
Proton (p⁺) प्रोटॉन+1nucleusE. Goldstein (canal rays)
Neutron (n) न्यूट्रॉन0nucleusJames Chadwick, 1932

Atomic number Z = number of protons (= electrons in a neutral atom). Mass number A = protons + neutrons. So neutrons = A − Z. Example: sodium ²³Na, Z = 11 → 11 protons, 11 electrons, 12 neutrons.

Three models

Thomson: a positive sphere with electrons stuck in it, like a plum pudding. Rutherford (gold foil): most of the atom is empty; the positive charge and almost all the mass sit in a tiny nucleus. Bohr: electrons move in fixed shells (K, L, M, N) without losing energy; a shell holds at most 2n² electrons (2, 8, 18, 32).

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Structure of the atom — worksheet

Name: ____________________ Class: ______ Date: __________

1. Fill in for ²⁷Al (Z = 13): protons ____ electrons ____ neutrons ____
2. Who discovered the neutron? ________
3. Write two observations of Rutherford's gold foil experiment: ____________________
4. Maximum electrons in the M shell = ________
5. ¹²C and ¹⁴C are ________; ⁴⁰Ca and ⁴⁰Ar are ________
6. Draw the Bohr model of oxygen (Z = 8):
7.  

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