The halogens () are a
group in the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
consisting of five or six chemically related
elements
Element or elements may refer to:
Science
* Chemical element, a pure substance of one type of atom
* Heating element, a device that generates heat by electrical resistance
* Orbital elements, parameters required to identify a specific orbit of ...
:
fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
(F),
chlorine (Cl),
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table (halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simil ...
(Br),
iodine
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
(I),
astatine (At), and
tennessine (Ts). In the modern
IUPAC nomenclature, this group is known as group 17.
The word "halogen" means "salt former" (or "salt maker"). When halogens react with
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...
s, they produce a wide range of
salts, including
calcium fluoride,
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
(common table salt),
silver bromide and
potassium iodide.
The group of halogens is the only
periodic table group that contains elements in three of the main
states of matter at
standard temperature and pressure
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union o ...
. All of the halogens form acids when bonded to hydrogen. Most halogens are typically produced from
minerals or
salts. The middle halogens—chlorine, bromine, and iodine—are often used as
disinfectant
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
s. Organobromides are the most important class of
flame retardants, while elemental halogens are dangerous and can be toxic.
History
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
Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
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
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
on
potassium bifluoride dissolved in anhydrous
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in ...
, 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
Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cell ...
. Scheele called the element "dephlogisticated muriatic acid", which is how chlorine was known for 33 years. In 1807,
Humphry Davy
Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...
investigated chlorine and discovered that it is an actual element. Chlorine combined with hydrochloric acid, as well as sulfuric acid in certain instances created chlorine gas which was a
poisonous gas during
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
. It displaced oxygen in contaminated areas and replaced common oxygenated air with the toxic chlorine gas. The gas would burn human tissue externally and internally, especially the lungs, making breathing difficult or impossible depending on the level of contamination.
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
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
ash as part of a process for
saltpeter manufacture. Courtois typically boiled the seaweed ash with water to generate
potassium chloride
Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
. 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.
In 1931,
Fred Allison claimed to have discovered element 85 with a
magneto-optical machine
A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc. Both 130 mm (5.25 in) and 90 mm (3.5 in) form factors exist. In 1983, just a year after the introduc ...
, 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 Hulubei and
Yvette Cauchois via
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
was also unsuccessful, as was an attempt in the same year by
Walter Minder
Walter Minder (August 6, 1905 – April 1, 1992) was a Swiss mineralogist and chemist. In 1931, he became professor of radiology at the Institut du Radium at the University of Bern. He together with Alice Leigh-Smith announced the discovery of el ...
, 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
Dale Raymond Corson (April 5, 1914 – March 31, 2012) was the eighth president of Cornell University. Born in Pittsburg, Kansas, in 1914, Corson received a B.A. degree from the College of Emporia in 1934, his M.A. degree from the University ...
,
K.R. Mackenzie
Kenneth Ross MacKenzie (June 15, 1912 – July 4, 2002) together with Dale R. Corson and Emilio Segrè, synthesized the element astatine, in 1940. MacKenzie received his PhD under Ernest Lawrence at Lawrence Livermore National Laboratory. ...
, and
Emilio G. Segrè, who bombarded
bismuth with
alpha particles.
In 2010, a team led by nuclear physicist
Yuri Oganessian involving scientists from the
JINR,
Oak Ridge National Laboratory,
Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...
, and
Vanderbilt University successfully bombarded berkelium-249 atoms with calcium-48 atoms to make tennessine-294. As of 2022, it is the most recent element to be discovered.
Etymology
In 1811, the German chemist
Johann Schweigger proposed that the name "halogen" – meaning "salt producer", from αλς
als"salt" and γενειν
enein"to beget" – replace the name "chlorine", which had been proposed by the English chemist
Humphry Davy
Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for the ...
. Davy's name for the element prevailed. However, in 1826, the
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe ...
Baron
Jöns Jacob Berzelius
Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be on ...
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 alkaline metal.
The English names of these elements all have the ending
-ine. Fluorine's name comes from the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...
word ''fluere'', meaning "to flow", because it was derived from the mineral
fluorite, which was used as a
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
in metalworking. 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
Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to ...
.
Characteristics
Chemical
The halogens fluorine, chlorine, bromine, and iodine are
nonmetal
In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons in nonmetals behave differentl ...
s; the chemical properties of the two heaviest group 17 members have not been conclusively investigated. The halogens show trends in chemical bond energy moving from top to bottom of the periodic table column with fluorine deviating slightly. It follows a trend in having the highest bond energy in compounds with other atoms, but it has very weak bonds within the diatomic F
2 molecule. This means that further down group 17 in the periodic table, the reactivity of elements decreases because of the increasing size of the atoms.
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
The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The ...
.
Fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
is the most reactive of all elements; it is the only element more electronegative than oxygen, it attacks otherwise-inert materials such as glass, and it forms 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 (SiF
4). 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 surface.
The high reactivity of fluorine allows 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 attacks and has a high melting point.
Molecules
= Diatomic halogen molecules
=
The stable halogens form
homonuclear diatomic
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. Ot ...
molecules
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
.
Due to relatively weak intermolecular forces, chlorine and fluorine form part of the group known as "elemental gases".
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.
Compounds
= Hydrogen halides
=
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:
: H
2 + X
2 → 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 flames. Iodine and astatine only partially react with hydrogen, forming
equilibria.
All halogens form binary compounds with hydrogen known as the hydrogen halides:
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in ...
(HF),
hydrogen chloride (HCl),
hydrogen bromide (HBr),
hydrogen iodide
Hydrogen iodide () is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under sta ...
(HI), and
hydrogen astatide (HAt). All of these compounds form acids when mixed with water. Hydrogen fluoride is the only hydrogen halide that forms
hydrogen bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...
s. Hydrochloric acid, hydrobromic acid, hydroiodic acid, and 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
indu Indu or INDU may refer to:
* $INDU, a symbol for the Dow Jones Industrial Average
* Chandra, the Hindu moon deity
* South Asians, peoples of the South Asian background in South Asian and West Indian regions. (I.E. Indu-Chinese & Indo-Trini)
*A fil ...
strial chemical, and is highly toxic, causing
pulmonary edema and damaging cells. 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 to humans. Hydrogen iodide, like other hydrogen halides, is toxic.
= Metal halides
=
All the halogens are known to react with sodium to form
sodium fluoride,
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
,
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 of:
:
Iron reacts with fluorine, chlorine, and bromine to form Iron(III) halides. These reactions are in the form of:
:
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
Iron(III) fluoride, also known as ferric fluoride, are inorganic compounds with the formula FeF3(H2O)x where x = 0 or 3. They are mainly of interest by researchers, unlike the related iron(III) chlorides. Anhydrous iron(III) fluoride is white, whe ...
even in cold temperatures. When chlorine comes into contact with a heated iron, they react to form the black
iron (III) chloride
Iron(III) chloride is the inorganic compound with the formula . Also called ferric chloride, it is a common compound of iron in the +3 oxidation state. The anhydrous compound is a crystalline solid with a melting point of 307.6 °C. The col ...
. 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. A 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.
= Interhalogen compounds
=
Interhalogen compounds are in the form of XY
n where X and Y are halogens and n is one, three, five, or seven. Interhalogen compounds contain at most two different halogens. Large interhalogens, such as can be produced by a reaction of a pure halogen with a smaller interhalogen such as . All interhalogens except can be produced by directly combining pure halogens in various conditions.
Interhalogens are typically more reactive than all diatomic halogen molecules except F
2 because interhalogen bonds are weaker. However, the chemical properties of interhalogens are still roughly the same as those of
diatomic
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. Ot ...
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, some interhalogens are liquids, such as BrF
3, and many iodine-containing interhalogens are solids.
= Organohalogen compounds
=
Many synthetic
organic compounds such as
plastic polymers, and a few natural ones, contain halogen atoms; these are known as ''halogenated'' compounds or
organic halide
Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organo ...
s. 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
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...
function by mediating the action of the inhibitory transmitter
GABA and are also used by the body to produce stomach acid. 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
=
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
PCB
PCB may refer to:
Science and technology
* Polychlorinated biphenyl, an organic chlorine compound, now recognized as an environmental toxin and classified as a persistent organic pollutant
* Printed circuit board, a board used in electronics
* ...
s,
PBDEs, and
perfluorinated compounds (PFCs), as well as numerous other compounds.
Reactions
= Reactions with water
=
Fluorine reacts vigorously with water to produce
oxygen (O
2) and
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in ...
(HF):
:
Chlorine has maximum solubility of ca. 7.1 g Cl
2 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
A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...
or
bleach:
:
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 (HBrO):
:
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 observations.
Isotopes
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
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...
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 33 isotopes of bromine have been discovered, with atomic masses ranging from 66 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 145.
There are no stable
isotopes of astatine. However, there are four naturally occurring radioactive isotopes of astatine produced via radioactive decay of
uranium,
neptunium, and
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhib ...
. These isotopes are astatine-215, astatine-217, astatine-218, and astatine-219. A total of 31 isotopes of astatine have been discovered, with atomic masses ranging from 191 to 227.
Tennessine has only two known
synthetic radioisotope
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and prometh ...
s, tennessine-293 and tennessine-294.
Production
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
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solutio ...
manufacture. Approximately 15,000 metric tons of fluorine gas are made per year.
The mineral
halite is the mineral that is most commonly mined for chlorine, but the minerals
carnallite and
sylvite
Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades of ...
are also mined for chlorine. Forty million metric tons of chlorine are produced each year by the
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
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
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
, 35% in
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
, 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.
Tennessine is made by using a cyclotron, fusing berkelium-249 and calcium-48 to make tennessine-293 and tennessine-294.
Applications
Disinfectants
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 (microbiology), sterilization. Their reactivity is also put to use in Bleaching agent, bleaching. Sodium hypochlorite, which is produced from chlorine, is the active ingredient of most Cloth, fabric bleaches, and chlorine-derived bleaches are used in the production of some paper products. Chlorine also reacts with sodium to create
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
, which is table salt.
Lighting
Halogen lamps are a type of incandescent lamp using a tungsten filament in bulbs that have 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 life. Halogen lamps glow at a higher temperature (2800 to 3400 kelvins) with a whiter colour than other incandescent bulbs. However, this requires bulbs to be manufactured from fused quartz rather than silica glass to reduce breakage.
Drug components
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 adipose tissue.
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 groups.
Biological role
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 of bromine.
Humans typically consume less than 100 micrograms of iodine per day. Iodine deficiency can cause intellectual disability. organoiodine chemistry, Organoiodine compounds occur in humans in some of the glands, especially the thyroid gland, as well as the stomach, epidermis (skin), epidermis, and immune system. Foods containing iodine include Cod (food), cod, oysters, Shrimp (food), shrimp, Herring (food), herring, lobsters, sunflower seeds,
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
, and Edible mushroom, 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, although very scarce, has been found in micrograms in the earth.
It has no known biological role because of its high radioactivity, extreme rarity, and has a half-life of just about 8 hours for the most stable isotope.
Tennessine is purely man-made and has no other roles in nature.
Toxicity
The halogens tend to decrease in toxicity towards the heavier halogens.
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 Hydrofluoric acid burn, 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 highly painful.
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 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 individual.
Tennessine cannot be chemically investigated due to how short its half-life is, although its radioactivity would make it very dangerous.
Superhalogen
Certain aluminium clusters have superatom properties. These aluminium clusters are generated as anions ( 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 .
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 ion is similar to an iodide ion or a bromide ion. The related cluster is expected to behave chemically like the
triiodide ion.
See also
* Halogen bond
* Halogen addition reaction
* Halogen lamp
* Halogenation
* Interhalogen
* Pseudohalogen
Notes
References
Further reading
*
{{Authority control
Halogens,
Groups (periodic table)