Are these Atoms notes free?

Yes. The full 4-page Atoms sheet is free inside CapCompass, which runs in your browser with no account needed.

What does the Atoms revision sheet cover?

Alpha-particle scattering, what it showed, One alpha: impact parameter and closest approach, closest approach, head-on: all its K becomes potential energy, aimed head-on, b = 0, aimed far off, large b, Thomson's model vs Rutherford's model, Thomson, Rutherford, Bohr's postulates, the fix, Why an orbit is stable, Radius and energy of the nth orbit, radius, hydrogen-like atom of atomic number Z.

Is this for Class 12 CBSE Physics?

It is written from the NCERT syllabus, so it serves CBSE and any board that follows NCERT for Physics.

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Atoms — Class 12 CBSE Physics revision notes

A 4-page visual revision sheet for Atoms, written for Class 12 CBSE Physics. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.

Atoms revision notes, page 1 of 4 — A preview of page 1 — all 4 pages open full size in the app.

Atoms in one look

Rutherford found the nucleus, Bohr made it stable, hydrogen's spectrum proved him right

Alpha-particle scattering, what it showed

alpha particles (charge +2e) fired at a thin gold foil, a detector swung round it
most passed straight through, undeflected: the atom is mostly empty space
a small fraction scattered through large angles, a very few bounced almost straight back
large-angle scattering meant a small, massive, positively charged core doing the repelling: the nucleus

One alpha: impact parameter and closest approach

closest approach, head-on: all its K becomes potential energy d=2 Z e^2/4πε_0 K
aimed head-on, b = 0 θ=180°
aimed far off, large b θ≈0

Thomson's model vs Rutherford's model

Thomson

positive charge spread through the whole atom
electrons embedded in it, like fruit in a pudding
predicts only small deflections, never a large one

Rutherford

positive charge concentrated in a tiny central nucleus
electrons revolve at a distance, around mostly empty space
explains large-angle scattering, close approaches to the concentrated charge

Page 1 of 4. The full sheet, all 4 pages, opens free in the app.

What this Atoms sheet covers

Alpha-particle scattering, what it showed
One alpha: impact parameter and closest approach
closest approach, head-on: all its K becomes potential energy
aimed head-on, b = 0
aimed far off, large b
Thomson's model vs Rutherford's model
Thomson
Rutherford
Bohr's postulates, the fix
Why an orbit is stable
Radius and energy of the nth orbit
radius, hydrogen-like atom of atomic number Z
energy
ground state of hydrogen
Energy falls off fast with n
gap between adjacent levels, large n
The hydrogen spectrum, series by series
Rydberg formula
wave number of an emitted line
Rydberg constant
Symbols
X-rays: the tube, the spectrum, Moseley
Collisions of electrons with atoms
Traps that cost marks
Tricks that save time

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