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Jan 1, 1000
Democritus
Democritus lived in the ancient Greek times probaby about 500 B.C. Democritus came up with the idea that all matter consisted of very small particles that can't be divided. He named these particles atoms. He also believed that there were different sets of properties. Democritus came up with these ideas through discourse. -
Jan 2, 1000
Aristotle
Aristotle lived in the ancient Greek times probably around 500 B.C. Aristotle did not believe the same thing that Democritus did. He believed that everything was made of fire,air, water, and earth. He also believed that there was no limit to the number of times something can be divided. Aristotle came up with these though discourse as well. -
Isaac Newton
Isaac Newton formulated a theory for light, and suggested that matter was made up of small, solid, impenetrable particles in motion. He also suggested that all atoms are held together by attractions, otherwise known as forces. -
John Dalton
Dalton concluded that matter consisted of individual particals that can't be divided. He found the evidence of atoms by measuring the masses of elements that combine to form compounds. The main points of Dalton's theory were;
1. All elements are made up of atoms.
2. All atoms in the same element have the same mass.
3. Compounds contain more than one type of atom.
4. In certain compounds, atoms of different elements always combine the same way.
Dalton also made wooden models of his atom theory. -
J.J. Thomson
Thomson hypothesised that the particles in matter were charged. He discovered this by sending an electrical current through a low pressured gas. A glowing beam appeared in the gas while there was a current going through it. He believed that the atoms in the gas were made up of smaller, charged particles. Thomson's experiment gave evidence that atoms were made of small particles that were charged. -
Pierre Curie
While working with his wife, Marie, Pierre Currie developed a way to find the mass of atoms. They were the first to use the term "radioactivity." The atomic mass could be used to detect particles in an atom. -
Hantaro Nagaoka
Hantaro Nagaoka rejected Thosmsons model because opposite charges are impenetrable. He suggested a new model in which a positively charged center is surrounded by a number of revolving electrons. Nagaoka used the work of J.J. Thomson to come up with his idea. However, his model was not accepted because it was incorrect. -
Ernest Rutherford
Rutherford believed that most particles would travel in a straight path from their source to a screen that lit up when struck. Those few that did not pass through, would be deflected slightly. Rutherford worked with Ernest Marsden to carry out an experiment. In this experiment they aimed a beam of alpha particles at a sheet of gold foil. When the beam hit the foil, few particles passed through, and most others were deflected. Through "The Gold Foil Experiment" the nucleus was discovered. -
Neils Bohr
Neils Bohr worked with Ernest Rutherford for a while on the atomic theory. This is why their models are alike in a lot of ways, except for the fact that Bohr's model focused mainly on the electrons in an atom. He believed that the electrons moved with constant speed in fixed orbits, and that the electrons could gain or loose energy when they moved between fixed energy levels. -
Erwin Schrödinger
Erwin Shrödinger developed mathematical equations to describe the way that electrons move in atoms. His work on this led to the electron cloud model. -
Ernest Marsden
Ernest Marsden was one of Ernest Rutherford's students. He helped Rutherford complete his model of the atom. He worked on "The Gold Foil Experiment" under Rutherford's supervision. -
James Chadwick
James Chadwick was led to believe that there were different particles in an atom's nucleus rather than electrons and protons. He was able to confirm the existence of neutrons in a nucleus by using a rather new way of detecting particles. Chadwick concluded that there were protons and neutrons in a nucleus. -
Louis de Broglie
Louis de Broglie suggested that the moving particles like electrons have properties like waves. He was able to come up with this through the work of Max Planck and Albert Einstein. Several years later, evidence was collected to supported his idea.
