Atomic Theory Timeline Assignment

Democritus was the premiere Ancient Greek Philosopher who presented the theory that all mater was made up of atoms. He believed that there existed individual particles which were indivisible, and that they merged together and interacted with each other to create everything in the world. His beliefs formed the basis of our current Atomic Theory, even though it only emerged over a thousand years after his death.

Alchemists believed that they could transmute certain base metals into gold, and they also believed that all matter was made up the four base elements: earth, wind, fire, and air, and that certain combinations of each would produce certain matter. They ended up paving the way for modern science to follow, by discovering the basics of chemistry and elements, which allowed for further knowledge to be developed, an eventually grow out of the assumptions of alchemy.

John Dalton conceptualized the first modern atomic theory, specifically suggesting that all atoms of a given substance are identical, and that atoms can combine together to form compounds at fixed ratios. He stated that atoms cannot be destroyed through chemical means, only transformed. His atomic theory allowed for future advancements in chemistry, and set the groundwork for future development of the atomic theory.

J.J. Thomson sought to find out how atoms were constructed, and how they gained physical properties, and focused specifically on the charge of atoms. He used a cathode ray tube to discover that part of the atom is negatively charged, and later found that it took up very little space, and weighed almost nothing. He named the sub-atomic particle the electron, and proposed that atoms are spheres, with electrons evenly dispersed throughout. This model is called the plum pudding model of the atom.

Marie Sklodowska Curie was a Polish scientist who is the only woman to have won two Nobel prizes. Her most significant contribution to atomic theory was her part in discovering and coining the term radioactivity, and the decay of molecules, as this was a large step in our knowledge of the behaviors of atoms, and the idea of radioactivity is now instrumental in today's world.

Hantaro Nagaoka was a Japanese scientist who theorized that the atom was a positively charged sphere, with hundreds of electrons orbiting it, similar to how Saturn's rings orbit the planet. Thus, this model of the atom was called the Saturnian model, and was one of the first models of the atom that included a nucleus in the center, rather than the entire atom being a single sphere. His ideas served as a turning point in atomic theory, and his idea of the nucleus was confirmed eight years later.

Ernest Rutherford conducted an experiment using gold foil and alpha particles, which are structurally identical to helium nuclei, and tested whether the alpha particles would pass through the gold foil, or be deflected by it. He discovered that only some alpha particles were deflected, which lead to the realization that there was a dense, positive core in an atom, which was named a nucleus, and was made of protons, and he also theorized the existence of another subatomic particle with no charge.

Niels Bohr discovered that when energy is added to an atom, they emitted certain patterns of light, specific to the type of atom they were. Bohr theorized that the light was being released due to the emission of the absorbed energy of the electrons, and that there were set energy levels that the electrons orbited, and that as you add energy, the electrons jump levels, and then release the energy as they return. This spawned a new model of the atom, the planetary model.

Max Planck contributed to our knowledge of Atomic Theory by discovering quantum mechanics, which described how particles interact at the most fundamental level. These discoveries allow us to understand atoms and particles at a brand new scale, and to conduct new research into more specific sections of atomic theory, such as subatomic particles, or wave theory.

Albert Einstein's work has contributed to almost every realm of physics, and his discovery of the photoelectric effect was a crucial step in the beginning stages of quantum theory. Einstein's letter to Roosevelt regarding nuclear fission bombs kick-started the Manhattan Project, where we discovered the immense power of the atom, and the energy associated with the bonds that is released when the bonds are broken. While this knowledge was first used for bombs, it is now used as sustainable energy.

Louis de Broglie discovered and suggested that all matter behaves in certain ways like waves, in a theory that was an example of wave-particle duality, and this discovery was one of the most revolutionary discoveries in quantum theory. The wave-particle duality introduced a whole new realm of understanding of atomic theory, and allowed for numerous subsequent experiments.

Satyendra Bose was an Indian scientist who developed the prediction of the Bose-Einstein Condensate, which led to the discovery of the boson, one of the two classes of subatomic particles. The credit for this discovery is given to Peter Higgs, but the theory was crafted by Bose. This discovery began a whole new section of atomic theory, where suddenly atoms were not the smallest thing in the universe, as they were made up of smaller particles, like bosons.

Wolfgang Pauli built upon the idea of assigning quantum numbers to electrons, and introduced two new quantum numbers, and stating that no two electrons can have the same set of quantum numbers. This helped ease concerns regarding inconsistencies with observations, and how the observations related to the new quantum theory. Later, when protons and neutrons started being assigned quantum numbers, Pauli's principle regarding unique sets of quantum numbers also applied to nuclear particles.

Erwin Schrodinger helped deepen our understanding of quantum theory and quantum mechanics, as he was able to determine an equation which could be used to model the wave function of a system, which was a key factor in continuing the study of quantum mechanics, furthering the knowledge we have on the behaviors of atoms and our world.

Werner Heisenberg is most well known for the Heisenberg Uncertainty Principle, which states that you cannot precisely know both the energy associated with an electron, as well as its location. Heisenberg's discovery also described how electrons do not follow set orbits around the nucleus, and instead exist in 'clouds' around the nucleus once more redefined our model of the atom, and provided us with significantly more understanding of the atom.

James Chadwick built on Rutherford's discoveries, and proved the theory of the neutral particle, the neutron. With the discovery of the neutron, more accurate prediction and models could be made, as we now knew all three subatomic particles that are used to form atoms - the electron, proton, and neutron. This set of discoveries was a large step in our understanding of atomic theory, and allowed us to theorize deeper about how atoms interact with one another.

Gerard was a German chemist who fled Germany during the rise of the Nazi party, and conducted most of his research in Canada. He worked to discover the electronic structure and geometry of molecules, and so helped set the base for molecular spectroscopy. He later discovered the light spectra of certain "free radicals" during certain reactions, and used them to discover and identify the spectra of interstellar gas, contributing to our knowledge of the stars and outer planets, and atomic theory.

Lise Meitner was an Austrian-born scientist who worked alongside Otto Hahn and Fritz Strassmann to discover uranium fission. She investigated the effects of neutron bombardment, and discovered the energy associated with fission. She was asked to help work on the Manhattan Project, but she declined, as she was not happy with the idea of a fission bomb. Her research showed the power of fission to the world, and allowed us to know the inner mechanisms of radioactivity and beta decay.

Ronald Gillespie was a Canadian chemist who immigrated from London, and did research on the shapes of molecules, and developed VSPER theory, which is used to describe and predict the three-dimensional shape of a molecule in space, based on the electron pairs in the outer shells. This allowed us to properly visualize full compounds in three dimensions for the first time, and is one of the most important developments in molecular geometry, and expanded our knowledge of the properties of atoms.