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Development of the Atomic Theory


Mimi Xayaphone

on 2 November 2014

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Transcript of Development of the Atomic Theory

Democritus was a Greek philosopher who first developed the idea of atoms. He believed that all matter consists of indivisible particles, called "atomos", that moves around in a void.
All matter consists of atoms.

Atoms are indivisible.

Atoms have different sizes and shape

Atoms have different properties

Atoms are in constant motion in a void, and collide with each other in which they join together.
Democritus thought that if a rock can be split in half, then those half can be split again, and again until...... can not be divided anymore leaving us with an atom!
Erwin Schroedinger
R.A. Milliken
Oil Drop Experiment

460 BC- 370 BC
Niels Bohr
Democritus's Theory
October 7, 1885- November 18, 1962
Niels Bohr was a Danish scientist who also contributed to the development of the atomic structure. Bohr used the ideas and theory of other scientist to come up with the Bohr Energy Level Model. Bohr carried out experiments with light to expand and correct Rutherford's Planetery Model. He also applied quantum mechanics to propose his theory.
Bohr's model of the atom was based on observations of the hydrogen atom. He observed the atomic emission spectrum of hydrogen. Bohr concluded that electrons orbit around the nucleus at a fixed distance and at the speed of light. He also proposed the idea that electrons can travel in between levels but they must absorb or emit a certain amount of energy.
Bohr's Energy Level Model
Bohr's atomic model depicts the electrons orbiting the nucleus in a path at a fixed distance.
Werner K. Heisemburg
John Dalton
September 6, 1766- July 27, 1844
John Dalton was an English chemist credited with being the "Father of the Atomic Theory". He developed 5 postulates and the three Atomic Laws.
Dalton's Postulates

All matter is made up of extremely small particles called atoms.

All atoms of a given element have identical size, mass, and chemical properties.

All atoms of different elements are different.

Atoms cannot be created, divided, or destroyed

A chemical reaction is a rearrangement, seperation, or attachment of atoms.

Dalton's Atomic Laws

1. Law of Conservation of Mass: Matter cannot be created or destroyed physically or chemically.

2. Law of Constant Composition: Ratio of atoms is constant when atoms join to form molecules.
EX: NO2 (Nitrogen Dioxide) have twice as many oxygen atoms as nitrogen

3. Law of Multiple Proportions: If two elements can combine to form a compound, then ratio of sencond element combined with a fixed mass of the first element is always a ratio of small whole numbers.
JJ Thomson
Ernest Rutherford
August 30, 1871- October 19, 1937
Max Planck
JJ Thomson was an English physicist who first offered experimental evidence that contradicts the theory of atoms being indivisible. He carried on an experiment with cathode rays leading to the discovery of electrons.
Thomson's Experiment and Model
Ernest Rutherford was a student of JJ Thomson. In 1911, Rutherford conducted the Gold Foil experiment to test out the Plum Pudding Model. He experimented by directing a beam of alpha particles at a thin piece of gold foil. He discovers that the alpha particle deflected back occasionally because the particle was repelled when it hit the positive charge center.
Important Contributions
Abdera, Greece
Manchester, UK
Copenhagen, Denmark
Morrison, IL
Atomic Structure History
By: Mimi Xayaphone
Period: 2

Cumberland, England
December 18, 1856- August 30, 1940
Brightwater, New Zealand
Gold Foil Experiment
Cathode Ray Tube
11:59 PM
Wed, October 8
New Message
Thomson used the cathode ray tube (ctr) in his experiments. He put the tube in a magnetic field and disovered that the cathode ray bends. The path of the ray curved away from the negatively charged plate and toward a positively charged plate. This led him to conclude that the charged particles consists of electrons since "likes repel" and "opposites attract".
Thomson created the Plum Pudding model. The model consists of a positively charged sphere and smaller electrons dispersed to maintain a neutral charge.

Rutherford's experiment concluded that:
Atoms contain a positively charged center or "nucleus" , and that the electrons surround the nucleus at a distance.
The atom is an empty space with a tiny, extremely dense nucleus in the center.
March 22, 1868- December 19, 1953
Milliken was an American physicist, best known for measuring the charge of a single electron.
Milliken performed a series of experiments to determine the charge of an electron. His most famous experiment the Oil Drop experiment. He sprayed charged drops of oil and let it suspend between two charged plates that are parallel to each other. The electric field was applied and the free fall of the drops was stopped.
Würzburg, Germany
December 5, 1901- February 1, 1976
Werner Heisemburg was a German physicist who contributed to the quantum theory. Instead of using physical models to work out the problems of an atom, he worked with experimental data and mathematical results. Heisenburg developed the matrix mechanics formulation of quantum mechanics. The matrix mechanics formulation was the application of mathematical systems to atomic science.
Vienna, Austria
August 12, 1887 -January 4, 1961
Schroedinger was an Austrian physicist who expanded on the Bohr model of the atom. He discovered that electrons can be considered as waves and particles.
Kiel, Germany
April 23, 1858- October 4, 1947
Max Planck was a German physicist who originated the quantum theory. Planck proposed that energy is radiated every minute and in separate quantized amounts. His theory was used later by scientists such as Niels Bohr to create a new model of the atom.
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