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The Element Iodine
10 Iodine Facts (Atomic Number 53 or I)
Facts about the
Element Iodine
by Anne Marie
Helmenstine, Ph.D.
Iodine is element 53 on
the periodic table, with element symbol I.
Iodine is an element you
encounter in iodized salt and some dyes.
A small amount of iodine
is essential for nutrition, while too much is toxic. Here are facts about this
interesting, colorful element.
The Name
Iodine comes from the
Greek word iodes, which means violet. Iodine
vapor is violet-colored.
The element was
discovered in 1811 by French chemist Bernard Courtois.
Courtois discovered
iodine by accident while he was making saltpeter for use in the Napoleonic
Wars.
Making saltpeter
required sodium carbonate.
To get sodium carbonate, Courtois burned seaweed, washed the ash with water,
and added sulfuric acid to remove contaminants.
Courtois discovered
adding an excess of sulfuric acid produced a cloud of purple vapor.
While Courtois believed
the vapor was a previously unknown element, he couldn't afford to research it,
so he offered samples of the gas to his friends, Charles Bernard Desormes and
Nicolas Clement.
They characterized the
new material and made Courtois' discovery public.
Isotopes
Many isotopes of
iodine are known. All of them are radioactive except for I-127, which is the
only isotope found in nature.
Because there is only one
natural isotope of iodine, its atomic weight is precisely known, rather than an
average of isotopes like most elements.
Color and Other Properties
Iodine is element 53 on the
periodic table, with element symbol I.
Iodine is an element you encounter
in iodized salt and some dyes.
A small amount of iodine is
essential for nutrition, while too much is toxic. Here are facts about this
interesting, colorful element.
The Name
Iodine comes from the Greek
word iodes, which means violet. Iodine vapor is
violet-colored.
The element was discovered in
1811 by French chemist Bernard Courtois.
Courtois discovered iodine by
accident while he was making saltpeter for use in the Napoleonic Wars.
Making saltpeter
required sodium carbonate. To get sodium carbonate,
Courtois burned seaweed, washed the ash with water, and added sulfuric acid to
remove contaminants.
Courtois discovered adding an
excess of sulfuric acid produced a cloud of purple vapor.
While Courtois believed the
vapor was a previously unknown element, he couldn't afford to research it, so
he offered samples of the gas to his friends, Charles Bernard Desormes and
Nicolas Clement.
They characterized the new
material and made Courtois' discovery public.
Isotopes
Many isotopes of iodine are known. All of
them are radioactive except for I-127, which is the only isotope found in
nature.
Because there is only one
natural isotope of iodine, its atomic weight is precisely known, rather than an
average of isotopes like most elements.
Color and Other Properties
Solid iodine is blue-black in
color, with a metallic sheen.
At ordinary temperatures and
pressures, iodine sublimates into its violet gas, so the liquid form is not
seen.
The color of iodine follows a
trend seen in the halogens: they appear progressively darker as you move down
the group of the periodic table.
This trend happens because the
wavelengths of light absorbed by the elements increases due to the behavior of
the electrons.
Iodine is slightly soluble in
water and more soluble in nonpolar solvents. Its melting point and boiling
point are the highest of the halogens.
The bond between atoms in
the diatomic molecule is the weakest in the
element group.
Halogen
Iodine is a halogen, which is a type of non-metal. It is
located beneath fluorine, chlorine, and bromine on the periodic table, making
it the heaviest stable element in the halogen group.
Thyroid
The thyroid gland uses iodine to make the
hormones thyroxine and triiodotyronine.
Insufficient iodine leads to
development of a goiter, which is a swelling of the thyroid gland.
Iodine deficiency is believed
to be the leading preventable cause of mental retardation.
Excessive iodine symptoms are
similar to those of iodine insufficiency.
Iodine toxicity is more severe
if a person has a selenium deficiency.
Compounds
Iodine occurs in compounds
and as the diatomic molecule I2.
Medical Purpose
Iodine is used extensively in
medicine. However, some people develop a chemical sensitivity to iodine.
Sensitive individuals may
develop a rash when swabbed with tincture of iodine.
In rare cases, anaphylactic
shock has resulted from medical exposure to iodine. Potassium iodide is used
in radiation pills.
Food Source
Natural food sources of iodine
are seafood, kelp and plants grown in iodine-rich soil. Potassium iodide often
is added to table salt to produce iodized salt.
Atomic Number
The atomic number of iodine is 53, meaning all atoms of iodine possess 53
protons.
Commercial Source
Commercially, iodine is mined
in Chile and extracted from iodine-rich brine, notably from the oilfields in
the US and Japan. Prior to this, iodine was extracted from kelp.
Iodine Element Fast Facts
· Element Name: Iodine
· Element Symbol: I
· Atomic Number: 53
· Atomic Weight: 126.904
· Group: Group 17 (Halogens)
· Period: Period 5
· Appearance: Metallic blue-black solid; violet gas
· Electron Configuration: [Kr] 4d10 5s2 5p5
· Melting Point: 386.85 K (113.7 °C, 236.66 °F)
· Boiling Point: 457.4 K (184.3 °C, 363.7 °F)
Anne
Marie Helmenstine, Ph.D.
Chemistry
Expert
Education
Ph.D.,
Biomedical Sciences, University of Tennessee at Knoxville
B.A.,
Physics and Mathematics, Hastings College
Introduction
Ph.D.
in biomedical sciences from the University of Tennessee at Knoxville - Oak
Ridge National Laboratory.
Science
educator with experience teaching chemistry, biology, astronomy, and
physics at the high school, college, and graduate levels.
ThoughtCo
and About Education chemistry expert since 2001.
Widely-published
graphic artist, responsible for printable periodic tables and other
illustrations used in science.
Experience
Anne
Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education
since 2001, and other sciences since 2013. She taught chemistry, biology,
astronomy, and physics at the high school, college, and graduate levels.
She has worked as a research scientist and also abstracting and indexing
diverse scientific literature for the Department of Energy.
In
addition to her work as a science writer, Dr. Helmenstine currently serves as a
scientific consultant, specializing in problems requiring an interdisciplinary
approach. Previously, she worked as a research scientist and college professor.
Education
Dr.
Helmenstine holds a Ph.D. in biomedical sciences from the University of
Tennessee at Knoxville and a B.A. in physics and mathematics with a minor
in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine
developed ultra-sensitive chemical detection and medical diagnostic tests.
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