-
500 BCE
The Alchemists
The Alchemists contributed to the atomic theory because they broke down the chemical compositions of the 4 basic elements during their time, which were water, wind, fire, and earth, which later evolved. Basically, they layed down the foundation of the modern periodic table of elements. -
440 BCE
Plato
Proposed that matter was continuous, infinite, present in every form, and always around us. Also believed that matter could be divided and subdivided into smaller pieces without limit. This was called the continuous theory of matter. -
400 BCE
Democritus
Introduced the idea of the atom as the basic building block of matter. Also introduced the ideas that atoms were uniform, solid, hard, incompressible and that they moved in numbers through empty space till stopped. -
Robert Boyle
He proposed that all elements are made of "copuscles" of different types and sizes, that were able to organize themselves into different groups of chemical substances. Also believed that all substances were composed of atoms -
Antone Lavoiser
Discovered a breakthrough in the atomic model. Found out that the total mass of atoms/products before a chemical reaction is equal to the mass after, and that atoms cannot be created or destroyed in a chemical reaction. This led to the creation of the law of conservation of mass. -
Billiard Ball Model
Dalton believed that atoms were the smallest pieces/particles of matter. He saw them as sold, spheres, which resembles a billiard(pool) ball, so he used them to model the atoms. -
John Dalton
John Dalton proposed/proved/ made the atomic theory, that atoms were a tiny, hard sphere,(made the billiard ball model). He also proposed that compounds were atom from different elements combined together and were made up of atoms that were identical and had also the same mass. -
Amedeo Avogadro
Found 2 hypothesis. One was that equal volumes of gas contains equal numbers of molecules, and that gases such as hydrogen, and oxygen, were composed of 2 atoms. -
Dmitri Mendeleev
Found that if all known chemical elements were arranged in order of increasing atomic weight, it showed a pattern. He invented the first periodic table of elements. -
JJ Thompson
Announced his discovery that atoms were made of smaller compounds. This changed the way scientists thought about the atom, and had major ramifications for the physics field -
Pierre and Marie Curie
They discovered the first radioactive elements of polonium and radium, which occur in uranium naturally. -
Plum Pudding Model
Proposed by JJ Thompson, the model has electrons surrounded by a volume of positive charge, like negatively charged "plums", which is embedded in a positively charged "pudding" -
Albert Einstein
By calculating the force of a grain of pollen floating in the water, he was able to prove the existence of atoms. Also, with this experiment, he was able to determine of the atoms properties. -
Robert Millikan
Discovered that there is a fundamental electric charge in electrons. Also found out that the charge of an electron precisely determines the magnitude of the charge of the electron. -
Ernest Rutherford
Found that the atom is mostly empty space, with Almost all of its mass being concentrated in a "nucleus". Also found that this "nucleus" is mainly postively charged, and surrounded and at a great distance by negativity charged electrons. -
Neils Bohr
Neils Bohr created the Bohr model.(which also was classifed as the solar system model). This was that/ Bohr proposed electrons traveled in defined circular orbits around the nucleus, and that the electrons moved in a fixed orbit with a fixed amount -
Solar System Model
Bohr Developed a new model for the atom. He said that the electrons are put into circular orbits around the nucleus. Bohr's model patterned the solar system, so it is referred to as the solar system model -
Henry G.J Mosely
Concluded that the atomic number is the number of positive charges in the atomic nucleus. He also found 3 new elements, with atomic numbers 43, 61, and 75, which were between gold and aluminum. -
Drwin Schrodinger
Used the Bohr Model, and math equations, to describe the percentile of finding an electron in a certain position. Known as the creator of the quantum, mechanical model of the atom -
Electron Cloud Model
Created by Erwin Schrodinger, is a model of an atom, where the atoms consist of a small but rationally massive nucleus, which is surrounded by a cloud of rapidly moving electrons. -
Werner Heisenburg
Formulated quantum mechanics, and discovered the uncertainty principle, which was that a particles position and momentum cannot both be known exactly. -
James Chadwich
Discovered that atoms consisted of not only protons and electrons, but now neutrons. He discovered the neutron, and he found that it was a neutral subatomic particle, that was almost the same weight as the proton.