This document provides a timeline of important figures in the development of atomic theory from Democritus in 460-370 BC to Werner Heisenberg in the 1920s. It summarizes their key contributions, including Democritus' original concept of atoms, Dalton introducing the idea of different types of atoms, J.J. Thompson discovering electrons and proving atoms are divisible, Rutherford discovering the nucleus, Bohr proposing electron energy levels, and Heisenberg establishing the uncertainty principle in quantum mechanics.

1. Atomic Timeline
By: Lyndsey Benes And Jacqueline Patel

2. Democritus
• Lived from 460-370BC
• Came up with the word atomos.- lter became called the atom.
• Theory was mainly about atoms being in the atmosphere
• There are certain atoms for solids and certain atoms for liquids
• Atoms are individually created and cannot be separated.
• Sizes can differ according to the influences on them.
• Atoms cannot be split no matter their size
• It is thought of the atom was based off of the analogies from the human senses.
• All things are made of atoms, the atoms could not prove them with scientific
experiment.

3. Aristotle
• 384-322BC
• Believed that if you keep cutting up pieces of a matter it is always going to
be made up of that same thing.
• Didn’t believe that atoms could be different sizes.
• Believed that the heavens were made up of a fifth element called a aither
• His theory had two forces, conflict and harmony
• That was his most popular theory.

4. John Dalton
• Atom was a ball
• A gas consists of individual particles
• Each element has its own atom
• Introduced compounds
• Measured the mass of elements that combined when compounds formed
• His discovery lead to the atomic theory in 1803
• Discovered colorblindness, and suffered from it.
• Studied metrology.

5. J.J. Thompson
• Discovered isotopes
• Discovered that atoms were made up of smaller particles.
• Won the nobel prize in physics
• Discovered ray tubes and cathode tubes
• Estimated the mass of the ray by measuring the heat generated by the ray
when they hit the junction and comparing it with the reflection of the rays.
• Concluded that the rays were made of negatively charged
particles(electrons)- he called them corpuscles- later electrons was
suggested be Goerge Stoney.
• Concluded that atoms were divisible and made of particles.
• Plum Pudding model

6. Ernest Rutherford
• Completed the gold foil experiment, which he thought would be proof that
J.J Thompson’s plum pudding model was correct, but it proved that his
model was wrong.
• Discovered that the thing in the middle of an atom was called the nucleus.
• Discovered the neutron
• Discovered the atomic bomb
• After his experiment people started to realize that atoms were made up of
sub-atomic particles.
• Discovered all of the atoms nuclear charge is in the nucleus.

7. James Chadwick
• Discovered the neutron with Rutherford.
• Discovered that the unknown particles were in the nucleus
• This has been know as the neutron because is had no charge
• his discovery of the neutron became essential to the understanding of the
nuclear fussium of uranium 233.
• Nobel Prize in Physics
• Got the Franklin Medal
• Got the Hughes Medal

8. Erwin Schrueinberg
• Physicist
• Found more proof of the quantum theory
• Electrons are on energy levels
• Discovered the wave configuration
• Started working in Berlin, Germany but had to escape because of Hitler.
• Worked with Max Planck.
• Figured out that an orbital can only hold 2 electrons
• Discovered the four main types of orbitals; S, P, D, F orbitals

9. Neils Bohr
Neils Bohr
• Believed that electrons existed on specific energy levels.
• Electrons moved in orbits around the nucleous
• Fixed distances apart
• Light is emmited when the electron becomes excited then comes back in
waves.

10. Louis De Broglie
• Proposed moving particles.
• Won the nobel prize in physics
• Thought that the electrons have dependencies similar to photons and that
electrons move in waves.
• Used Max Planck studies.
• Determined that both forms of energy existed in particles and wave lengths.

11. Werner Heisenberg
• Won the nobel prize in Physics.
• Created theory on Quantum Mechanics.
• In 1927 he published his “Uncertainty Principle”
• Made contributions to many different science branches.
• Helped plan the first West Germany Nuclear Reactor in Karlsruhe.
• President of the Germany Research Council. (GRC)