Halogen
The halogens (/ˈhælədʒən, ˈheɪ-, -loʊ-, -ˌdʒɛn/[1][2][3]) are a group in the periodic table consisting of six ch
related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine
tennessine (Ts), though some authors[4] would exclude tennessine as its chemistry is unknown and is theo
expected to be more like that of gallium. 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 metals, they produce a wi
of salts, including calcium fluoride, sodium chloride (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 m
standard temperature and pressure, though not far above room temperature the same becomes true of groups
assuming white phosphorus is taken as the standard state.[n 1] All of the halogens form acids when bonded to h
Most halogens are typically produced from minerals or salts. The middle halogens—chlorine, bromine, and iod
often used as disinfectants. Organobromides are the most important class of flame retardants, while elemental h
are dangerous and can be toxic.
History
The fluorine mineral fluorospar was known as early as 1529. Early chemists realized that fluorine compounds
an undiscovered element, but were unable to isolate it. In 1860, George Gore, an English chemist, ran a cu
electricity through hydrofluoric acid and probably produced fluorine, but he was unable to prove his results at t
In 1886, Henri Moissan, a chemist in Paris, performed electrolysis on potassium bifluoride dissolved in an
hydrogen fluoride, and successfully isolated fluorine.[7]
Hydrochloric acid was known to alchemists and early chemists. However, elemental chlorine was not produc
1774, when Carl Wilhelm Scheele heated hydrochloric acid with manganese dioxide. Scheele called the
"dephlogisticated muriatic acid", which is how chlorine was known for 33 years. In 1807, Humphry Davy inve
chlorine and discovered that it is an actual element. Chlorine gas was used as a poisonous gas during World W
displaced oxygen in contaminated areas and replaced common oxygenated air with the toxic chlorine gas.
would burn human tissue externally and internally, especially the lungs, making breathing difficult or im
depending on the level of contamination.[7]
Bromine was discovered in the 1820s by Antoine Jérôme Balard. Balard discovered bromine by passing chlo
through a sample of brine. He originally proposed the name muride for the new element, but the French A
changed the element's name to bromine.[7]
Iodine was discovered by Bernard Courtois, who was using seaweed ash as part of a process for saltpeter manu
Courtois typically boiled the seaweed ash with water to generate potassium chloride. However, in 1811, Courto
sulfuric acid to his process and found that his process produced purple fumes that condensed into black
Suspecting that these crystals were a new element, Courtois sent samples to other chemists for investigation. Io
proven to be a new element by Joseph Gay-Lussac.[7]
In 1931, Fred Allison claimed to have discovered element 85 with a magneto-optical machine, and named the
Alabamine, but was mistaken. In 1937, Rajendralal De claimed to have discovered element 85 in minerals, an
the element dakine, but he was also mistaken. An attempt at discovering element 85 in 1939 by Horia Hulu
Yvette Cauchois via spectroscopy was also unsuccessful, as was an attempt in the same year by Walter Mind
discovered an iodine-like element resulting from beta decay of polonium. Element 85, now named astat
produced successfully in 1940 by Dale R. Corson, K.R. Mackenzie, and Emilio G. Segrè, who bombarded bism
alpha particles.[7]
In 2010, a team led by nuclear physicist Yuri Oganessian involving scientists from the JINR, Oak Ridge
Laboratory, Lawrence Livermore National Laboratory, and Vanderbilt University successfully bombarded be
, The halogens fluorine, chlorine, bromine, and iodine are nonmetals; the chemical properties of the two
group 17 members have not been conclusively investigated. The halogens show trends in chemical bond energy
from top to bottom of the periodic table column with fluorine deviating slightly. It follows a trend in having
other atoms, but it has very weak bonds within the diatomic F2 molecule. This means that further down gro
elements decreases because of the increasing size of the atoms.[13]
Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quanti
This high reactivity is due to the high electronegativity of the atoms due to their high effective nuclear cha
Because the halogens have seven valence electrons in their outermost energy level, they can gain an electron
reacting with atoms of other elements to satisfy the octet rule. Fluorine is the most reactive of all elements; it is
only element more electronegative than oxygen, it attacks otherwise-inert materials such as glass, and it fo
compounds with the usually inert noble gases. It is a corrosive and highly toxic gas. The reactivity of fluorin
such that, if used or stored in laboratory glassware, it can react with glass in the presence of small amounts of w
to form silicon tetrafluoride (SiF4). Thus, fluorine must be handled with substances such as Teflon (which is i
an organofluorine compound), extremely dry glass, or metals such as copper or steel, which form a protective la
of fluoride on their surface.
The high reactivity of fluorine allows some of the strongest bonds possible, especially to carbon. For example,
extremely resistant to thermal and chemical attacks and has a high melting point.
Molecules
Diatomic halogen molecules
The stable halogens form homonuclear diatomic molecules. Due to relatively weak intermolecular forces, ch
known as "elemental gases".
d(X−X) / pm d(X−X) /
halogen molecule structure model
(gas phase) (solid pha
fluorine F2 143 149
chlorine Cl2 199 198
bromine Br2 228 227
iodine I2 266 272
The elements become less reactive and have higher melting points as the atomic number increases. The hi
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,
H2 + X2 → 2HX
However, hydrogen iodide and hydrogen astatide can split back into their constituent elements.[15]
The halogens (/ˈhælədʒən, ˈheɪ-, -loʊ-, -ˌdʒɛn/[1][2][3]) are a group in the periodic table consisting of six ch
related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine
tennessine (Ts), though some authors[4] would exclude tennessine as its chemistry is unknown and is theo
expected to be more like that of gallium. 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 metals, they produce a wi
of salts, including calcium fluoride, sodium chloride (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 m
standard temperature and pressure, though not far above room temperature the same becomes true of groups
assuming white phosphorus is taken as the standard state.[n 1] All of the halogens form acids when bonded to h
Most halogens are typically produced from minerals or salts. The middle halogens—chlorine, bromine, and iod
often used as disinfectants. Organobromides are the most important class of flame retardants, while elemental h
are dangerous and can be toxic.
History
The fluorine mineral fluorospar was known as early as 1529. Early chemists realized that fluorine compounds
an undiscovered element, but were unable to isolate it. In 1860, George Gore, an English chemist, ran a cu
electricity through hydrofluoric acid and probably produced fluorine, but he was unable to prove his results at t
In 1886, Henri Moissan, a chemist in Paris, performed electrolysis on potassium bifluoride dissolved in an
hydrogen fluoride, and successfully isolated fluorine.[7]
Hydrochloric acid was known to alchemists and early chemists. However, elemental chlorine was not produc
1774, when Carl Wilhelm Scheele heated hydrochloric acid with manganese dioxide. Scheele called the
"dephlogisticated muriatic acid", which is how chlorine was known for 33 years. In 1807, Humphry Davy inve
chlorine and discovered that it is an actual element. Chlorine gas was used as a poisonous gas during World W
displaced oxygen in contaminated areas and replaced common oxygenated air with the toxic chlorine gas.
would burn human tissue externally and internally, especially the lungs, making breathing difficult or im
depending on the level of contamination.[7]
Bromine was discovered in the 1820s by Antoine Jérôme Balard. Balard discovered bromine by passing chlo
through a sample of brine. He originally proposed the name muride for the new element, but the French A
changed the element's name to bromine.[7]
Iodine was discovered by Bernard Courtois, who was using seaweed ash as part of a process for saltpeter manu
Courtois typically boiled the seaweed ash with water to generate potassium chloride. However, in 1811, Courto
sulfuric acid to his process and found that his process produced purple fumes that condensed into black
Suspecting that these crystals were a new element, Courtois sent samples to other chemists for investigation. Io
proven to be a new element by Joseph Gay-Lussac.[7]
In 1931, Fred Allison claimed to have discovered element 85 with a magneto-optical machine, and named the
Alabamine, but was mistaken. In 1937, Rajendralal De claimed to have discovered element 85 in minerals, an
the element dakine, but he was also mistaken. An attempt at discovering element 85 in 1939 by Horia Hulu
Yvette Cauchois via spectroscopy was also unsuccessful, as was an attempt in the same year by Walter Mind
discovered an iodine-like element resulting from beta decay of polonium. Element 85, now named astat
produced successfully in 1940 by Dale R. Corson, K.R. Mackenzie, and Emilio G. Segrè, who bombarded bism
alpha particles.[7]
In 2010, a team led by nuclear physicist Yuri Oganessian involving scientists from the JINR, Oak Ridge
Laboratory, Lawrence Livermore National Laboratory, and Vanderbilt University successfully bombarded be
, The halogens fluorine, chlorine, bromine, and iodine are nonmetals; the chemical properties of the two
group 17 members have not been conclusively investigated. The halogens show trends in chemical bond energy
from top to bottom of the periodic table column with fluorine deviating slightly. It follows a trend in having
other atoms, but it has very weak bonds within the diatomic F2 molecule. This means that further down gro
elements decreases because of the increasing size of the atoms.[13]
Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quanti
This high reactivity is due to the high electronegativity of the atoms due to their high effective nuclear cha
Because the halogens have seven valence electrons in their outermost energy level, they can gain an electron
reacting with atoms of other elements to satisfy the octet rule. Fluorine is the most reactive of all elements; it is
only element more electronegative than oxygen, it attacks otherwise-inert materials such as glass, and it fo
compounds with the usually inert noble gases. It is a corrosive and highly toxic gas. The reactivity of fluorin
such that, if used or stored in laboratory glassware, it can react with glass in the presence of small amounts of w
to form silicon tetrafluoride (SiF4). Thus, fluorine must be handled with substances such as Teflon (which is i
an organofluorine compound), extremely dry glass, or metals such as copper or steel, which form a protective la
of fluoride on their surface.
The high reactivity of fluorine allows some of the strongest bonds possible, especially to carbon. For example,
extremely resistant to thermal and chemical attacks and has a high melting point.
Molecules
Diatomic halogen molecules
The stable halogens form homonuclear diatomic molecules. Due to relatively weak intermolecular forces, ch
known as "elemental gases".
d(X−X) / pm d(X−X) /
halogen molecule structure model
(gas phase) (solid pha
fluorine F2 143 149
chlorine Cl2 199 198
bromine Br2 228 227
iodine I2 266 272
The elements become less reactive and have higher melting points as the atomic number increases. The hi
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,
H2 + X2 → 2HX
However, hydrogen iodide and hydrogen astatide can split back into their constituent elements.[15]
