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450 BCE
Democritus atomic model
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450 BCE
Democritus
He began the research to describe matter. He was the first to question if matter could be split into smaller and smaller parts to find the smallest possible piece. He believed that the smallest possible piece of matter was indivisible. He was the one who gave this smallest piece the name atom. The definition of this word being “not to be cut.” To Democritus, atoms were small, hard particles that were all made of the same material. He also thought that were formed into different shapes and sizes. -
Period: 400 BCE to
400 BC - 21ST Century
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375 BCE
Aristotle
Aristotle declared that all matter was made of only four elements. Those elements being fire, air, water and earth. He also believed that matter had just four properties:hot, cold, dry and wet. He would have constant debates with Democritus about state of matter. This was for one reason. That reason is he didn't believe in the Atomic theory. He stuck by his thoughts of the four elements.This led to the death of the atomic theory for nearly 2 centuries -
375 BCE
Aristotle atomic model
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Dalton
Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms. Dalton was the one to bring atomic theory back from the dead. Dalton theorized that all matter is made of atoms. He saw atoms as the smallest thing in the universe. He was the one who also saw them as uncuttable. He also theorized that they are indestructible. All atoms of a given element are exactly alike and atoms of different elements are different -
Dalton atomic theory
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Thomson
J.J. Thomson was the first scientist to discover that the atom was made up of smaller parts. He discovered that there was a negative energy in the atoom. This negative energy was the electron. While he did not discover it this also led to the findings of protons. He compared it to chocolate chips in a chocolate chip cookie Where the cookie was the atom and the chips were the electrons. He would also compare it to raisins in pudding. His model of the atom was called the "Plum Pudding" model. -
Thomson atomic model
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Einstein
Einstein was the one who mathematically proved the existence of atoms. He also calculated the estimated size of an atom. Along with the weight depending on the element. This helped realize how small the atom truly was and helped see what it could possibly be made of. He also helped with the creation of the periodic table. He did this with his Theory of Relativity. He was also aided by the past work in Atomic Theory. This led to an element being named after him. -
Einstein atomic model
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Rutherford
Ernest Rutherford was the one to discover that the Atom in fact had a nucleus. He did an experiment using positively charged particles fired at gold foil. He said the nucleus was the smallest part in the atom. He also discovered the atom is mostly empty space. He also discovered the electrons circle the nucleus. He also stated the nucleus was fully positively charged. His discoveries led to the exploration of the nucleus. -
Rutherford atomic model
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Bohr
Niels Bohr theorized that the mass of the atom was mostly in the nucleus. He also was the one who theorized electrons in fact orbited the nucleus. He also was the one to determine the energy levels of each orbit. He also discovered how the electrons orbited in different numbers. The first ring had two electrons and all the following rings would have eight. He compared it to the solar system. As in how the planets orbit the sun. -
Bohr atomic model
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Schrodinger
Schrodinger developed a new model for electrons. He did this by making a mathematical equation for the distributions of the electron. This model uses wave functions of the placements of electrons. He couldn't get a physical model however because you could not make one out of wavelengths. The model did not tell us where the electron is but where it might be. However this model showed how it could occupy a 3D space. That way we could see it could orbit around like a sphere instead of a circle. -
Schrodinger atomic model
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Heisenberg
Werner Heisenberg contributed to atomic theory through his work in quantum mechanics. He used matrices in discovering the uncertainty principle. Which states that a particle's position and momentum cannot both be known exactly. He worked with Schrodinger. Although their work contradicted, they went hand in hand in how to locate the particles inside an atom. His work in quantum mechanics also helped him discover the parts of an atom. He helped Schrodinger with his discovery of how electrons orbit -
Heisenberg atomic model
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Chadwick
James Chadwick was most known for his discovery of the neutron. He was the one that the nucleus is not made of just positive charged particles. He discovered that it is in fact made if protons and neutrons. This helped calculate the mass of different atoms. He also discovered that neutrons could split the nucleus. This led to the first nuclear fission. It also led to the creation of the atomic bomb. -
Chadwick atomic model
