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500 BCE
The Alchemists
The Alchemists developed the theory that all metals are composed of mercury and sulfur and that it's possible to change base metals into gold. -
427 BCE
Plato
He introduced the atomic theory in which ideal geometric forms serve as atoms. -
400 BCE
Democritus
He introduced the idea of the atom as the basic building block of matter. He thought that atoms are tiny, uncuttable, solid particles that are surrounded by empty space and constantly in random motion. -
Robert Boyle
He helped develop a definition of an element (any substance that can be broken into 2 or more substances is NOT an element) and he also helped with "the death of the four elements". -
Antone Lavoiser
He helped explain the law of conservation of mass and determined oxygen an essential substance also helping with "the death of the four elements". -
The Billiard Ball Model
The Billiard Ball Model created by John Dalton suggested that atoms are the smallest particle of an element, that atoms of different elements have different masses, and that they are solid, indestructible units, kind of like billiards ball. -
John Dalton
He was the 1st scientist to explain the behavior of atoms in terms of the measurement of weight. -
Amedeo Avogadro
He had to resolve the confusion at that time about atoms and molecules. He clearly distinguished one from the other, stating that gases are composed of molecules and these molecules are composed of atoms. -
Dmitri Mendeleev
Dmitri invented the periodic table of elements, explaining all the elements. -
JJ Thompson
JJ Thompson discovered electrons and also helped understand the atom's basic structure. -
Pierre and Marie Currie
They discovered the strongly radioactive elements polonium and radium, which occur naturally in uranium minerals. They also coined the term radioactivity. -
The Plum Pudding Model
JJ Thompson created this model trying to explain 2 properties of atoms then known: that electrons are negatively charged particles and that atoms have no net electric charge. -
Albert Einstein
Albert Einstein mathematically proved the existence of atoms and proved that matter can be manipulated. -
Robert Milikan
He deduced the electric charge of an electron. This discovery was made from his famous oil-drop experiment. -
Ernest Rutherford
He discovered the alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. He also postulated the nuclear structure of the atom. -
Neils Bohr
Neils proposed the theory for the hydrogen atom, based on the quantum theory that some physical quantities only take discrete values. -
The Solar System Model
Created by Neils Bohr, the Solar System Model describes an atom as a central positive entity (nucleus/sun) and orbiting around it, the negative entities (electrons/planets). The problem with this is that electrons are positively charged. -
Henry G.J. Mosely
He created the concept of the atomic number and helped understand its meaning. -
Erwin Schrodinger
He combined the equations for the behavior of waves with the Brogle equation to generate a mathematical model for the distribution of electrons in an atom. (The Electron Cloud Model) -
The Electron Cloud Model
Created by Erwin Schrodinger, the Electron Cloud Model was a model of the atom where the atom consisted of a small but massive nucleus surrounded by a cloud of rapidly moving electrons. The model says we can't know exactly where electrons are at any given time, but they're more likely to be in certain areas. -
Werner Heisenberg
He created the uncertainty principle stating that electrons don't move in a neat fashion around the nucleus of the atom. He also created the neutron-proton model of the nucleus. -
James Chadwick
He discovered the neutron which directly led to the development of the atomic bomb. He later regretted this discovery.
