Halogen Atom

Posted on  by admin
Halogen Atom
Article
Please select which sections you would like to print:

Attaching an electronegative atom to the carbon atom strengthens the halogen⋅⋅⋅halogen contacts. An electrostatic model is proposed based on two assumptions: 1) The presence of a positive electrostatic end cap on the halogen atom (except for fluorine) and 2) the electronic charge is anisotropically distributed around the halogen atom. Halogen - Halogen - Relative reactivity: The great reactivity of fluorine largely stems from the relatively low dissociation energy, a standard measure for bond energies, of the F―F bond (37.7 kilocalories per mole) and its ability to form stable strong bonds with essentially all the other elements. Fluorine (F2) and chlorine (Cl2) are gases at room temperature. Bromine (Br2) is a reddish. Halogens is the group name that is given to fluorine, chlorine, bromine and iodine. Since these elements have very similar behaviour, they are often treated as a group. The term 'halogenation' can thus refer to replacing any number of hydrogen atom with each and any of the members of the group. Loncat ke navigasi Loncat ke pencarian. Halogen adalah kelompok unsur kimia yang berada pada golongan 7 (VII atau VIIA pada sistem lama) di tabel periodik. Kelompok ini terdiri dari fluor (F), klor (Cl), brom (Br), yodium (I), astatin (At), dan tenesin (Ts).

While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.

Our editors will review what you’ve submitted and determine whether to revise the article.

Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!
Articles from Britannica Encyclopedias for elementary and high school students.
Viktor GutmannSee All Contributors
Emeritus Professor of Inorganic Chemistry, Technical University of Vienna. Author of Halogen Chemistry and others.
Alternative Titles: Group 17 element, Group VIIa element, halogen element

Halogen, any of the six nonmetallic elements that constitute Group 17 (Group VIIa) of the periodic table. The halogen elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). They were given the name halogen, from the Greek roots hal- (“salt”) and -gen (“to produce”), because they all produce sodiumsalts of similar properties, of which sodium chloride—table salt, or halite—is best known.

What are halogen elements?

The halogen elements are the six elements in Group 17 of the periodic table. Group 17 is the second column from the right in the periodic table and contains six elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (As), and tennessine (Ts). Astatine and tennessine are radioactive elements with very short half-lives and thus do not occur naturally.

What are the major properties of the halogen elements?

Halogen elements are very reactive. They produce salts with sodium, of which table salt (sodium chloride, NaCl) is the most well-known. The halogen elements have seven valence electrons in their outermost electron shell. Therefore, when these elements can receive an electron from another atom, they form very stable compounds since their outermost shell is full.

What are some uses of halogen elements?

Chlorine is used to purify water. Chlorine also is part of salt, sodium chloride, which is one of the most widely used chemical compounds. Fluorine is used in fluorides, which are added to water supplies to prevent tooth decay. Iodine is used as an antiseptic.

Why are these elements called halogens?

When these elements react with sodium, they produce salts. The most well-known of these is sodium chloride, or common table salt (also called halite). The word halogen comes from the Greek roots hal- meaning “salt” and -gen meaning “to produce.”

Halogen Atom

Because of their great reactivity, the free halogen elements are not found in nature. In combined form, fluorine is the most abundant of the halogens in Earth’s crust. The percentages of the halogens in the igneous rocks of Earth’s crust are 0.06 fluorine, 0.031 chlorine, 0.00016 bromine, and 0.00003 iodine. Astatine and tennessine do not occur in nature, because they consist of only short-lived radioactive isotopes.

The halogen elements show great resemblances to one another in their general chemical behaviour and in the properties of their compounds with other elements. There is, however, a progressive change in properties from fluorine through chlorine, bromine, and iodine to astatine—the difference between two successive elements being most pronounced with fluorine and chlorine. Fluorine is the most reactive of the halogens and, in fact, of all elements, and it has certain other properties that set it apart from the other halogens.

Chlorine is the best known of the halogen elements. The free element is widely used as a water-purification agent, and it is employed in a number of chemical processes. Table salt, sodium chloride, of course, is one of the most familiar chemical compounds. Fluorides are known chiefly for their addition to public water supplies to prevent tooth decay, but organic fluorides are also used as refrigerants and lubricants. Iodine is most familiar as an antiseptic, and bromine is used chiefly to prepare bromine compounds that are used in flame retardants and as general pesticides. In the past ethylene dibromide was extensively used as an additive in leaded gasoline.

Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now

Oxidation

Probably the most important generalization that can be made about the halogen elements is that they are all oxidizing agents; i.e., they raise the oxidation state, or oxidation number, of other elements—a property that used to be equated with combination with oxygen but that is now interpreted in terms of transfer of electrons from one atom to another. In oxidizing another element, a halogen is itself reduced; i.e., the oxidation number 0 of the free element is reduced to −1. The halogens can combine with other elements to form compounds known as halides—namely, fluorides, chlorides, bromides, iodides, and astatides. Many of the halides may be considered to be salts of the respective hydrogen halides, which are colourless gases at room temperature and atmospheric pressure and (except for hydrogen fluoride) form strong acids in aqueous solution. Indeed, the general term salt is derived from rock salt, or table salt (sodium chloride). The tendency of the halogen elements to form saltlike (i.e., highly ionic) compounds increases in the following order: astatine < iodine < bromine < chlorine < fluorine. Fluorides are usually more stable than the corresponding chlorides, bromides, or iodides. (Often astatine is omitted from general discussions of the halogens because less is known about it than about the other elements.)

The oxidizing strength of the halogens increases in the same order—i.e., from astatine to fluorine. Therefore, of the halogen elements, elemental fluorine is prepared with the greatest difficulty and iodine with the least. As a class, the halogen elements are nonmetals, but astatine shows certain properties resembling those of the metals.

Electronic structure

Halogen atom group

The chemical behaviour of the halogen elements can be discussed most conveniently in terms of their position in the periodic table of the elements. In the periodic table the halogens make up Group 17 (according to the numbering system adopted by the International Union of Pure and Applied Chemistry), the group immediately preceding the noble gases. The halogen atoms carry seven valence electrons in their outermost electron shell. These seven outermost electrons are in two different kinds of orbitals, designated s (with two electrons) and p (with five). Potentially, a halogen atom could hold one more electron (in a p orbital), which would give the resulting halide ion the same arrangement (configuration) as that of the noble gas next to it in the periodic table. These electron configurations are exceptionally stable. This pronounced tendency of the halogens to acquire an additional electron renders them strong oxidizers.

At room temperature and atmospheric pressure the halogen elements in their free states exist as diatomic molecules. In molecular fluorine (F2) the atoms are held together by a bond made from the union of a p orbital from each atom, with such a bond being classed as a sigma bond. It should be mentioned that the dissociation energy for fluorine (the energy necessary to break the F―F bond) is over 30 percent smaller than that of chlorine but is similar to that of iodine (I2). The weakness of the F―F single bond compared with chlorine can be ascribed to the small size of fluorine resulting in a decreased overlap of bonding orbitals and an increased repulsion of the nonbonding orbitals. In iodine, however, the p orbitals are more diffuse, which means the bond becomes weaker than in chlorine or bromine.

Quick Facts
key people
related topics

You can see that the atomic radius increases as you go down the Group.

Explaining the increase in atomic radius

The radius of an atom is governed by

  • the number of layers of electrons around the nucleus

  • the pull the outer electrons feel from the nucleus.

Compare fluorine and chlorine:

F2,7
Cl2,8,7

Halogen Atom Pictures

In each case, the outer electrons feel a net pull of 7+ from the nucleus. The positive charge on the nucleus is cut down by the negativeness of the inner electrons.

This is equally true for all the other atoms in Group 7. The outer electrons always feel a net pull of 7+ from the centre.

The only factor which is going to affect the size of the atom is therefore the number of layers of inner electrons which have to be fitted in around the atom. Obviously, the more layers of electrons you have, the more space they will take up - electrons repel each other. That means that the atoms are bound to get bigger as you go down the Group.

Trends in Electronegativity

Halogens On The Periodic Table

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is usually measured on the Pauling scale, on which the most electronegative element (fluorine) is given an electronegativity of 4.0.