PERIODIC TABLE
EVERYTHING
WORTH
KNOWING
36 DISCOVERMAGAZINE.COM
The First Periodic Table
Scientists had long created rudimentary tables of the known ele-
ments, but 150 years ago, a Russian chemist granted the modern
table its power. In 1869, Dmitri Mendeleev established what we
now call the periodic law: Specific trends, such as melting point
and atomic radius, recur periodically among the elements when
they’re listed in order of increasing atomic weight. End a row
and start a new one when that pattern starts over, and you’ll get
something quite similar to the current periodic table, where
columns represent shared traits.
But, crucially, Mendeleev wasn’t a huge stickler for his own
rules. He left gaps in his table where he felt undiscovered
elements might lie, even predicting (correctly) some of their
attributes. And he would sometimes fudge the arrangement
to keep like elements together, even if they were technically
out of order. As it turns out, chemists learned in the early 20th
century that the true order of the elements is dictated not by
atomic weight, but by the number of protons in an element’s
nucleus — an insight that resulted in only minute changes to
the table, thanks to Mendeleev’s fudges.
By now, scientists have filled in all those gaps in the table. The
latest elements were discovered only 12 years ago, and we’re cur-
rently on the hunt for even more, hoping to start a whole new row.
Who Picks the Names and
Symbols of New Elements?
The discoverers do — as long as the International
Union of Pure and Applied Chemistry (IUPAC) approves.
The IUPAC usually suggests the name end in -ium
for consistency, and past practice has been to honor
places (americium and polonium), people (curium
and einsteinium) and even planets (uranium and
plutonium). Before an element is officially named, its
placeholder name is based on the Latin names for its
atomic number: oganesson, number 118, was known as
ununoctium (one-one-eight-ium).
Are There
Other Tables?
While the familiar
rectangle is the
most iconic and
standard version of
the periodic table,
other organizational
schemes exist, such
as the ADOMAH
table (right),
which emphasizes
electron shapes,
and Otto Theodor
Benfey’s spiral table
(below), which is
more compact and
continuous.
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Dmitri Mendeleev
conceived of the
modern periodic
table 150 years ago.