The term ‘halogen’ means ‘salt-producing’. Halogens are a group of elements in the periodic table which exhibit similar properties. It is the 17th group (according to IUPAC nomenclature) in the universally known periodic table consisting of all elements known in the world. As of now, five elements are classified as halogens, namely, fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The new artificially created element 117, tennessine (Ts), might also be a halogen.
These elements readily react with alkali metals and alkaline earth metals to produce a wide range of salts like calcium fluoride, silver bromide, potassium iodide, and sodium chloride (common table salt).
All halogen molecules are diatomic.
They can gain an electron by reacting with the atoms of other elements.
Halogens have seven valence electrons. Therefore, they form negative ions that are highly reactive.
Fluorine is one of the most reactive elements to exist.
Halogens have a strong and nasty smell.
Halogens are highly toxic.
They have low melting and boiling points.
They are poor conductors of electricity and heat.
This is the only group in the periodic table group that contains elements in all three states of matter.
Halogen Electron Configuration
The general electronic configuration of halogens is ns2 np5. They always have seven valence electrons. They are one electron less of having a filled outer s and p orbitals. This makes them very reactive.
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Before moving on let us make the concept of electronic configurations clear. The electronic configuration is basically the arrangement of electrons in the orbitals of the atom of an element. The study of electronic configuration helps us in understanding the reactivity of elements and the type of bonds formed by the elements with other elements. It also shows the similarity in the trends of physical and chemical properties of the elements. There are certain principles that we adhere to when writing the electronic configuration of any element.
Pauli’s Exclusion Principle: It is based on quantum numbers. Pauli stated that all four quantum numbers of any two electrons in an atom cannot be identical.
Hund's Rule: Hund's rule of maximum multiplicity states that electrons can get pared up in an orbital only when all the subshells consist of at least one electron in it.
Aufbau Principle: According to this principle, electrons of any element can fill the energy levels in increasing order.
Using these rules the electronic configuration of group 17 elements is ns2 np5, where n is the quantum number of the respective elements.
Let us See the Electronic of Each Element of Halogens Separately
Fluorine (F): It is a pale-yellow diatomic gas at room temperatures, which is highly toxic and corrosive in nature. It has the atomic number 9. It belongs to the 2nd period and is located in the p block. The electron arrangement of fluorine is [He]2s22p6.
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Chlorine (Cl): This is a greenish-yellow coloured gas with a very strong smell. It has atomic number 17 and belongs to p-block, 3rd period. The electronic configuration of this halogen is: [Ne]3s23p5.
Bromine (Br): At room temperature, bromine is a reddish-brown colour liquid with an acidic odour. With atomic number 35, situated in the 4th period and p-block, it has the following electronic configuration: [Ar]3d104s24p5.
Iodine (I): The vapours of iodine gas is violet in colour. It has atomic number 53 and belongs to p-block, 5th period. The electronic configuration is [Kr]4d105s25p5.
Astatine (At): Astatine is an unstable, radioactive compound with an atomic number 85. It belongs to the p-block, 6th period of the periodic table with electronic configuration [Xe]4f145d106s26p5.
The word Halogen comes from the Greek words ‘hals’ meaning salt and ‘gen’ meaning to make.
Fluorine gas is considered to be deadly. Breathing air with fluorine of just 0.1% can cause death. It is considered as one of the most reactive elements in existence.
Small amounts of fluoride are used in water and toothpaste to prevent tooth decay.
Astatine has found uses in medicine although it is radioactive and decays very quickly.
Iodine is used to clean wounds and cuts as it acts as a disinfectant.
The first halogen to be discovered, isolated, and recognized as an element was chlorine. It is also used as a bleaching agent.
Bromine has a very strong and bad odour and gets its name from the Greek word ‘bromos’ meaning stench.