84
Po
Polonium
(209)
1H
Hydrogen
1.008
43
Tc
Technetium
(98)
JULY/AUGUST 2019. DISCOVER 35
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The lanthanide and actinide series — those two
rows floating by themselves, named after their
first members, lanthanum and actinium — are
isolated like that as a concession to limited space.
They truly belong wedged in among the other
elements, but the full uninterrupted table would
be too unwieldy and take up too much room.
Technetium was just a gap in the periodic
table for decades, frustrating chemists
who tried to find it. Like most elements,
technetium can be forged in the furnaces
of stars, but it doesn’t stick around long
enough for us to stumble upon any. When
at last Italian researchers Carlo Perrier
and Emilio Segrè isolated a sample,
it was only because another science
experiment had created some via nuclear
reactions. The name comes from the
Greek word for artificial, technētos.
The general shape of the periodic table might
look uneven, but it reflects the crazy way
electrons orbit around atomic nuclei. Theydon’t go around in nice, neat circles, like
planets around the sun; instead, electrons
scatter into shapes called orbitals, which
depend on how many other electrons are in
the vicinity. For example, the first two columns
include the sphere-shaped s orbitals, which can
contain up to two electrons; the large block of
columns from boron to neon groups elements
with variations of dumbbell-shaped p orbitals.
Hydrogen is a bit of an
oddball, unique among
elements with no close
analog. Some tables thus
have it sitting alone, but
most include it in the alkali
metal group because, like
them, it has one electron.
Starting with element 84,
polonium in the table,
all naturally occurring
elements are radioactive,
meaning they’re unstable
and emit energy.
84
Po
Polonium
(209)
1H
43
Tc
s
p 1p 2
p 3