Electron was discovered during experiments on the discharge of electricity through rarified gases. The magnitude of electric charge (e) was determined by Millikan. Charge of the electron = 1.602 X10 -19 coulomb
Bohr Model of the Atom:
Proposed by Neil Bohr in 1913. Bohr applied the Planck’s quantum theory to the Rutherford nuclear atom with remarkable success.
An atom consists of a positively charged nucleus at the centre. The electrons move round the nucleus in certain stationary orbits of definite radii and not all possible radii.
The radius of the orbit is such that the angular momentum of the electron is an integral multiple of h/2p.
Electron may jump from one orbit to the other, in which case the difference in energy between the two states of motion is radiated in the form of a light quantum.
Invisible electromagnetic radiations, Wavelengths range form 0.010A – 100A. These are discovered by Roentgen. When a fast moving electron is suddenly stopped a part of its kinetic energy is converted into X-ray photon the rest of the energy is converted into heat.
Wave Particle Duality:
To understand any given experiment, we must use either the wave or the photon theory, but not both. Light sometimes behaves like a wave and some times like a particle
de Broglie Hypothesis:
Photons are treated as “packets of light” behaving like a particle. Momentum of a photon: p = E / c = h/l Energy of a photon: E = hc/l
Heisenberg Uncertainty Principle:
If position is identified the momentum cannot be measured. If momentum is measured the position is lost. Dx X Dp ³ h / 4π
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"Title" Tutorial Summary :
Atomic physics deals with the structure and behavior of the atom. One of the most elementary and important parts of the atom is the electron. It was discovered in 1897 by J. J. Thomson. The behavior of these electrons, and thus the whole atom itself, was described by the Bohr theory of the atom. This said the electrons occupy certain discrete, quantized orbits. They cannot occupy the areas in between the set orbits. This unusual explanation explains atomic spectra observations very well. Another important aspect of atomic structure is the wave particle duality. Sometimes light can behave as a wave, other times as a particle. The same can be said of matter. Louis deBroglie explained how particles can have wave attributes like a wavelength. These ideas, along with other contributions, helped explain the structure of the atom.
Specific Tutorial Features:
• Animations of the discovery of electrons, the Bohr model of the atom, and electron transitions.
• Concept map showing inter-connections of new concepts in this tutorial and those previously introduced.
• Definition slides introduce terms as they are needed.
• Visual representation of concepts
• Animated examples—worked out step by step
• A concise summary is given at the conclusion of the tutorial.
"Title" Topic List:
The discovery of electrons
The Bohr model of the atom
Radii and energy level values