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100
Democritus
Democritus lived from 460 BC to 370 BC. Democritus discovered that invisible particles or atoms make up all of the matter that exists. Democritus was the person to call the atom the atom. He got the name from the Greek word, “atomos” which means uncuttable. Democritus was also the first person to create a model of the atom. Even though it was just a solid sphere, it was something. What Democritus did not realises is the fact that neutrons, electrons, protons and a nucleus was present in an atom. -
Period: 100 to
history of an atom
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150
Aristotle
Aristotle lived at around 350 B.C. he was a Greek Philosopher. He disagreed with the model Democritus created. Most of his ideas were not created based on science, more on thought. This is why Aristotle strongly disagreed with Democritus. He believed that substances were made of earth, fire, water or air and that there was not a smallest part of matter. Because Aristotle didn’t believe that atoms existed, he never made an atomic model -
Antoine Lavoisier
The French nobleman, Antoine Lavoisier, founded several elements, e.g. oxygen, hydrogen and nitrogen, and placed them on the first periodic table of elements together. Lavoisier used the ideas of Aristotle of the fire, earth, water and air to create experiments investigating oxidation and combustion. He discovered important elements such as hydrogen, oxygen and sulphur by using previous knowledge of atomic bonding. Lavoisier discovered that water is made up of hydrogen and oxygen and that air in -
John Dalton
The English chemist John Dalton is the person that created the atomic theory of matter, composed of both his findings and previously found by Democritus. His theory was that matter is made up of atoms and that these atoms cannot be created nor destroyed. It also included that atoms of different elements form chemical compounds by combining. This theory later would contribute in advancing the atomic model -
Henri Becquerel
Henri Becquerel was born with a family of scientists. His father and grandfather had influences on Becquerel and worked with properties of atoms, things such as magnetism and radioactivity. Becquerel’s biggest achievements were in the radioactivity field. Becquerel’s earlier work included the light absorption of crystals. Becquerel also looked at the mechanics of X-rays. The perfection of the atomic model was partly to do with Becquerel’s discovery of radioactivity -
Niels Bohr
The Danish scientist, Niels Bohr, was a student of Rutherford. Bohr decided to recreate the atomic model based on the previous one made by Rutherford. One of the only changes he made was the orbit of the electrons. Bohr also created energy levels in the atom. This means that only a certain amount of electrons could fit on one energy level of the atom -
J.J. Thomson
When it came to the atomic model, J.J. Thomson was a very important man. All of the models of an atom before Thomson were just big solid spheres. Thomson’s discovery of the electron led him to create the Plum Pudding model of an atom. In this model, he came to believe that there were mostly positive and negative electrons wondering around the atom. The making of this model was an influence on other scientists to create more in depth models -
Max Planck
The Quantum Theory was created by the German scientist, Max Planck. Planck’s theory started that energy was given off in little packets if energy. When talking about light, these were called photons. He discovered that energy is restricted to specific quantities when in wave form. The understanding of energy in atoms was because of this discovery -
Marie and Pierre Curie
The European couple, Marie and Pierre Curie’s contribution to atomic chemistry was exploring the mysteries of radioactivity. Marie decided to look further into Becquerel’s discovery of radioactivity. The husband and wife team won the Nobel Peace Prize for their works in radioactivity after discovering the elements radium and polonium. Marie’s discovery later added to the atomic model. -
Robert Millikan
The American scientist Robert Millikan was particularly interested in the findings of the electron by J.J. Thomson. Thomson had a prediction that the atom was 1000 times larger than an electron. Millikan wanted to prove Thomson’s hypothesis. An ‘oil-drop experiment’ was performed by Millikan and proved Thomson correct. Millikan was an inspiration to other scientists and inspired them to explore parts of the atom -
Ernest Rutherford
Ernest Rutherford, another scientist to change the atomic model, felt that J.J. Thomson’s model was incorrect. So he created another one. He said instead of positive matter being in the whole atom, it was just in the middle, the nucleus. Rutherford said that the positive nucleus was surrounded by electrons and that it was mostly empty space. One of his own students was influenced by this model that later, he perfected the atomic model -
Erwin Scrhodinger
The Australian Scientist Erwin Scrhodinger worked with the quantum model of the atom. Scrhodinger disagreed with Bohr’s theory so he create his own. Scrhodinger believed that the only way to find the energy and the location of an electron in an atom was to calculate the probability of it being a certain distance from the nucleus. The quantum mechanical model of the atom was influenced by this equation -
Henry Moseley
In order to create the real atomic number, the English scientist Henry Moseley worked with Niels Bohr. X-rays were used by Moseley to find the frequencies of elements in the periodic table. Atomic numbers were just numbers given to random elements before Moseley’s discovery. These frequencies were used by Moseley to fins the amount of protons in the nucleus correlated with the atomic number. This created Moseley’s law -
James Chadwick
The English scientist, James Chadwick, was the one to discover the neutron. Rutherford had concluded that the nucleus was made of positive matter before this discovery. Because of the negative electron and the positive protons, it made sense that the atom was neutral as they cancel out each other. Chadwick stated questioning why there was a difference between the number of protons and the atomic mass. This led Chadwick to find the missing component was a neutral part: the neutron -
Werner Heisenberg
The proposal of the uncertainties of the quantum model was made by the German Scientist Werner Heisenberg. Heisenberg proposed that nobody can know the exact velocity and momentum of the electron at the same time. This means that you can’t know the exact location of the electron. Because of the uncertainty of the location of the electron, this principle proves there was an error in Bohr’s Model
