element from decay
Atomic number color:
black=solid, green=liquid, red=gas
The halogens (/ˈhælədʒən, ˈheɪ-, -loʊ-, -ˌdʒɛn/)
are a group in the periodic table consisting of five chemically
related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine
(I), and astatine (At). The artificially created element 117
(tennessine, Ts) may also be a halogen. In the modern IUPAC
nomenclature, this group is known as group 17. The symbol X is often
used generically to refer to any halogen.
The name "halogen" means "salt-producing". When halogens react with
metals they produce a wide range of salts, including calcium fluoride,
sodium chloride (common table salt), silver bromide and potassium
The group of halogens is the only periodic table group that contains
elements in all three main states of matter at standard temperature
and pressure. All of the halogens form acids when bonded to hydrogen.
Most halogens are typically produced from minerals or salts. The
middle halogens, that is chlorine, bromine and iodine, are often used
as disinfectants. Organobromides are the most important class of flame
retardants. Elemental halogens are dangerous and can potentially be
Diatomic halogen molecules
184.108.40.206 Organohalogen compounds
220.127.116.11 Polyhalogenated compounds
18.104.22.168 Reactions with water
2.2 Physical and atomic
5 Biological role
8 See also
11 Further reading
The fluorine mineral fluorospar was known as early as 1529. Early
chemists realized that fluorine compounds contain an undiscovered
element, but were unable to isolate it. In 1860, George Gore, an
English chemist, ran a current of electricity through hydrofluoric
acid and probably produced fluorine, but he was unable to prove his
results at the time. In 1886, Henri Moissan, a chemist in Paris,
performed electrolysis on potassium bifluoride dissolved in anhydrous
hydrogen fluoride, and successfully isolated fluorine.
Hydrochloric acid was known to alchemists and early chemists. However,
elemental chlorine was not produced until 1774, when Carl Wilhelm
Scheele heated hydrochloric acid with manganese dioxide. Scheele
called the element "dephlogisticated muriatic acid", which is how
chlorine was known for 33 years. In 1807,
Humphry Davy investigated
chlorine and discovered that it is an actual element.
used as a poison gas during World War I.
Bromine was discovered in the 1820s by Antoine-Jérôme Balard. Balard
discovered bromine by passing chlorine gas through a sample of brine.
He originally proposed the name muride for the new element, but the
French Academy changed the element's name to bromine.
Iodine was discovered by Bernard Courtois, who was using seaweed ash
as part of a process for saltpeter manufacture. Courtois typically
boiled the seaweed ash with water to generate potassium chloride.
However, in 1811, Courtois added sulfuric acid to his process, and
found that his process produced purple fumes that condensed into black
crystals. Suspecting that these crystals were a new element, Courtois
sent samples to other chemists for investigation.
Iodine was proven to
be a new element by Joseph Gay-Lussac.
Fred Allison claimed to have discovered element 85 with a
magneto-optical machine, and named the element Alabamine, but was
mistaken. In 1937, Rajendralal De claimed to have discovered element
85 in minerals, and called the element dakine, but he was also
mistaken. An attempt at discovering element 85 in 1939 by Horia
Yvette Cauchois via spectroscopy was also unsuccessful, as
was an attempt in the same year by Walter Minder, who discovered an
iodine-like element resulting from beta decay of polonium. Element 85,
now named astatine, was produced successfully in 1940 by Dale R.
Corson, K.R. Mackenzie, and Emilio G. Segrè, who bombarded bismuth
with alpha particles.
In 1811, the German chemist Johann Salomo Christoph Schweigger
proposed that the name "halogen" – meaning "salt producer", from
αλς [als] "salt" and γενειν [genein] "to beget" – replace
the name "chlorine", which had been proposed by the English chemist
Humphry Davy. Davy's name for the element prevailed. However, in
1826, the Swedish chemist Baron
Jöns Jakob Berzelius
Jöns Jakob Berzelius proposed the
term "halogen" for the elements fluorine, chlorine, and iodine, which
produce a sea-salt-like substance when they form a compound with an
Fluorine's name comes from the
Latin word fluere, meaning "to flow",
because it was derived from the mineral fluorospar, which was used as
a flux in metal working. Chlorine's name comes from the Greek word
chloros, meaning "greenish-yellow". Bromine's name comes from the
Greek word bromos, meaning "stench". Iodine's name comes from the
Greek word iodes, meaning "violet". Astatine's name comes from the
Greek word astatos, meaning "unstable".
Tennessine is named after
the US state of Tennessee.
The halogens show trends in chemical bond energy moving from top to
bottom of the periodic table column with fluorine deviating slightly.
(It follows trend in having the highest bond energy in compounds with
other atoms, but it has very weak bonds within the diatomic F2
molecule.) This means, as you go down the periodic table, the
reactivity of the element will decrease because of the increasing size
of the atoms.
Halogen bond energies (kJ/mol)
Halogens are highly reactive, and as such can be harmful or lethal to
biological organisms in sufficient quantities. This high reactivity is
due to the high electronegativity of the atoms due to their high
effective nuclear charge. Because the halogens have seven valence
electrons in their outermost energy level, they can gain an electron
by reacting with atoms of other elements to satisfy the octet rule.
Fluorine is one of the most reactive elements, attacking
otherwise-inert materials such as glass, and forming compounds with
the usually inert noble gases. It is a corrosive and highly toxic gas.
The reactivity of fluorine is such that, if used or stored in
laboratory glassware, it can react with glass in the presence of small
amounts of water to form silicon tetrafluoride (SiF4). Thus, fluorine
must be handled with substances such as Teflon (which is itself an
organofluorine compound), extremely dry glass, or metals such as
copper or steel, which form a protective layer of fluoride on their
The high reactivity of fluorine allows paradoxically some of the
strongest bonds possible, especially to carbon. For example, Teflon is
fluorine bonded with carbon and is extremely resistant to thermal and
chemical attack and has a high melting point.
Diatomic halogen molecules
The halogens form homonuclear diatomic molecules (not proven for
astatine). Due to relatively weak intermolecular forces, chlorine and
fluorine form part of the group known as "elemental gases".
d(X−X) / pm
d(X−X) / pm
The elements become less reactive and have higher melting points as
the atomic number increases. The higher melting points are caused by
stronger London dispersion forces resulting from more electrons.
All of the halogens have been observed to react with hydrogen to form
hydrogen halides. For fluorine, chlorine, and bromine, this reaction
is in the form of:
H2 + X2 → 2HX
However, hydrogen iodide and hydrogen astatide can split back into
their constituent elements.
The hydrogen-halogen reactions get gradually less reactive toward the
heavier halogens. A fluorine-hydrogen reaction is explosive even when
it is dark and cold. A chlorine-hydrogen reaction is also explosive,
but only in the presence of light and heat. A bromine-hydrogen
reaction is even less explosive; it is explosive only when exposed to
Iodine and astatine only partially react with hydrogen,
All halogens form binary compounds with hydrogen known as the hydrogen
halides: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen
bromide (HBr), hydrogen iodide (HI), and hydrogen astatide (HAt). All
of these compounds form acids when mixed with water.
is the only hydrogen halide that forms hydrogen bonds. Hydrochloric
acid, hydrobromic acid, hydroiodic acid, and hydroastatic acid are all
strong acids, but hydrofluoric acid is a weak acid.
All of the hydrogen halides are irritants.
Hydrogen fluoride and
hydrogen chloride are highly acidic.
Hydrogen fluoride is used as an
industrial chemical, and is highly toxic, causing pulmonary edema and
Hydrogen chloride is also a dangerous chemical.
Breathing in gas with more than fifty parts per million of hydrogen
chloride can cause death in humans.
Hydrogen bromide is even more
toxic and irritating than hydrogen chloride. Breathing in gas with
more than thirty parts per million of hydrogen bromide can be lethal
Hydrogen iodide, like other hydrogen halides, is
All the halogens are known to react with sodium to form sodium
fluoride, sodium chloride, sodium bromide, sodium iodide, and sodium
astatide. Heated sodium's reaction with halogens produces
bright-orange flames. Sodium's reaction with chlorine is in the form
2Na + Cl2 → 2NaCl
Iron reacts with fluorine, chlorine, and bromine to form Iron(III)
halides. These reactions are in the form of:
2Fe + 3X2 → 2FeX3
However, when iron reacts with iodine, it forms only iron(II) iodide.
Iron wool can react rapidly with fluorine to form the white compound
iron(III) fluoride even in cold temperatures. When chlorine comes into
contact with heated iron, they react to form the black iron (III)
chloride. However, if the reaction conditions are moist, this reaction
will instead result in a reddish-brown product.
Iron can also react
with bromine to form iron(III) bromide. This compound is reddish-brown
in dry conditions. Iron's reaction with bromine is less reactive than
its reaction with fluorine or chlorine. Hot iron can also react with
iodine, but it forms iron(II) iodide. This compound may be gray, but
the reaction is always contaminated with excess iodine, so it is not
known for sure. Iron's reaction with iodine is less vigorous than its
reaction with the lighter halogens.
Main article: Interhalogen
Interhalogen compounds are in the form of XYn where X and Y are
halogens and n is one, three, five, or seven.
contain at most two different halogens. Large interhalogens, such as
ClF3 can be produced by a reaction of a pure halogen with a smaller
interhalogen such as ClF. All interhalogens except IF7 can be produced
by directly combining pure halogens in various conditions.
Interhalogens are typically more reactive than all diatomic halogen
molecules except F2 because interhalogen bonds are weaker. However,
the chemical properties of interhalogens are still roughly the same as
those of diatomic halogens. Many interhalogens consist of one or more
atoms of fluorine bonding to a heavier halogen.
Chlorine can bond with
up to 3 fluorine atoms, bromine can bond with up to five fluorine
atoms, and iodine can bond with up to seven fluorine atoms. Most
interhalogen compounds are covalent gases. However, there are some
interhalogens that are liquids, such as BrF3, and many
iodine-containing interhalogens are solids.
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Many synthetic organic compounds such as plastic polymers, and a few
natural ones, contain halogen atoms; these are known as halogenated
compounds or organic halides.
Chlorine is by far the most abundant of
the halogens in seawater, and the only one needed in relatively large
amounts (as chloride ions) by humans. For example, chloride ions play
a key role in brain function by mediating the action of the inhibitory
transmitter GABA and are also used by the body to produce stomach
Iodine is needed in trace amounts for the production of thyroid
hormones such as thyroxine. Organohalogens are also synthesized
through the nucleophilic abstraction reaction.
Polyhalogenated compounds are industrially created compounds
substituted with multiple halogens. Many of them are very toxic and
bioaccumulate in humans, and have a very wide application range. They
include PCBs, PBDEs, and perfluorinated compounds (PFCs), as well as
numerous other compounds.
Reactions with water
Fluorine reacts vigorously with water to produce oxygen (O2) and
hydrogen fluoride (HF):
2 F2(g) + 2 H2O(l) → O2(g) + 4 HF(aq)
Chlorine has maximum solubility of ca. 7.1 g Cl2 per kg of water at
ambient temperature (21 °C). Dissolved chlorine reacts to
form hydrochloric acid (HCl) and hypochlorous acid, a solution that
can be used as a disinfectant or bleach:
Cl2(g) + H2O(l) → HCl(aq) + HClO(aq)
Bromine has a solubility of 3.41 g per 100 g of water, but it
slowly reacts to form hydrogen bromide (HBr) and hypobromous acid
Br2(g) + H2O(l) → HBr(aq) + HBrO(aq)
Iodine, however, is minimally soluble in water (0.03 g/100 g water at
20 °C) and does not react with it. However, iodine will form
an aqueous solution in the presence of iodide ion, such as by addition
of potassium iodide (KI), because the triiodide ion is formed.
Physical and atomic
The table below is a summary of the key physical and atomic properties
of the halogens. Data marked with question marks are either uncertain
or are estimations partially based on periodic trends rather than
Standard atomic weight
(g/cm3at 25 °C)
First ionization energy
[35.446; 35.457][n 2]
Fluorine has one stable and naturally occurring isotope, fluorine-19.
However, there are trace amounts in nature of the radioactive isotope
fluorine-23, which occurs via cluster decay of protactinium-231. A
total of eighteen isotopes of fluorine have been discovered, with
atomic masses ranging from 14 to 31.
Chlorine has two stable and
naturally occurring isotopes, chlorine-35 and chlorine-37. However,
there are trace amounts in nature of the isotope chlorine-36, which
occurs via spallation of argon-36. A total of 24 isotopes of chlorine
have been discovered, with atomic masses ranging from 28 to 51.
There are two stable and naturally occurring isotopes of bromine,
bromine-79 and bromine-81. A total of 32 isotopes of bromine have been
discovered, with atomic masses ranging 67 to 98. There is one stable
and naturally occurring isotope of iodine, iodine-127. However, there
are trace amounts in nature of the radioactive isotope iodine-129,
which occurs via spallation and from the radioactive decay of uranium
in ores. Several other radioactive isotopes of iodine have also been
created naturally via the decay of uranium. A total of 38 isotopes of
iodine have been discovered, with atomic masses ranging from 108 to
There are no stable isotopes of astatine. However, there are three
naturally occurring radioactive isotopes of astatine produced via
radioactive decay of uranium, neptunium, and plutonium. These isotopes
are astatine-215, astatine-217, and astatine-219. A total of 31
isotopes of astatine have been discovered, with atomic masses ranging
from 193 to 223.
Approximately six million metric tons of the fluorine mineral fluorite
are produced each year. Four hundred-thousand metric tons of
hydrofluoric acid are made each year.
Fluorine gas is made from
hydrofluoric acid produced as a by-product in phosphoric acid
manufacture. Approximately 15,000 metric tons of fluorine gas are made
The mineral halite is the mineral that is most commonly mined for
chlorine, but the minerals carnallite and sylvite are also mined for
chlorine. Forty million metric tons of chlorine are produced each year
by the electrolysis of brine.
Approximately 450,000 metric tons of bromine are produced each year.
Fifty percent of all bromine produced is produced in the United
States, 35% in Israel, and most of the remainder in China.
Historically, bromine was produced by adding sulfuric acid and
bleaching powder to natural brine. However, in modern times, bromine
is produced by electrolysis, a method invented by Herbert Dow. It is
also possible to produce bromine by passing chlorine through seawater
and then passing air through the seawater.
In 2003, 22,000 metric tons of iodine were produced. Chile produces
40% of all iodine produced,
Japan produces 30%, and smaller amounts
are produced in
Russia and the United States. Until the 1950s, iodine
was extracted from kelp. However, in modern times, iodine is produced
in other ways. One way that iodine is produced is by mixing sulfur
dioxide with nitrate ores, which contain some iodates.
Iodine is also
extracted from natural gas fields.
Even though astatine is naturally occurring, it is usually produced by
bombarding bismuth with alpha particles.
From left to right: chlorine, bromine, and iodine at room temperature.
Chlorine is a gas, bromine is a liquid, and iodine is a solid.
Fluorine could not be included in the image due to its high
reactivity, and astatine due to its radioactivity.
Both chlorine and bromine are used as disinfectants for drinking
water, swimming pools, fresh wounds, spas, dishes, and surfaces. They
kill bacteria and other potentially harmful microorganisms through a
process known as sterilization. Their reactivity is also put to use in
Sodium hypochlorite, which is produced from chlorine, is
the active ingredient of most fabric bleaches, and chlorine-derived
bleaches are used in the production of some paper products. Chlorine
also reacts with sodium to create sodium chloride, which is table
Halogen lamps are a type of incandescent lamp using a tungsten
filament in bulbs that have a small amounts of a halogen, such as
iodine or bromine added. This enables the production of lamps that are
much smaller than non-halogen incandescent lightbulbs at the same
wattage. The gas reduces the thinning of the filament and blackening
of the inside of the bulb resulting in a bulb that has a much greater
Halogen lamps glow at a higher temperature (2800 to 3400
kelvins) with a whiter color than other incandescent bulbs. However,
this requires bulbs to be manufactured from fused quartz rather than
silica glass to reduce breakage.
In drug discovery, the incorporation of halogen atoms into a lead drug
candidate results in analogues that are usually more lipophilic and
less water-soluble. As a consequence, halogen atoms are used to
improve penetration through lipid membranes and tissues. It follows
that there is a tendency for some halogenated drugs to accumulate in
The chemical reactivity of halogen atoms depends on both their point
of attachment to the lead and the nature of the halogen. Aromatic
halogen groups are far less reactive than aliphatic halogen groups,
which can exhibit considerable chemical reactivity. For aliphatic
carbon-halogen bonds, the C-F bond is the strongest and usually less
chemically reactive than aliphatic C-H bonds. The other
aliphatic-halogen bonds are weaker, their reactivity increasing down
the periodic table. They are usually more chemically reactive than
aliphatic C-H bonds. As a consequence, the most common halogen
substitutions are the less reactive aromatic fluorine and chlorine
Fluoride anions are found in ivory, bones, teeth, blood, eggs, urine,
and hair of organisms. Fluoride anions in very small amounts may be
essential for humans. There are 0.5 milligrams of fluorine per
liter of human blood. Human bones contain 0.2 to 1.2% fluorine. Human
tissue contains approximately 50 parts per billion of fluorine. A
typical 70-kilogram human contains 3 to 6 grams of fluorine.
Chloride anions are essential to a large number of species, humans
included. The concentration of chlorine in the dry weight of cereals
is 10 to 20 parts per million, while in potatoes the concentration of
chloride is 0.5%. Plant growth is adversely affected by chloride
levels in the soil falling below 2 parts per million. Human blood
contains an average of 0.3% chlorine. Human bone typically contains
900 parts per million of chlorine. Human tissue contains approximately
0.2 to 0.5% chlorine. There is a total of 95 grams of chlorine in a
typical 70-kilogram human.
Some bromine in the form of the bromide anion is present in all
organisms. A biological role for bromine in humans has not been
proven, but some organisms contain organobromine compounds. Humans
typically consume 1 to 20 milligrams of bromine per day. There are
typically 5 parts per million of bromine in human blood, 7 parts per
million of bromine in human bones, and 7 parts per million of bromine
in human tissue. A typical 70-kilogram human contains 260 milligrams
Humans typically consume less than 100 micrograms of iodine per day.
Iodine deficiency can cause intellectual disability. Organoiodine
compounds occur in humans in some of the glands, especially the
thyroid gland, as well as the stomach, epidermis, and immune system.
Foods containing iodine include cod, oysters, shrimp, herring,
lobsters, sunflower seeds, seaweed, and mushrooms. However, iodine is
not known to have a biological role in plants. There are typically
0.06 milligrams per liter of iodine in human blood, 300 parts per
billion of iodine in human bones, and 50 to 700 parts per billion of
iodine in human tissue. There are 10 to 20 milligrams of iodine in a
typical 70-kilogram human.
Astatine has no biological role.
The halogens tend to decrease in toxicity towards the heavier
Fluorine gas is extremely toxic; breathing in fluorine at a
concentration of 25 parts per million is potentially lethal.
Hydrofluoric acid is also toxic, being able to penetrate skin and
cause highly painful burns. In addition, fluoride anions are toxic,
but not as toxic as pure fluorine. Fluoride can be lethal in amounts
of 5 to 10 grams. Prolonged consumption of fluoride above
concentrations of 1.5 mg/L is associated with a risk of dental
fluorosis, an aesthetic condition of the teeth. At concentrations
above 4 mg/L, there is an increased risk of developing skeletal
fluorosis, a condition in which bone fractures become more common due
to the hardening of bones. Current recommended levels in water
fluoridation, a way to prevent dental caries, range from 0.7 to
1.2 mg/L to avoid the detrimental effects of fluoride while at
the same time reaping the benefits. People with levels between
normal levels and those required for skeletal fluorosis tend to have
symptoms similar to arthritis.
Chlorine gas is highly toxic. Breathing in chlorine at a concentration
of 3 parts per million can rapidly cause a toxic reaction. Breathing
in chlorine at a concentration of 50 parts per million is highly
dangerous. Breathing in chlorine at a concentration of 500 parts per
million for a few minutes is lethal. Breathing in chlorine gas is
Hydrochloric acid is a dangerous chemical.
Pure bromine is somewhat toxic, but less toxic than fluorine and
chlorine. One hundred milligrams of bromine is lethal. Bromide
anions are also toxic, but less so than bromine. Bromide has a lethal
dose of 30 grams.
Iodine is somewhat toxic, being able to irritate the lungs and eyes,
with a safety limit of 1 milligram per cubic meter. When taken orally,
3 grams of iodine can be lethal. Iodide anions are mostly nontoxic,
but these can also be deadly if ingested in large amounts.
Astatine is very radioactive and thus highly dangerous, but it has not
been produced in macroscopic quantities and hence it is most unlikely
that its toxicity will be of much relevance to the average
Main article: Superatom
Certain aluminium clusters have superatom properties. These aluminium
clusters are generated as anions (Al−
n with n = 1, 2, 3, ... ) in helium gas and reacted with a gas
containing iodine. When analyzed by mass spectrometry one main
reaction product turns out to be Al
13I−. These clusters of 13 aluminium atoms with an extra
electron added do not appear to react with oxygen when it is
introduced in the same gas stream. Assuming each atom liberates its 3
valence electrons, this means 40 electrons are present, which is one
of the magic numbers for sodium and implies that these numbers are a
reflection of the noble gases.
Calculations show that the additional electron is located in the
aluminium cluster at the location directly opposite from the iodine
atom. The cluster must therefore have a higher electron affinity for
the electron than iodine and therefore the aluminium cluster is called
a superhalogen (i.e., the vertical electron detachment energies of the
moieties that make up the negative ions are larger than those of any
halogen atom). The cluster component in the Al
13I− ion is similar to an iodide ion or a bromide ion. The related
2 cluster is expected to behave chemically like the triiodide
Look up halogen in Wiktionary, the free dictionary.
^ The number given in parentheses refers to the measurement
uncertainty. This uncertainty applies to the least significant
figure(s) of the number prior to the parenthesized value (i.e.,
counting from rightmost digit to left). For instance,
7000100794000000000♠1.00794(7) stands for
7000100794000000000♠1.00794(72) stands for
^ The average atomic weight of this element changes depending on the
source of the chlorine, and the values in brackets are the upper and
^ The element does not have any stable nuclides, and the value in
brackets indicates the mass number of the longest-lived isotope of the
^ Jones, Daniel (2003) , Peter Roach, James Hartmann and Jane
Setter, eds., English Pronouncing Dictionary, Cambridge: Cambridge
University Press, ISBN 3-12-539683-2 CS1 maint: Uses editors
Dictionary.com Unabridged. Random House.
^ a b c d e f g h i j k l m n o p q r s t u v w x y Emsley, John
(2011). Nature's Building Blocks. ISBN 0199605637.
^ Schweigger, J.S.C. (1811). "Nachschreiben des Herausgebers, die neue
Nomenclatur betreffend" [Postscript of the editor concerning the new
nomenclature]. Journal für Chemie und Physik (in German). 3 (2):
249–255. On p. 251, Schweigger proposed the word "halogen":
"Man sage dafür lieber mit richter Wortbildung
Halogen (da schon in
der Mineralogie durch Werner's Halit-Geschlecht dieses Wort nicht
fremd ist) von αλς Salz und dem alten γενειν (dorisch
γενεν) zeugen." (One should say instead, with proper morphology,
"halogen" (this word is not strange since [it's] already in mineralogy
via Werner's "halite" species) from αλς [als] "salt" and the old
γενειν [genein] (Doric γενεν) "to beget".)
^ Snelders, H. A. M. (1971). "J. S. C. Schweigger: His Romanticism and
His Crystal Electrical Theory of Matter". Isis. 62 (3): 328.
doi:10.1086/350763. JSTOR 229946.
^ In 1826, Berzelius coined the terms Saltbildare (salt-formers) and
Corpora Halogenia (salt-making substances) for the elements chlorine,
iodine, and fluorine. See: Berzelius, Jacob (1826). Årsberättelser
om Framstegen i Physik och Chemie [Annual Report on Progress in
Physics and Chemistry] (in Swedish). vol. 6. Stockholm, Sweden: P.A.
Norstedt & Söner. p. 187. From p. 187: "De förre af
dessa, d. ä. de electronegativa, dela sig i tre klasser: 1) den
första innehåller kroppar, som förenade med de electropositiva,
omedelbart frambringa salter, hvilka jag derför kallar Saltbildare
(Corpora Halogenia). Desse utgöras af chlor, iod och fluor *)." (The
first of them [i.e., elements], the electronegative [ones], are
divided into three classes: 1) The first includes substances which,
[when] united with electropositive [elements], immediately produce
salts, and which I therefore name "salt-formers" (salt-producing
substances). These are chlorine, iodine, and fluorine *).)
^ The word "halogen" appeared in English as early as 1832 (or
earlier). See, for example: Berzelius, J.J. with A.D. Bache, trans.,
(1832) "An essay on chemical nomenclature, prefixed to the treatise on
chemistry," The American Journal of Science and Arts, 22:
248–276 ; see, for example p. 263.
^ Page 43, Edexcel International GCSE chemistry revision guide, Curtis
^ Greenwood & Earnshaw 1998, p. 804.
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^ Jim Clark (2002). "THE ACIDITY OF THE HYDROGEN HALIDES". Retrieved
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^ "Facts about hydrogen fluoride". 2005. Archived from the original on
2013-02-01. Retrieved February 2013 Check date values in:
Hydrogen chloride". Retrieved February 24, 2013
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^ "Poison Facts:Low Chemicals:
Hydrogen Iodid". Retrieved
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^ "Standard Uncertainty and Relative Standard Uncertainty". CODATA
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^ a b c Wieser, Michael E.; Coplen, Tyler B. (2011). "Atomic weights
of the elements 2009 (
IUPAC Technical Report)" (PDF). Pure Appl. Chem.
IUPAC. 83 (2): 359–396. doi:10.1351/PAC-REP-10-09-14. Retrieved 5
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(84th ed.). Boca Raton, FL: CRC Press.
^ Slater, J. C. (1964). "Atomic Radii in Crystals". Journal of
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^ Bonchev, Danail; Kamenska, Verginia (1981). "Predicting the
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Physical Chemistry. ACS Publications. 85 (9): 1177–86.
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^ Thomas, G. (2000). Medicinal Chemistry an Introduction. John Wiley
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^ a b Gray, Theodore (2010). The Elements.
^ Fawell, J.; Bailey, K.; Chilton, J.; Dahi, E.; Fewtrell, L.; Magara,
Y. (2006). "Guidelines and standards". Fluoride in Drinking-water
(PDF). World Health Organization. pp. 37–9.
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18-column, large cells
32-column, large cells
Janet's left step table
Extension beyond the 7th period
1 (Alkali metals)
2 (Alkaline earth metals)
18 (Noble gases)
Alkaline earth metals
Lists of metalloids by source
Platinum-group metals (PGM)
By: Abundance (in humans)
Heat of fusion
Heat of vaporization
Speed of sound
Thermal expansion coefficient
in East Asia
systematic element name
Periodic table (Large cells)
Alkaline earth metal
Atomic Number: 9
Atomic Weight: 18.9984032
Melting Point: 53.63 K
Boiling Point: 85.03 K
Specific mass: 0.001696 g/cm3
Atomic Number: 17
Atomic Weight: 35.453
Melting Point: 172.31 K
Boiling Point: 239.11 K
Specific mass: 0.003214 g/cm3
Atomic Number: 35
Atomic Weight: 79.904
Melting Point: 266.05 K
Boiling Point: 332.0 K
Specific mass: 3.122 g/cm3
Atomic Number: 53
Atomic Weight: 126.90447
Melting Point: 386.65 K
Boiling Point: 475.4 K
Specific mass: 4.93 g/cm3
Atomic Number: 85
Atomic Weight: 
Melting Point: 575.15 K
Boiling Point: 610 K
Specific mass: 7 g/cm3
Atomic Number: 117
Atomic Weight: 
Melting Point: ? 573–773 K
Boiling Point: ? 823 K
Specific mass: ? g/cm3