Events
Greek Thinkers
400 BCAnaxagoras, Leucippus,
and Democritus developed
the concept of the smallest
possible particle referred to as
the atom. They thought of 4
main elements; Earth, water,
fire and air.He developed the first extensive
element list of 55 substances that
cannot longer be divided into a
simpler substance. His experiments
with oxidation disproved the four
main elements.Antonie Lavoisier
1787Dobereiner
1820Discovered how the relative
atomic mass of the middle
element in a group of three
is almost halfway between
the lightest and heaviest ones
in the group. He called this
pattern “triad”. He organized
many of the elements that
(at the time) were discovered
that way. The difference of
relative atomic mass between
three elements.Dechancourtis
1860De Chancourtois was a French
scientist and the first to arrange
the periodic table considering
the atomic weight of elements.
This way, he made use of a
physical property that can be
represented as numbers.
The elements were arranged
in order of increasing weight.
He arranged the elements in
a cylinder as a spiral called
telluric helix. The helix
allowed to see similar
elements lined up verticallyCannizaro
1860Cannizaro discovered more
accurately the atomic weights
of the elements. He discovered
that by arranging several alkaline
metals in certain order, you
could deduce the atomic weight.He proposed his “law of octave”
in 1864 which organized the
known elements into a table
by weight. He was one of the
first scientists to discover a
periodic pattern. He discovered
that by arranging the elements
by atomic mass, they shared
similar properties every 7
elements.Newlands
1864Meyer
1870Meyer published in 1870 a
periodic table. His
table displayed relationships
between atomic number and
volume. It clearly showed
connectionsbetween elements
by chemical properties.Mendeleyev
1969Mendeleyev made a periodic table
mostly based on chemical
properties of elements rather
than just atomic mass.
He also created a law that
would explain were elements
would be placed, and predicted
a few other elements that
had not been discovered
like aluminium.Moseley
1913He demonstrated
major chemical
and physical
properties are
not determined
by atomic weight
, but by atomic
number. Protons
determine
the atom's
identityThese three
creative
scientists
proposed a
3D periodic
table using
spirals that
align vertically
with other
elements
that have
similar
properties.
They aimed
for a better
education
tool to arrange
elements with
the more
possible
patterns.Seaborg
1961He identified more than
100 isotopes that were
placed in the periodic
table (with collaborators).
He also discovered
transuranium elements.
He developed the
method of isolation to
place heavy elements
in the periodic table,
known as the actinide
concept.Periods
Courtines, Gamow
and Alexander
1928-19702000 years Gap
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