1. From Antiquity to Present: A Look at the History of the Atom

2. The Greeks
The Key People:
Leucippus and Democritus
Plato
Aristotle

3. Leucippus and Democritus
Both are considered the founders of the concept of atoms
They proposed that all matter was made up of small indivisible particles called “atomos”
Both argued that they were the primary reason change in the world occurred

4. Plato
Did not believe that small particles hitting each were responsible for the beauty found in the world
Believed that everything in the world was made up of four elements
Fire
Air
Water
Earth

5. The Four Elements

6. Aristotle
Supported Plato in stating that the four elements could not be made of atoms
Thought that they were continuous and could be infinitely divided
Aristotle’s view of atoms would be the dominant and “correct” until the 19th century

8. The Renaissance and Alchemy
The Key People:
Galileo
René Descartes
Pierre Gassendi

9. Galileo
Through his experiments, he found issues with Aristotle’s theories about particles
He tried to explain his results using the concept that small particles were the cornerstone of all matter

10. René Descartes Descartes promoted the concept of the atom
He differed in that he proposed that everything was made up of corpuscles
He also theorized that it was possible for them to be divided unlike the earlier proposed atoms

11. Pierre Gassendi
During this time, religion was a huge focus for everyone
Gassendi was a catholic priest that formed views to oppose Descartes
Tried to correct the atheistic philosophical ideas that Aristotle and others had provided.

12. Corpuscularianism Developed by Galileo and Descartes
Very similar to atom theory proposed by Leucippus and Democritus
The main differing point was that corpuscles could be divided while atoms were not
Remained popular during the Renaissance and support by famous people like Sir Isaac Newton

13. The Beginning The Key People: John Dalton J.J. Tomlinson
Ernest Rutherford
Niels Bohr

14. John Dalton Studied the gasses of out atmosphere
Based on his experimental results, he suggested that:
Matter is made up of small, hard spheres
Each element had its own unique small, hard spheres
Named these small, hard spheres atoms
Led to Dalton’s Atomic Theory

15. J.J. Tomlinson Studied electric currents in cathode ray tubes
Determined that the currents that he ran through the tubes were streams of negatively charged particles
Called them electrons and hypothesized that all atoms had to contain these particles
Led to the “raisin bun” or “plum pudding” model

16. Ernst Rutherford Wanted to find out what was inside the atom
Designed a famous experiment to find out what was inside the atom: the “Gold Foil Experiment”
He would go on to discover the nucleus, and later the two parts of the nucleus: the proton and the neutron

17. Gold Foil Experiment

18. Niels Bohr
Spent his time researching the area surround the nucleus which contained the electrons
He studied the light released by gas samples of atoms (like hydrogen) by running an electric current through them
As a result, he hypothesized that the electrons were organized around the nucleus in set energy “levels” or “shells”

19. The Bohr Model

20. The Future The Key People: Louis de Broglie Erwin Schrödinger
Werner Heisenberg

21. Wave-Particle Duality
Both de Broglie and Schrödinger heavily focused on the nature of the electron
Through their work, they established that electrons had characteristics of both waves and particles
Electrons have mass like particles but moves like a wave

22. Heisenberg’s Uncertainty Principle
Heisenberg took de Broglie and Schrödinger’s work towards establishing the wave-particle duality of electrons
His calculations helped determine that it was impossible to know both the position and the momentum of a particle
This effectively disproved Bohr’s model

23. Where We Are Today
We know that there are particles smaller than the electron
Lots of work is being done but they need huge facilities to do the experiments
Places include CERN in Switzerland and Fermilab in the US

24. Cross Section of the Large Hadron Collider (LHC)

26. Conclusion
We’ve moved from the Greek’s philosophical arguments about how the world worked and that the concept of the atom was first proposed
The Renaissance brought alchemy and the concept of Corpuscularianism
There was then a shift towards the atom again as new technologies helped establish the models we still use today
The future focuses on the concept of wave-particle duality and massive research areas

27. Homework
Reading: Section 1.3 Atomic Theory Pg 28-31