Germanium is a chemical element with the symbol Ge and atomic
number 32. It is a lustrous, hard, grayish-white metalloid in the
carbon group, chemically similar to its group neighbors tin and
silicon. Germanium has five naturally occurring isotopes ranging in
atomic mass number from 70 to 76. It forms a large number of
organometallic compounds, including tetraethylgermane and
isobutylgermane.
Germanium was discovered comparatively late because very few
minerals contain it in high concentration. Germanium ranks near
fiftieth in relative abundance of the elements in the Earth's
crust. In 1869, Dmitri Mendeleev predicted its existence and some
of its properties based on its position on his periodic table and
called the element eka-silicon. Nearly two decades later, in 1886,
Clemens Winkler found it in the mineral argyrodite. Winkler found
that experimental observations agreed with Mendeleev's predictions
and named the element after his country, Germany.
Germanium is an important semiconductor material used in
transistors and various other electronic devices. Its major end
uses are fiber-optic systems and infrared optics, but it is also
used for polymerization catalysts, and in electronics and solar
cell applications. It is finding a new use in nanowires.
Germanium is mined primarily from sphalerite, though it is also
recovered from silver, lead, and copper ores. Some germanium
compounds, such as germanium chloride and germane, can irritate the
eyes, skin, lungs, and throat.
In his report on The Periodic Law of the Chemical Elements, in
1869, the Russian chemist Dmitri Ivanovich Mendeleev predicted the
existence of several unknown chemical elements, including one that
would fill a gap in the carbon family in his Periodic Table of the
Elements, located between silicon and tin. Because of its position
in his Periodic Table, Mendeleev called it ekasilicon (Es), and he
estimated its atomic weight as about 72.0.
In mid-1885, at a mine near Freiberg, Saxony, a new mineral was
found. It was named argyrodite, because of its high silver (metal)
content. The chemist Clemens Winkler analyzed this new mineral, and
he was then able to isolate a new element somewhat similar to
antimony in 1886. Before Winkler published his results on the new
element, he decided that he would name his element neptunium, since
the recent discovery of planet Neptune in 1846 had been preceded by
mathematical predictions of its existence. However, the name
"neptunium" had already been given to another chemical element
(though not the element that today bears the name neptunium, which
was discovered in 1940), so instead, Winkler named the new element
germanium (from the Latin word, Germania, for Germany) in honor of
his homeland.
Because this new element showed some similarities with the
elements arsenic and antimony, its proper place in the periodic
table was under consideration, but its similarities with Dmitri
Mendeleev's predicted element "ekasilicon" confirmed that it
belonged in this place on the periodic table. With further material
from 500 kg of ore from the mines in Saxony, Winkler confirmed the
chemical properties of the new element in 1887. He also determined
an atomic weight of 72.32 by analyzing pure germanium tetrachloride
(GeCl4), while Lecoq de Boisbaudran deduced 72.3 by a comparison of
the lines in the spark spectrum of the element.
Winkler was able to prepare several new compounds of germanium,
including its fluorides, chlorides, sulfides, germanium dioxide,
and tetraethylgermane (Ge(C2H5)4), the first organogermane. The
physical data from these compounds — which corresponded well
with Mendeleev's predictions — made the discovery an
important confirmation of Mendeleev's idea of element periodicity.
Here is a comparison between the prediction and Winkler's data:
Under standard conditions germanium is a brittle, silvery-white,
semi-metallic element. This form constitutes an allotrope
technically known as a-germanium, which has a metallic luster and a
diamond cubic crystal structure, the same as diamond. At pressures
above 120 kbar, a different allotrope known as ß-germanium forms,
which has the same structure as ß-tin. Along with silicon, gallium,
bismuth, antimony, and water, it is one of the few substances that
expands as it solidifies (i.e. freezes) from its molten state.
Germanium is a semiconductor. Zone refining techniques have led
to the production of crystalline germanium for semiconductors that
has an impurity of only one part in 1010, making it one of the
purest materials ever obtained. The first metallic material
discovered (in 2005) to become a superconductor in the presence of
an extremely strong electromagnetic field was an alloy of germanium
with uranium and rhodium.
Pure germanium is known to spontaneously extrude very long screw
dislocations, referred to as germanium whiskers. The growth of
these whiskers is one of the primary reasons for the failure of
older diodes and transistors made from germanium; depending on what
they eventually touch, they may lead to an electrical short.