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Disccovery of the Electron, Models & Theories

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Aditi Singh

on 30 September 2014

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Transcript of Disccovery of the Electron, Models & Theories

- proved that electron waves could only exist
at specific frequencies
- According to the relationship E = hv, these
frequencies corresponded to specific energies
- investigations proved that electrons, like
light waves, can be bent, or diffracted
- Diffraction experiments showed that electron
beams, like waves, can interfere with each
Did several experiments to conclude:
1) Negative charges came within the atom
2) The atom was divisible
3) Atoms contained both negative and positive particles

JJ Thompson
Discovery of the Electron, Models & Theories
He discovered that electrons are very small but contain lots of charge (1.60 x 10 -19 C)
Calculated the mass of an electron using the charge and Thomson’s charge-to-mass ratio

Robert Milikan:
Danish Physicist, 1885-1962)
Proposed a model of the hydrogen atom : the nucleus is orbited by electrons, which are in different energy levels.
Explained H-Line Emission Spectrum:
Further out- Higher energy
There are no electrons in between energy levels.
Electrons can jump energy levels and when they do, they absorb or emit light energy

Neils Bohr
French Scientist , 1892-1987
Discovered that quantized electrons act like waves
Electrons are waves confined to the space around the nucleus with specific f and E.
Electron beam can be diffracted.

Louis de Broglie:
Important Experiments
Theories Through Time
Discovered it's not possible to determine the position and velocity of an electron at the same time.
Developed uncertainty principle

Werner Heisenberg
Erwin Schrodinger
- Develops mathematical equations to describe electron motion
- Clouds represent the region with the
highest possibility of finding electrons.
- Develops an equation that treats
electrons as waves.

Bohr Model of the
Hydrogen Atom (1913)

modification of the Rutherford model of 1911
- positively charged nucleus is surrounded by negatively-
charged electrons that orbit the nucleus only in orbits
atom is held together by electrostatic forces between the positive
nucleus and the negative surroundings
when electrons are in the orbit closest to the nucleus, the hydrogen
atom is in its lowest energy state
when the electron is in the outermost orbit, the atom has the highest
potential energy

- electrons absorb light photons when they move to a higher state of
energy and emit light photons when they jump to a lower energy

Quantum Model
Saanchi Shah
Aditi Singh
Arjun Patel
Abishek Mankar
Jay Patel
Madhu Sivaraj

- Based off mathematics and uses orbitals: shapes that define a
volume of space where there might be an electron
Uncertainty Principle: no one can never know the exact location and
momentum of an atom’s electron at the same time
-Erwin Schrödinger devised an equation that considers electrons as waves.
Quantum numbers are used to describe orbitals in an atom.

Principal quantum number:


it describes the main energy level
Angular momentum quantum number:

it describes the shape of the orbital
Magnetic quantum number:


describes the orientation of
the orbital about the nucleus.
Spin quantum number:
indicates the spin state of the
electron in the orbital

Robert Milikan finds the measurement of
electron charge (1913)
Louis de Broglie
Broglie's discovery in wave mechanics added on to the Bohr model showing the wave nature of electrons. (1924)
Werner Hiesenburg

Hiesenberg calculates the behavior of electrons and subatomic particles (1925)
Erwin Schrondinger introduces the quantum mechanical model by adding on to the Bohr model (1926)

Hiesenburg noticed behaviors in the electrons that make them alike, and also looked at the path in which they orbit the atomic nucleus.
- Theories have held up over time and added to previous models to improve our understanding.
- Theories are never completely rejected however certain parts of them are still in use today
-The basic structure of the atom (spherical, with positive particles surrounded by negative) has remained consistent with time.
- Theories helped the future scientists advance
their research on atoms
Models and Theories in the Timeline of History
JJ Thompson

- He calculated the energies that an
electron would have in the energy levels for
the hydrogen atom
- used these values to mathematically show
how the various spectral series of hydrogen
atoms were produced
- Bohr’s calculated values agreed with the experimentally observed values
-This model led scientists to conclude
that a similar model could be
applied to all atoms

- Performed oil drop experiments
- Used the mass of the drop and the charge on the plates, to calculate the charge on an electron

Famous experiment
"Schrodinger's Cat"
Robert Milikan
Louis Broglie

English Scientist, 1856- 1940
American Physicist, 1868- 1953
German Physicist, 1901-1976
- studied the path of an electric
current through a gas in a device called
a cathode ray tube.
- series of 2 experiments
- Metals at one end of a tube produced
a beam and a “glow” at other end of
tube on a fluorescent screen
Neils Bohr
Earlier Theories
335 BC: Aristotle teaches that all substances
are made up of 4 elements
465 BC: Democritus adopts his mentors atomic theory and creates a detailed hypothesis.
1910: Rutherford model created
Milikan and Bohr
Neils introduces the Rutherford-Bohr Model which depicts atom as a positive nucleus surrounded
by electrons in orbit in "energy levels"
JJ Thomson discovered the electron(1897) and that atoms are divisible. He reaches the conclusion that atoms contain positive centers and negative particles around it.
JJ Thomson
This discovery leads to the Plumb Pudding Model of the atom(1904) which added the electron to the previous understanding of atoms
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