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Halogen Family

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The members of the seventh main group of the periodic system of the elements are commonly referred to as the halogen group. The non metallic elements are grouped together to form group 17 of the periodic table. Their salts are present in seawater and hence they are collectively known an halogens.

The group collectively is called halogen family. All halogens precede the noble gases in the periodic table because their atoms contain one electron less than the electric configuration of the inert gas. Halogen exhibit non metallic behavior. Astatine the last member of halogen family is a radioactive element with a very short life. All other halogens are abundant in nature in the combined state.

All the elements of this group have seven electrons in the outer valence shell. The s2p5 configuration is one p electron less than that of the next noble gas. The electronic configuration of all elements of halogen family are listed below.

S.No
Element
Symbol
Atomic number
Electronic configuration
1
Fluorine F 9 [He]2s22p5
2
Chlorine
Cl
17
[Ne]3s23p5
3
Bromine
Br
35
[Ar]3d104s24p5
4
Iodine
I
53
[Kr]4d105s25p5
5
Astatine
As
85 [Xe]4f145d106s26p5

The atoms of halogens complete their octet either by acquiring an electron or by sharing an electron with another atom forming covalent bond. Compounds with metals are typically ionic while with non metals are covalent.
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Halogen Compounds

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The list of halogen compounds are given below.

Alkyl halides or haloalkanes

These form a homologous series of the general formula CnH2n+1X. In these the halogen atom is bonded to an alkyl group, the C of the C-X bond is sp3 hybridized. The alkyl as already stated may be primary (1o), secondary (2o) or tertiary (3o).

Allylic halides

In these compounds, the halogen atom is bonded to sp3 - hybridized carbon atom next to an allylic carbon.

Allylic halides

Benzylic halides

In these compounds the halogen atom is bonded to sp3 hybridized carbon atom next to an aromatic ring.

Benzylic halides

Vinylic halides

In these compounds the halogen atom is bonded to sp2 hybridized carbon atom of a carbon-carbon double bond.

Vinylic halides

Aryl halides

In these compounds the halogen atom is bonded to sp2 hybridized carbon atom of an aromatic ring.

Aryl halides

Halogen Family Definition

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"A halogen is a chemical element from Group 17 of the periodic table composed of fluorine, chlorine, bromine, iodine and astatine. The man made element 117 is predicted to be a halogen."
The Swedish chemist Berzelius coined the term halogen from the Greek "hals", "salt" and "ges" meaning "come to be" - for an element that produces a salt with a metal.

Halogen Family of Elements

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Halogen family elements are listed below.
  1. Fluorine (F)
  2. Chlorine (Cl)
  3. Bromine (Br)
  4. Iodine (I)
  5. Astatine (At)
comprise group 17 of the periodic table. Collectively they are known as halogens. The anions of these elements are known as halide ions.

The halogen family elements are reactive non metals. Fluorine and chlorine are colorless gases, bromine is a red brown fuming liquid and iodine is purple black solid. All these elements have seven electrons in their valence shell. They are non conductors of heat and electricity.

Halogen on Periodic Table

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The periodic table arranges element in the increasing atomic number order. The elements of Group 17 the halogens are found on the right side of the periodic table between groups 13-16 and group 18. The halogen group periodic table is shown below.

Halogen on Periodic Table

The first member of this family is fluorine which is the most reactive and the most electronegative element known. Due to this reason it is termed as super halogen.

Periodic Properties of Elements

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Fluorine, chlorine, bromine and iodine appear in the next to last column of the periodic table. They are the halogens. In their elemental form these four elements form diatomic molecules with the formula X2.

The properties which are directly or indirectly related to their electronic configuration and which show a regular gradation when we move from left to right in a period or from top to bottom in a group are called periodic properties.
  1. Atomic radius - Atomic radius is the distance between the center of the nucleus of an atom and its outermost shell. This property seems to be increases from fluorine to iodine.
  2. Metallic character - Metallic character of an element is measured as the ease with which it loses electrons to form positive ion and it increases on moving down the group form fluorine to iodine.
  3. Electronegativity - Electronegativity is the tendency of an atom in a molecule to attract electrons towards itself. This property tends to decrease on moving down the group from fluorine to iodine.
  4. Ionization energy - Ionization energy is the energy is the energy required to remove an electron from an isolated neutral gaseous atom in its ground state. This property tends to decrease on moving down the group from fluorine to iodine.
  5. Electron affinity - electron affinity is the energy released when an electron is accepted by a neutral gaseous atom in its ground state. This property tends to decrease on moving down the group from fluorine to iodine.

Physical Properties of Halogens

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  1. Physical state - All are non metals and are diatomic in gaseous state. Under ordinary conditions fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. Non metallic character decreases from fluorine to iodine. The color also changes from fluorine to iodine.
  2. Conductivity - All are bad conductors of heat and electricity.
  3. Size of atom - They have smallest size in their period. Atomic size decreases down the group.
  4. Boiling point and melting point - Boiling point and melting point increases with increase in atomic number.
  5. Ionization potential - They have high value of ionization potential in their period. It decreases down the group.

Chemical Properties of Halogens

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  1. Reactivity - They are reactive non metals. Their reactivity decreases down the group.
  2. Oxidizing properties - Oxidizing property decreases from fluorine to iodine because the power to accept electron decreases. Thus fluorine is the strongest oxidizing agent in this group and iodine is the weakest.
  3. Reaction with hydrogen - They all form hydride with hydrogen. The reactivity of halogen acids increases from H2F2 to HI. HI is strong reducing agent and the strongest acid.
  4. Reaction with alkali and alkaline earth metals - They form ionic compounds with metals.
  5. Reaction with non metals - They form covalent compounds with non metals.
  6. Reaction with water and acids - Generally halogen compounds do not react with acids or water.

Characteristics of Halogen Family

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The group 7 atoms are found on the right hand side of the periodic table next to noble gases. Halogens can be useful but they may also be dangerous and must be handled with care. This family includes fluorine, chlorine, bromine and iodine.
  1. Fluorine - Fluorine is a vary poisonous and dangerous gas. Fluorine is a diatomic molecule with the formula F2. It has a pale yellow color.
  2. Chlorine - Chlorine is a poisonous gas which should only be used in the fume cupboard. Chlorine is a diatomic molecule with the formula Cl2. It has a pale green color.
  3. Bromine - Bromine (Br2) is a poisonous red liquid. It has a red brown color.
  4. Iodine - Iodine (I2) exist as a dark grey, crystalline solid and as a solid is brittle and crumbly. Solid iodine is a poor electrical and thermal conductor. When warmed, iodine forms a purple vapor.

In general halogen have colored vapors. On going down the group the color of the vapor gets darker.

Uses of Halogens

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  1. Fluorides are added to drinking water and to toothpaste to reduce tooth decay. The halogen chlorine is used to purify water supplies to bleach and to prepare pure hydrochloric acid, along with many other industrial applications.
  2. Bromine is used as ethylene dibromide in antiknock gasoline to remove the lead deposits that form from the other additives, tetra ethyl lead. It is also bromide in many nerve sedatives.
  3. Photography is the oldest industrial used of iodine. it is widely used as an antiseptic in an alcohol solution of iodine called tincture of iodine. Iodine is also used in small amounts to treat goiter condition.