Physics · Class 12 · Chapter 12
Atoms
12 lessons104 min6 simulations10 practice questions
What is inside an atom, and why does hydrogen glow in a few sharp colours instead of a smooth rainbow? This chapter goes from Thomson's plum pudding to Rutherford's nucleus, found by firing alpha-particles at gold foil, and then to Bohr's hydrogen atom, whose three postulates give quantised orbits, energy levels En = −13.6 eV/n² and the line spectrum. De Broglie's standing waves explain Bohr's quantisation rule, and the chapter ends with what the Bohr model cannot do.
Also called: Bohr model · atomic physics · hydrogen spectrum
Lessons
12 lessons · 104 min
01Early models of the atomNCERT §12.17 min02Alpha-particle scatteringNCERT §12.210 min1 sim03Alpha-particle trajectoryNCERT §12.2, §12.2.110 min1 sim04Electron orbitsNCERT §12.2.27 min05Atomic spectraNCERT §12.36 min06Why Rutherford's atom failsNCERT §12.46 min07Bohr's postulatesNCERT §12.49 min1 sim08Energy levelsNCERT §12.4.19 min1 sim09Line spectra of hydrogenNCERT §12.510 min1 sim10De Broglie's explanationNCERT §12.610 min1 sim11Limits of the Bohr modelNCERT §12.66 min12Chapter reviewMust-know facts, traps and formulas14 min
Simulations
6 in this chapter
Counting alpha-particles behind the foilIn: Alpha-particle scatteringAlpha-particle scatteringIn: Alpha-particle trajectoryBohr orbits: how r, v and E scale with n and ZIn: Bohr's postulatesElectrons into hydrogen: which lines light up?In: Energy levelsHydrogen's line spectrumIn: Line spectra of hydrogenDe Broglie's wave round an orbitIn: De Broglie's explanation