DEMOCRITUS (CIRCA 470 B.C)
Democritus said that all matter is made up of tiny,
indivisible particles called atoms. These atoms were completely
solid and were eternally in motion.
ARISTOTLE (384 BC)
Aristotle said that atoms were composed of the four
elements: fire, water, earth, and air. Each of these atoms had
certain properties depending on what they were made of:
hotness, dryness, wetness, or coldness. This contradicted the
work of Democritus and put a second theory in use for almost
2000 years (before it was disproved). Aristotle admired
Democritus as a role model.
JOSEPH-LOUIS PROUST (1793)
Proust proved that the relative quantities of any given pure
chemical compounds’s constituent elements remain invariant,
regardless of the compound’s source. This is known as Proust’s
law, or the law of definite proportions.
ANTOINE LAVOISIER (LATE 1800’S)
Antoine Lavoisier formulated the theory of conservation of
mass. This showed that matter couldn’t be created or destroyed,
which supported the theory of Democritus. Lavoisier also showed
that compounds are simply combinations of different types of
atoms, further supporting the idea that atoms are indivisible.
Lavoisier provided crucial information for John Dalton’s model.
JOHN DALTON (1803)
Dalton compounded all the work of Lavoisier and
Democritus into one, single atomic theory. This theory stated that
all matter is made of indivisible and indestructible atoms, all
atoms of a given element are identical, compounds are
combinations of elements (atoms), and a chemical reaction is
merely a rearrangement of atoms.
MICHAEL FARADAY (1832)
Faraday Studied the effect of electricity on solutions,
"electrolysis" as a splitting of molecules with electricity,
developed laws of electrolysis.
HENRI BECQUEREL (1896)
Becquerel discovered radioactivity in his research of
uranium and other materials. This helped to show what
happened when atoms were affected and observed. Becquerel
shared a Nobel Prize with the Curies.
J.J. THOMSON (1898)
Thomson conducted an experiment with a cathode ray tube,
and bent the path of the rays with magnets. He interpreted this
as evidence of much smaller particles, which he called electrons.
Using this, he formulated the plum pudding model, which added
negatively charged electrons into the positively charged solid part
of the atom. Thomson was the teacher of Ernest Rutherford.
MARIE AND PIERRE CURIE (1898)
The Curies enhanced the understanding of radioactivity
through their research of radioactive materials (discovering
radium and polonium). This helped to show what happened when
atoms were affected and observed. The Curies shared a Nobel
Prize with Henri Becquerel.
MAX PLANK (1900)
Max Planck created the quantum theory, which was later
used by Niels Bohr to create his model of the atom.
ALBERT EINSTEIN (1905)
Einstein best known for his Theory of Relativity and his
mass energy equivalence formula E = mc2. He is also famous for
creating the first Atom Bomb.
ROBERT MILLIKAN (1908)
Robert Millikan discovered the exact charge of the electron
in his “Oil Drop Experiment”, enhancing the model of J.J.
Thomson. He created this experiment with the aid of Harvey
Fletcher.
ERNEST RUTHERFORD (1909)
In Rutherford’s experiment he
shot alpha particles at gold
foil, expecting them to pass right through. Some bounced back,
however, and he formulated the planetary model, which showed
that most of the mass of an atom was concentrated in the center
(the nucleus). Ernest Rutherford was the student of J.J. Thomson
(he was trying to prove Thomson’s model with his experiment, but
ended up disproving it).
NIELS BOHR (1913)
Niels Bohr said that electrons had quantified amounts of
energy using Planck’s Quantum theory. He proposed a new
model of the atom where the electrons travel around the nucleus
in orbits determined by their energy levels.
JAMES CHADWICK (1931)
James Chadwick discovered the neutrally charged neutron,
the discovery that ultimately led to the atomic bomb. He
enhanced Bohr’s model by adding neutrons to the nucleus.
http://www.timetoast.com/timelines/the-history-of-the-atom--4