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Period: 475 BCE to
Atomic Theory Timeline
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Period: 475 BCE to
Atomic Researchers
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460 BCE
Democritus
One of first ever chemists, theorized that the atom made up everything and that different elements were made up of different atoms. -
350 BCE
Alchemists
Scientists, who speculated and attempted to convert simple metals into something more valuable such as gold or silver. Attempted to use Aristotle’s ideas and change the atomic composition of matter/elements, and change it’s compound structure in a way where it was a whole new substance all together. -
460
Democritus
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John Dalton
One of the first chemists, known for introducing the atomic theory, which was how all matter was compromised of indivisible and indestructible atoms, and his research in color blindness. -
Law of Definite Proportions
Defines that a given chemical compound always contains its component elements in fixed ratio and doesn’t depend on its source. -
Antoine Lavoisier
Found the role that oxygen played in combustion and deposed the phlogiston theory. He also helped make the metric system and name some of the first elements. -
Law of Conservation of Mass
An atomic law which states that matter cannot be created nor destroyed under any circumstances, only transferred. -
Joseph Louis Proust
French chemist who is best known for his laws of definite proportions, and proved that relative quantities of any given compound’s constituent elements remain invariant. -
Dalton's Atomic Theory
Dalton’s four theories that were based off of the law of conservation of mass and the law of conservation. The four theories were that all matter is made of atoms which are invisible, all atoms of a given element are identical in mass and properties, compounds are combinations of two or more different types of atoms, and that a chemical reaction is a rearrangement of atoms. -
Cathode Ray Tubes
Streams of electrons are observed in discharge tubes, the glass tubes are strapped with electrodes and the electricity is applied, the glass behind the positive electrode will glow, revealing a positive charge. This proved the existence of subatomic particles. -
Dmitri Mendeleev
He formulated periodic law and a version of the periodic table of elements. His table was the first that classified elements by their atomic number -
JJ Thompson
Theorized that atoms were made up of tiny particles, and that there was a positively charged cloud within the atom, filled with electrons.
Using cathode rays, discovered that there were electrons within the atom, and the atom was in fact not the smallest particle known to man.
Created the plum pudding model in 1904 -
Plum Pudding Model
Model made by J.J Thomson, where the neutrons in his atomic model, look like plum seeds, surrounded by the pudding, which is the positively charged cloud, both of these within the atom itself. -
Gold Foil Experiment
Important series of experiments which gave scientists at the time insight to the nucleus within an atom
Came to conclusion that each atom has a nucleus where it’s mass and positive charge was held
They came to this conclusion by observing how an alpha particle beam was scattered when it struck a thin sheet of metal, which in fact was gold. -
Robert Millikan
Discovered the magnitude of the electron's charge. He found this using the oil drop experiment where he surveyed how drops of oil moved. -
Oil Drop Experiment
This was the experiment that Robert Millikan used to find the magnitude of the electron's charge. The experiment involved a slightly charged drop of oil that was dropped between two metal plates and he would observe how the drops of oil moved. -
Nuclear Model
Rutherford’s atomic model has the protons and neutrons in the center with electrons orbiting around the protons and neutrons in an electron orbit. -
Niehls Bohr
Physicist who made foundational contributions to understanding atomic structure and quantum theory. Proposed the Planetary Model, which portrayed small neurons floating around the nucleus of an atom. -
Planetary Model
Proposed by Niels Bohr, it is a model of the atom in which negatively charged electrons orbit a small positively charged nucleus, and it is called this as it is similar to planets orbiting the celestial body of the sun. -
Henry Moseley
English physicist whose science contributions included discovering a systematic relation between wavelength and atomic number. He made many groundbreaking contributions to spatial synthetic neuron transmitting. -
Quantum Mechanical Model
A proposal by Erwin Schrodinger that made a new model called the quantum mechanical model of an atom which treats electrons as matter waves. Is based around the theory that matter has wave like properties. -
Erwin Schrodinger
Him and Heisenberg solved math equations that were used to prove Bohr’s theory of the atom by finding where the electrons were located . This led to them making the atomic model where the protons and neutrons are in the middle while the electrons are on the outside. Mapped out what the modern atom looks like. -
Werner Heisenberg
Partnered with Erwin Schrodinger for many years, worked on quantum physics and made contributions to notions which were used to create the most accurate atom representation at the time. -
James Chadwick
First chemist to discover neutrons truly with nuclear sciences and researched a lot on nuclear fission and the properties that contained.
