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465 BC:
A Greek philosopher, Democritus,
also known as the father, of atomic
thought came up of a theory in
465BC. He hypothesized that
the universe is composed of two
elements: the atoms and the
void in which they exist and move.
He deduced that all matter is made of
an infinite amount of invisible atoms
that vary in size, density, shape, and temperature.1803 AD:
John Dalton, a chemist and
schoolteacher performed
various experiments related
to atoms such as mixing
gases and explaining compounds.
In 1803, he came up with
the very first atomic theory:
Atoms of the same element
are identical, Atoms of different
elements have different weights
and chemical properties,
compounds are formed when
elements are combined and
atoms cannot be created or
destroyed. He also created the
very first model of what an atom
would look like.1896 AD:
Frederick Soddy, a radio-chemist
who worked in nuclear chemistry
studied the 1896 radioactivity
phenomenon and he discovered
after a chain of experiments that
atoms could have the same chemical
properties but can change those
properties when it came to radioactivity.
In 1913 Soddy claimed a new theory
that atoms can have isotopes that
change its weight.1900 AD:
Max Planck, a German physicist,
famous for his work in thermodynamics,
he announced that hot glowing
matter radiates energy in
small amounts or packets,
not one continuous wave.
This is known as Planck’s constant
from 1900.1897 AD:
In 1897, J.J Thompson demonstrated
that atoms were made up of even
smaller particles called electrons,
which gave the atom a (-) charge
through electric field experiments.
His model of an atom was known as
a raisin bun model and was an
improvement of Dalton’s model,
with added electrons.1911 AD:
Following closely in 1911, a
scientist, Earnest Rutherford
designed an experiment that
founded the protons and the
nucleus. The protons had a (+)
charge and was placed in the
middle of the atom, called the
nucleus and the electrons
encircled the nucleus, the rest
mostly being empty space.
His model was named the Plum
Pudding model.1913 AD:
Niels Bohr, a Danish physicist
improved on Rutherford’s model,
claiming that electrons moved in
specific layers or shells and each
shell could only have a certain
number of electrons. His model
was announced in 1913 and is
known as the Bohr model.1932 AD:
James Chadwick, working with
nuclear physics used alpha
particles and discovered the
neutron, the same mass as a
proton and is found in the nucleus.
They also had no charge and this
model was a major improvement
from Bohr’s model.
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