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

The Greeks The Key People: Leucippus and Democritus Plato Aristotle

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

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

The Four Elements

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

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

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

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

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.

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

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

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

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

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

Gold Foil Experiment

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”

The Bohr Model

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

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

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

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

Cross Section of the Large Hadron Collider (LHC)

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

Homework Reading: Section 1.3 Atomic Theory Pg 28-31