Halogen Element

The halogen element refers to a periodic group VIIA element. Including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), strontium (At), Ishida (Ts), referred to as halogen.

They exist in nature as typical salts and are salt-forming elements. The halogen elements are all diatomic molecules, and their physical properties are changed regularly.

Halogen Definition

As the molecular weight increases, the dispersive forces between halogen molecules gradually increase, the color becomes darker, their melting points, boiling points, the density, and atomic volume also increase in turn.

Has an oxidizing halogen, fluoro simple substance oxidative strongest. The halogen element and the metal element constitute a large number of inorganic salts and also play an important role in fields such as organic synthesis.


Fluorine (F)

Covalent radius / Å:

0.72 electronic configuration: 1s2 2s2 p5

Elemental: fluorine gas, light yellow

The aqueous solution (data with the solubility of 20°C): violent reaction with water

(ie hydrofluoric acid 2F2 + 2H2O = 4HF + O2)

Silver salt: AgF, white, soluble in water

Other: K/Na + single halogen is white, liquid transparent and colorless

Fluorine gas is a pale yellow gas at normal temperature and is highly toxic.


The reaction with water immediately generates hydrofluoric acid and oxygen and burns, and at the same time, the container can be broken, and there is a danger of explosion when the amount is large. Fluorine and hydrogen fluoride (hydrofluoric acid) is highly corrosive to glass.

Fluorine is the most non-metallic element (and does not have d-orbital) and can only be -1 valence.

The reaction of elemental fluorine with a salt solution is first reacted with water, and the resulting hydrofluoric acid is then reacted with the salt, exposure to the base may cause an explosion.

The aqueous solution hydrofluoric acid is a medium strong acid.

However, it is the most stable hydrohalic acid because the fluorine atom contains a large electron affinity. If the skin sticks inadvertently, it will always erode to the bone marrow.

It is chemically active and can react with almost all elements (except inert gases such as helium and neon).

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Chlorine (Cl)

English name: Chlorine

Atomic number: 17

Relative atomic mass: 35.4527

Atomic radius / Å: 0.97

Atomic volume / cm 3 /mol: 22.7

Covalent radius / Å: 0.99

Electronic configuration: 1s 2 2s 2 p 6 3s 2 p 5

Ion Radius / Å: 1.81

  1. Elemental: chlorine: yellow green
  2. The aqueous solution (data of solubility 20 ° C): Chlorine water: yellow-green, solubility 0.09 mol / L
  3. CCl 4solution: yellow green
  4. Benzene solution: yellow green
  5. Silver salt: AgCl: white, hardly soluble in water
  6. Other: CuCl 2solid (no crystal water): brownish yellow; CuCl 2 solution: blue (forming complex is dark green); FeCl 3solution: yellow FeCl 2 solution: light green

Chlorine gas is yellow-green gas at normal temperature, soluble in water, and 1 volume of water can dissolve 2 volumes of chlorine.

It is toxic and reacts with water to form hydrochloric acid (HCl) and hypochlorous acid (HClO). Hypochlorous acid (HClO) is unstable, liberating oxygen and producing hydrochloric acid.

Hypochlorous acid is highly oxidizing and can be used for bleaching. The aqueous solution of chlorine is called chlorine water, which is unstable and decomposes into HCl and oxygen by light. Liquid chlorine is called liquid chlorine.

The HCl solution is a strong acid. There are many variables Chloro valences. Chlorine gas is strongly irritating to the lungs. Chlorine reacts with most elements. When chlorine has a strong oxidizing chlorine gas and reacts with a valence metal, it produces the highest metal chloride.

Generally speaking, the element has an increased oxidative property as its valence state increases, but the oxidizing acid oxidizing property of chlorine is HClO>HClO2 >HClO3 >HClO4.

Bromine (Br)

English name: Bromine

Atomic number: 35

Relative atomic mass: 79.904

Atomic radius / Å: 1.12

Atomic volume / cm 3 /mol: 23.5

Covalent radius / Å: 1.14

Electronic configuration: 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 5

Ion Radius / Å: 1.96

Related colors:

  1. Elemental: liquid bromine: dark reddish brown
  2. The aqueous solution (data of solubility 20 ° C): Bromine water: orange, solubility 0.21 mol / L (due to the difference in concentration may appear in the following colors: yellow, brown red (red-brown) color)
  3. CCl 4solution: orange-red
  4. Benzene solution: orange-red
  5. Alcohol solution: orange-red
  6. Silver salt: AgBr: light yellow, hardly soluble in water
  7. Other: BaBr 2solution: colorless; CuBr 2 solid: black crystal or crystalline powder; MgBr 2 solution: colorless

Liquid bromine is a deep reddish brown liquid at room temperature, soluble in water, and 100 grams of water can dissolve about 3 grams of bromine.

Very volatile, toxic, and steam strongly irritating to eyes, mucous membranes, etc. The aqueous solution is called bromine water.

The bromine element requires the seal of the storage container to have a water seal to prevent the vapor from escaping the human body.

It is oxidizing, has a variety of valences, and reacts weakly with water at room temperature to form hydrobromic acid and hypobromous acid. Heating can accelerate the reaction.

Hydrobromic acid is a strong acid that is more acidic than hydrochloric acid. Bromine is generally used in organic synthesis and the like. Can also be used for the extraction of some substances (such as iodine)

Iodine (I)

English name: Iodine

Atomic number: 53

Relative atomic mass: 126.90447

Atomic radius / Å: 1.32

Atomic volume / cm 3 / mol: 25.74

Electronic configuration: 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 d 10 5s 2 p 5

Ion Radius / Å: 2.2

Covalent radius / Å: 1.33

Related colors:

  1. Elemental: iodine simple substance: purple-black; iodine vapor; purple
  2. The aqueous solution (data of solubility 20 ° C): iodine water: brownish yellow, solubility 0.0013 mol / L

(Because of the different concentrations, the following colors may appear in the title: brownish yellow, purple (red), brown)

  1. CCl 4solution: purple
  2. Benzene solution: purple
  3. Alcohol solution: brown
  4. Silver salt: AgI: yellow, hardly soluble in water


Iodine is a purple-black solid at room temperature, which is toxic. It is easily soluble in solvents such as gasoline, ethanol, and benzene.

It is slightly soluble in water. Adding iodide can increase the solubility of iodine and accelerate the dissolution rate. 100 g of water can dissolve about 0.02 g of iodine at normal temperature. Low toxicity, weak oxidizing, and a variety of changeable prices.

Sublimation, sublimation by heating, steam is purple-red, but dark blue when there is no air. Sometimes you need to add water to seal.

Hydroiodic acid is the strongest hydrohalic acid without radioactivity and is also the strongest anaerobic acid without radioactivity.

However, the corrosivity is the weakest among all non-radio-hydrohalic acids, because the radius of the iodine atom is large, the electron affinity and electronegativity are small, and hydrogen ions are easily lost. It is reductive.

Iodine is the safest of all halogens because fluorine, chlorine, and bromine are more toxic and corrosive than iodine, while strontium is less toxic than iodine but radioactive.

However, iodine is not safe for the human body, especially iodine vapor, which can irritate the mucous membranes. Even to iodine, but also with non-toxic iodic acid salts (e.g., potassium iodate KIO₃). Therefore, all halogen elements are not safe for the human body.

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Astatine (At)

English name: Astatine

Atomic number: 85

Relative atomic mass: 209.9871

Atomic radius / Å: 0.57

Atomic volume / cm 3 / mol: 17.1

Covalent radius / Å: 0.72

Electronic configuration: 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 d 10 f 14 5s 2 p 6 d 10 6s 2 p 5

Ion Radius / Å: 1.33


Astatine (At) is extremely unstable. Astatine 210 is the longest half-life isotope with a half-life of only 8.1 hours. The content of radon in the earth’s crust is only one billion billion, which is mainly the product of automatic splitting of radium, thorium, and thorium.

Radon is a radioactive element. It is small, unstable, and difficult to gather. It has never been seen by anyone. (The metal should be stronger. The color should be deeper than iodine and maybe black solid).

But scientists have synthesized 20 kinds of isotope isotopes. The metal properties of bismuth are more pronounced than iodine and can be combined with silver to form AgAt which is extremely difficult to reduce.

Astatine generated hydrogenated bonded hydrogen astatine acid (HAt) is the strongest, most unstable hydrohalic acid, but the corrosion of all a hydrohalic acid weakest.

Ishida (Ts)

English name: Tennessine

Atomic number: 117

Atomic mass: 294

Atomic radius: unknown

Atomic volume: unknown

Covalent radius: 156-157pm (calculated)


Electronic configuration: [Radon] 5f 14 6d 10 7s 2 7p 5

Electronic layout: 2/8/18/32/32/18/7 (forecast)

First ionization energy: 742.9kJ/mol (predicted)

In 2010, the Dubna Joint Nuclear Research Institute, based in Moscow, on the outskirts of the Russian capital, successfully synthesized the new element 117, the latest super-heavy element artificially created in the laboratory.

An article describing this newly discovered paper has been accepted for publication by the Physical Review Letter.

The new element has not yet been named and is placed between the 116th and 118th elements of the periodic table, both of which have been discovered.

This extra heavy element is usually very radioactive and decays almost immediately.

However, many researchers believe that even heavier elements may occupy a “stability island” that allows overweight atoms to persist for a period of time.

The new work further supports a point of view. After conducting a radioactive decay analysis of the new elements, Yuri’s team wrote in a new paper: “Providing experimental verification for predicting the existence of the “heavy island” of overweight elements”.

The research team led by Yuri, of the United Nuclear Research Institute in Dubna, Russia, reported that calcium Ca-48 was bombarded with Berkelium-249 containing 97 protons and 152 neutrons – one with 20 protons and 28 Sub-composition of the isotope of Ca-40.

The impact produces two isotopes with 117 protons, one with 176 neutrons and the other with 177 neutrons.

In 2012, the Russian scientific research team successfully synthesized the 117 elements again, thus clearing the obstacle for the official addition of the 117 elements to the periodic table.

Although the 117th element was successfully synthesized for the first time in 2010, the International Union of Theoretical and Applied Chemistry (IUPAC) required the Dubna Joint Nuclear Research Institute to re-synthesize the element before they could formally approve it to be added to the periodic table.

A senior director of the Dubna Joint Nuclear Research Institute said that the research team has successfully completed the verification work and officially submitted the registration application for element 117 to IUPAC if successful, element 117 will be named within one year. And into the periodic table of elements.

It is reported that the Dubna Joint Nuclear Research Institute uses a particle cyclotron to bombard Berkelium 249 atoms containing 97 protons and 152 neutrons with 48 atoms of 20 protons and 28 neutrons, resulting in 6 possessions. A new atom of 117 protons, five of which have 176 neutrons and the other has 177 neutrons.

The International Chemical Society (IUPAC) finalized the 117 elements by scientists from Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, and the Joint Nuclear Research Institute of Dubha, Russia. Element 117 is named after Tennessine (abbreviation Ts) with the spelling of the English name of “Tennessee”, and the Chinese character is the new element (Ishida).

Elemental nature

Atomic structural features

The outermost electrons are the same, all of which are 7 electrons. Due to the difference in the number of electron layers, the atomic radii are different, and the radius of the atoms from F to I increases sequentially.

Therefore, the attraction ability of the nucleus to the outermost electrons is sequentially weakened and is obtained from the outside. The ability of electrons is weakened in turn, and the oxidative properties of the element are weakened.


Halogens are chemically similar. They have 7 electrons on the outermost electron layer. They have a tendency to obtain a stable halide of an octagonal structure.

Therefore, halogens are oxidizing, and the atomic radius is smaller. The stronger the oxidizing property, the fluorine is the most oxidizing substance in the elemental substance.

In addition to F, the oxidation state of halogen is +1, +3, +5, +7, forming an ionic compound with a typical metal, and other halides are covalent compounds. Halogen combines with hydrogen to form a hydrogen halide, which is soluble in water to form a hydrohalic acid.

2F 2 (g)+2H 2 O(l)=4HF(aq)+O 2 (g)

2 (g) + H 2 O (l) ⇌ HX (aq) + HXO (aq) X = represents Cl Br I

The compound formed between the halogens is called a perhalogen compound such as ClF3 (chlorine trifluoride) or ICl (chloroiodide compound).

Halogen can also form oxo acids of various valence states, such as HClO, HClO2, HClO3, HClO4. The halogen element is very stable, and halogen molecules are difficult to decompose at high temperatures except for I2.

Halogen and its compounds are used in a wide variety of applications. For example, we have to eat salt every day, mainly made of chlorine and sodium elements of chlorides, and also contains a small amount of MgCl₂.


Physical degeneration of elemental matter: from F2 to I2, the color changes from shallow to deep; the state is from gas, liquid to solid; the melting point is gradually increased; the density is gradually increased; the solubility is gradually reduced.

Elemental oxidation: F 2 >Cl 2 >Br 2 >I 2

Anion reducing property: F  <Cl  <Br  <I 

The toxicity of halogens is reduced from the beginning of F.

In addition, the chemical nature of halogens is relatively active, so halogens exist only in nature in a combined state.

The boiling point of hydride is different: HF>HI>HBr>HCl, because HF has the highest boiling point of a hydrogen bond, and other molecular weight increases with molecular weight, and the boiling point increases.


conditionSpecial phenomenonProduct stabilityChemical equation
2dark placeFierce mergervery stable2 (g) + F 2 (g) = 2HF (g)
Cl 2Light or light———————More stable2 (g) + Cl 2 (g) = 2 HCl (g) (ignited or illuminated)
Br 2heating———————Poor stability2 (g) + Br 2 (g) = 2HBr (g) (heating)
2Constant heatingSlow responseUnstable2 (g) + I 2 (g) = 2 HI (g) (continuous heating)

Conclusion: As the number of nuclear charges increases, the halogen element changes with H 2: F 2, Cl 2, Br 2, I 2

1 intensity: gradual weakening 2 stability of HX formation: different conditions of reaction with hydrogen, the stability of the resulting gas hydride is different, HF>HCl>HBr>HI.

The acidity of anaerobic acid is different: HI>HBr>HCl>HF.

Chlorine gas is hardly soluble in saturated sodium chloride solution, while iodine is easily soluble in potassium iodide solution (I – is formed )

Note: the concept of extraction and dispensing

  • What is the phenomenon of adding carbon tetrachloride to the bromine water and shaking it? (layered, the lower orange-red upper layer is colorless)
  • What is the phenomenon of adding kerosene to the iodine water and shaking it? (layered, upper layer purple, lower layer colorless)

Identification of halide ions

Add HNO3 acidified silver nitrate solution,

Chloride ion: white precipitate Ag + (aq) + Cl  (aq) – → AgCl (s)

Bromide ion: pale yellow precipitate Ag + (aq) + Br  (aq) – → AgBr (s)

Iodide ion: yellow precipitate Ag + (aq) + I  (aq) – → AgI (s)

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