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500 BCE
The Alchemists
The Alchemists were a group of intelligent scholars and theorists who conducted experiments. The Alchemists created four elements, fire, earth, air, and water, which they believed could combine them to create more valuable metals like silver and gold. They also laid the foundation for the modern day periodic table of the elements. -
440 BCE
Plato
Plato was a philosopher born in Athens, Greece. He believed that the "real world" wan not really the world that we were living in. He thought that the solar system was the center of the one and only universe to ever exist. Similar to the atom's structure, he believed that stars and planets were spun around the sun on orbitals. Plato also believed that there were four elements, water, air, fire, and earth similar to The Alchemists. -
400 BCE
Democritus
Democritus was a philosopher born in Greece. He believed that atoms were infinite, that there was no specific number for how many atoms were in or universe. He believed that atoms kept moving steadily until stopped and that they were basically indestructible. He thought that atoms were solid, incompressible, and all the same. -
Robert Boyle
Robert Boyle was a philosopher from Ireland. Boyle believed that all substances were made up of atoms, or in his own terms, corpuscles. He did not believe that all atoms were uniform, he thought that they could be different sizes and different types. -
Antoine Lavoisier
Antoine Lavoisier was a chemist from France. Through many experiments, Lavoisier found out that the reactants and mass in a chemical reaction always stays the same no matter what variables are added. He also discovered that oxygen played a major role in whether a substance was combustible or not. He even got to name the element. -
Billiard Ball Model
The Billiard Ball Model was an atomic model developed by John Dalton. Dalton believed that atoms were perfectly circular and incompressible, so he began using billiard balls in many of his experiments to show atoms because atoms are far too small for the human eye to see. -
John Dalton
John Dalton was a chemist born in England. Dalton was the first scientist that tried to fully describe matter and he is credited for creating the first modern atomic theory. This modern theory was based on the fact that everything in our universe is composed of atoms and that atoms are invisible. He did have to eventually modify some parts of his atomic theory as discoveries of isotopes and subatomic particles were made. -
Amedeo Avogadro
Amedeo Avogadro was a scientist from Italy. Avogadro was most famous for his hypothesis that if two volumes of gas were the same, then they would both contain the same number of molecules. He also discovered that other gases like hydrogen, nitrogen, and oxygen were made up of more than one kind of atom. -
Dmitri Mendeleev
Dmitri Mendeleev was a chemist from Russia. Mendeleev founded the basics of the periodic table of the elements. This periodic table ranked elements from lowest to highest atomic number. Although Mendeleev did not know of nearly as many elements as we do today, his work still laid the foundation for the modern day periodic table of the elements. -
JJ Thomson
JJ Thomson was a physicist from Britain. Thomson discovered the electron. He figured out that within every atom, there were electrons on orbitals spinning around the nucleus. He also discovered that the electron was negatively charged. The electron was the first subatomic particle to be discovered inside of an atom. -
Pierre and Marie Curie
Marie Curie was a physicist and chemist from Poland and Pierre Curie was a physicist from France. Together, they researched radioactive elements and materials. Eventually, they discovered the elements radium and polonium. They also won the Nobel Prize for Physics, and later also won the Nobel Prize for Chemistry. -
Niels Bohr
Niels Bohr was a physicist born in Denmark. Bohr helped us understand an atoms structure. He was also the first person to propose the hydrogen atom. He also figured out that electrons travel on orbitals around an atoms nucleus and that the number of electrons on all orbitals of an atom determines its atomic number. -
Plum Pudding Model
The Plum Pudding Model was an atomic model developed by JJ Thomson after his discovery of the electron. This model depicted that, like a plum in pudding, inside of a nucleus of an atom with a positive charge, were many negatively charged electrons. -
Albert Einstein
Albert Einstein was a physicist born in Germany. Einstein helped prove that atoms exist with the help of his own theory of relativity and many mathematic equations. He also proved that all liquids are made up of molecules, and that liquids are always in movement in a random motion even when still. -
Ernest Rutherford
Ernest Rutherford was a physicist from New Zealand. Rutherford discovered that the atom was mostly empty space. He realized that in the center of all atoms there was a central nucleus containing protons and neutrons, and that on the outer orbitals there were electrons. He discovered that in between the orbitals (if there were >1) and within the space going from the orbitals to the nucleus, there was just empty space. He also figured out that most of an atoms mass was held inside of the nucleus. -
Robert Millikan
Robert Millikan was a physicist from the United States. Millikan proved that there was always an electrical charge in an atom. An electrically charged atom is called a proton. He used an oil drop experiment to determine this principle. This experiment was performed at the University of Chicago. It's goal was to measure the electric charge in an atom. It also helped prove that subatomic particles existed. -
Solar System Model
The Solar System Model was an atomic model developed by Niels Bohr. It showed that the sun was the center of our solar system with planets and stars rotating in perfect circles around the sun. This model is similar to the atom because the atom has a nucleus with many electrons rotating around it at a very high rate of speed. -
Henry Moseley
Henry Moseley was a physicist from England. Moseley discovered that the number of protons in an atoms nucleus is equal to the atoms atomic number. This laid down the foundation for the modern day periodic table of the elements. This discovery allowed him to be able to predict more elements to come, of which he predicted four, and of those four, all were eventually found. -
Erwin Schrödinger
Erwin Schrödinger was a physicist from Austria. Since, by this point in time, scientists already knew that the electron was a fundamental part of any atom, Schrödinger is credited for discovering the mathematical equation for discovering where an electron would be and when. He is also credited for his work with quantum mechanics and the quantum theory. -
Electron Cloud Model
The Electron Cloud Model was an atomic model developed by Erwin Schrödinger. The model is centered around an atom, which has many electrons traveling around a nucleus at a very high rate, making them hard to distinguish, therefore looking like clouds. These electrons were not depicted on orbitals, but solely spinning around the nucleus of an atom. -
Werner Heisenberg
Werner Heisenberg was a physicist from Germany. Heisenberg determined that the location and momentum of a subatomic particle are always unknown. This came to be known as the "uncertainty relation". Heisenberg also worked on the German atomic program in the 1940's. -
James Chadwick
James Chadwick was a physicist from Britain. Chadwick discovered that neutrons were also part of the atom, like the already discovered proton. He discovered that the neutron was a particle that contained no electric charge whatsoever, therefore being neutral.
