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Halogen – Elements, Properties and uses

What are halogen atoms ?

Halogen elements are the elements of group VII (column 17) in the periodic table. There are 5 halogens (Fluorine, Chlorine, Bromine, Iodine, and Astatine). The sixth element which is Tennessine atom might have some properties in common with the other elements.

  • Fluorine 9F
  • Chlorine 17Cl
  • Bromine 35Br
  • Iodine 53I
  • Astatine 85At
  • Tennessine 117Ts
Halogen - Elements, Properties and uses


Halogens are all in some way pretty dangerous:

  • Fluorine is a poisonous yellow gas and it is very reactive.
  • Chlorine is a poisonous green gas but it is less reactive.
  • Bromine is a Poisonous brown volatile liquid.
  • Iodine is a dark grey solid that can form poisonous purple vapours, Iodine is also used as an antiseptic.

All of the halogens have 7 electrons on their outer shell so to be stable and acquire the structure of the noble gas, they can exist as pairs of atoms linked together, they share electrons and form a covalent bond with other non-metals such as hydrogen or carbon.

The melting points and boiling points increase as you go down in the group VII, but he reactivity decreases because as you go down the group the outer shell gets away from the positive nucleus, so the attractive force that’s needed to pull in an extra electron from another atom gets weaker and if the halogen can’t attract an electron to complete its outer shell then it can’t react. So the larger atoms at the bottom of the table like Iodine are the least reactive.

The halogen elements can also form ionic bonds with metals. When a halogen gains an electron it forms an ion negatively charged (an anion). The name of these ions is formed by adding the prefix “ide” to the end of the halogen’s name. For example the ion formed by the fluorine is called fluoride.

Halogen name Anion name Anion Chemical formula
Fluorine Fluoride F
ChlorineChloride Cl
BromineBromide Br
IodineIodide I
Name and formula of different anions formed by the halogen elements

Halogens can form ionic compounds with the alkali metals in group 1 like sodium chloride (NaCl).

Finally halogen element can be used in displacement reactions where more reactive halogen is displacing a less reactive one. For example let’s imagine that we pumped some chlorine gas into a solution of Potassium bromide, as the chlorine is more reactive than the bromine because it’s higher up in the group it displaces the bromine to bond to the potassium. The chlorine has taken the bromine’s place to form potassium chloride. The main thing to remember here is just that more reactive halogens will always displace less reactive ones. Fluorine, Chlorine and Bromine could all displace iodine as iodine is the least reactive halogen.

Uses of halogen elements

Halogen atoms are used in many products and processes, from drinking water treatment to refrigeration to computer hard drives. They’re also used in a wide range of military and space applications. But halogens are also important in medical applications, from cancer treatment to organ preservation. Their unique ability to combine with other elements to create compounds with unique properties has led to their wide use as chemical compounds.