Ch 12 - ATOMS12th Physics
Thomson's Plum Pudding Model
What was the fundamental structure of an atom according to J.J. Thomson's 1898 model, and what was its major failure?
What was the fundamental structure of an atom according to J.J. Thomson's 1898 model, and what was its major failure?
Structure: The atom is an electrically neutral, solid spherical cloud of uniformly distributed positive charge, with negatively charged electrons embedded within it like 'plums in a pudding'.
Failure: It completely failed to explain the origin of the discrete spectral lines (like the Balmer series) observed in atomic spectra. It also could not explain the large-angle scattering of alpha particles observed in later experiments.
Prism Memory Hook
A premium mnemonic for this topic is available in the Prism App.
Nature of Alpha Particles
What is the physical composition, mass, and charge of an alpha particle used in the Geiger-Marsden scattering experiment?
What is the physical composition, mass, and charge of an alpha particle used in the Geiger-Marsden scattering experiment?
Composition: It is essentially a Helium nucleus (a helium atom stripped of its two electrons).
Charge: It carries a positive charge of .
Mass: It has a mass roughly 4 times the mass of a proton (or hydrogen atom).
Context: Emitted spontaneously by radioactive elements like Bismuth-214, they possess high kinetic energy (e.g., ).
Prism Memory Hook
Alpha is a Double-Positive, Quad-Mass Helium Core.
Alpha-Particle Scattering Observations
What were the three critical statistical observations made by Geiger and Marsden when bombarding a thin gold foil with alpha particles?
What were the three critical statistical observations made by Geiger and Marsden when bombarding a thin gold foil with alpha particles?
Observation 1: The vast majority of alpha particles passed strictly straight through the gold foil without any deflection.
Observation 2: Only a small fraction (about ) scattered by angles greater than .
Observation 3: An extremely rare fraction (about ) experienced massive deflection, rebounding by angles greater than .
Prism Memory Hook
A premium mnemonic for this topic is available in the Prism App.
Also in this chapter
38 more cards to study in Prism
- 4Rutherford's Planetary Model of the Atom
- 5Distance of Closest Approach
- 6Assumptions of Rutherford Scattering
- 7Thomson vs. Rutherford: Average Scattering Angle
- 8Impact Parameter Formula
- 9Orbital Velocity in Rutherford Model
- 10Impact Parameter
- 11Total Energy of Revolving Electron
- 12Alpha Scattering on Solid Hydrogen
- 13Target Recoil in Rutherford Scattering
- 14Bohr's Second Postulate (Quantisation Condition)
- 15Bohr's Third Postulate (Frequency Condition)
- 16Radius of nth Bohr Orbit
- 17Failures of Rutherford's Model
- 18Total Energy of the nth Bohr Orbit
- 19Emission vs. Absorption Spectra
- 20Hydrogen Energy Levels in Electron-Volts
- 21The Five Hydrogen Spectral Series
- 22Bohr's First Postulate
- 23Rydberg Formula for Hydrogen Spectra
- 24De Broglie's Hypothesis & Bohr Orbits
- 25Standing Wave Condition for Orbits
- 26Kinetic vs. Potential Energy Ratio
- 27Number of Scattered Alpha Particles
- 28Positronium Ground State Energy
- 29Ground State and Ionisation Energy
- 30Scaling for Hydrogenic Ions
- 31Electric Current of a Revolving Electron
- 32Bohr's Correspondence Principle
- 33Limitations of the Bohr Model
- 34Mathematical Failure of the Bohr Model
- 35Reduced Mass & Isotope Shift
- 36Muonic Hydrogen Atom
- 37Inelastic Collision of Hydrogen Atoms
- 38Quantised Velocity in Bohr Orbits
- 39The Auger Process
- 40Time Period and Frequency of Revolution
- 41The Gravitational 'Atom'
Premium Chapter
12th Physics
The remaining 38 cards of Ch 12 - ATOMS are available in the Aspira Prism App with full interactive study tools, spaced repetition, and memory hooks.
Get Started with Prism