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465 BCE
Democritus' Atomic Theory
Democritus invents the earliest known atomic theory, in which he stated that...
1.All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogenous.
5. Atoms differ in size, shape, mass, position, and arrangement. -
Robert Boyle publishes Boyle's Law
Robert Boyle defined the modern idea of an 'element', as well as introducing the litmus test to tell acids from bases, and formed the Royal Society in London. -
Isaac Newton publishes his Atomic Theory
Like Richard Boyle, Sir Isaac Newton studied gases, and the possibility of atoms existing. He theorized a mechanical universe with small, solid masses in motion.A year later he would be knighted in recognition of his scientific discoveries. -
Lavoisier defines elements
Antione-Laurent de Lavoisier defined an element as a substance that cannot be broken down into a simpler substance by a chemical reaction. -
Johann Döbereiner classifies the elements
He arranged some of the elements into groups of three, with the members of each group having related properties. He termed these groups triads, and in 1817, he put forward his Law of Triads. This was a critical step in the creation of a modern periodic table. -
Dmitri Mendeleev creates the Periodic Table
The periodic table created by Dmitri Mendeleev is very similar to the one we use today, with a few changes and additions. -
Albert Einstein proves the existence of atoms
Albert Einstein explained the equivalency of mass and energy, expressed by the famous equation e=mc2. Einstein also mathematically proved the existence of atoms, and thus helped revolutionize all the sciences through the use of statistics and probability. -
Robert Millikan measures the charge of an electron
Using his oil-drop experiment, he discovered that elementary charge is one of the fundamental physical constants, and accurate knowledge of its value is of great importance. -
Niels Bohr introduces the Bohr Atomic Model
The Bohr diagram depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. -
Henry Moseley re-sequences the Periodic Table
One short year before he was killed in action while fighting at Galipolli, Henry Moseley was able to re-sequence the periodic table by nuclear charge, rather than by atomic weight.
