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500 BCE
The Alchemists
The alchemists were the first people to start to decipher the composition of objects. Source: prezi.com/t50cihtay12m/alchemyanditscontributionstotheatomictheory -
430 BCE
Democritus
Democritus believed all matter was composed of small particles; atoms. He believed they were indivisible.
Source: breakingatom.com/evolutionoftheatom -
427 BCE
Plato
He discovered atoms of matter must derive from fundamental shapes. Source:uoregon.edu/glossary/plato -
Robert Boyle
Robert Boyle proposed elements can't be broken down into simpler substances. Source: sciencehistory.org/historicalprofile/robertboyle -
Antoine Lavoiser
He theorized that the total mass of products and reactants in a chemical reaction are the same, so therefore created the Law of Conservation of Matter. Source: famousscienntists.org/antoinelavoiser -
John Dalton
Dalton proposed all matter was composed of atoms, indivisible and indestructible building blocks. This led him to believe that they were built like a billiard ball, which led him to make the Billiard Ball Model. Source:courses.lumenlearning.com/introchem/chapter/johndaltonandatomictheory -
Amedeo Avogadro
He found that equal volumes of gases at the same temperature and pressure have equal molecules. Source: sciencehistory.org/avogadro -
Dimitri Mendeleev
He was the first person to order elements in the periodic table.
Source: breakingatom.com/learntheperiodictable -
JJ Thompson
He created the Plum Pudding Model of the atoms, using cathode tubes, and found the electron. Source: breakingatom.com/historyoftheatomicmodelthompson -
Pierre and Marie Curie
They discovered two new elements, and found rays of uranium came from the atomic structure. Source: atomicheritage.org/mariecurie -
Albert Einstein
He mathematically proved the existence of atoms.
Source: ans.org/alberteinstein -
Ernest Rutherford
He found the atom had a mass of positive charge at the center.
Source:britannica.com/biography/rutherford -
Robert Millikan
He found the magnitude of the electron's charge.
Source:sutori.com/developementofatomictheory -
Neils Bohr
Neils Bohr proposed that electrons move around the nucleus, but only in prescribed orbits. He also proposed the Solar System Model of the atom, which said that those same electrons orbit the nucleus of an atom like the sun in a solar system. Source: www.nobelprizes,org/prizes/physics/bohr/facts -
Henry Mosely
He found the atomic number, which is the number of positive charges in the atomic nucleus. Source: britannica.com/biography/henryMosely -
Erwin Schrodinger
He created the electron cloud model, which said that we can't know where an electron is at any given time, but the electrons are likely to be in specific areas. The reason it is called the electron cloud model is because he said electrons were like waves, treating them like as clouds of negative charge. Source: breakingatom.com/thehistoryoftheatomicmodelschrodinger -
Werner Heisenberg
He developed a mathematical way of expressing the energy levels of the electrons in atoms. Source: breakingatom.com/thehistoryoftheatomicmodelheisenberg -
James Chadwick
He discovered neutrons at the center of the atom.
Source: breakingatom.com/historyofatomicmodelchadwick