Halogens are placed under Group 17 in the periodic table, and the components in this group are Fluorine, Chlorine, Bromine, Iodine, and Astatine. The halogen means salt-former in Greek. Halogens are non-metals that react to reading. You can find them in the earth’s crust and seawater. Halogens are the group of elements in the periodic table and the only one that includes elements that can exist in three states of matter at normal temperature. The term Halogen means salt-producing, because Halogen reacts with many other metals or compounds to produce salts. They are highly reactive and cannot be found as free elements in nature. 

Physical properties of Halogen

The table represents the physical properties of Halogen. 

General physical properties of Halogen

• All the Halogens in group 17 have low boiling and melting points.
• The Halogen molecules are kept intact by the weak forces of Van der Waals forces of attraction, and thus, a tiny amount of heat energy is required to overcome it during boiling or melting. 
• The densities of halogens are considerably low.
• Halogens do not conduct electricity or heat.

The change in the physical properties of Halogen

• The Halogens atomic radius (atomic size) increases as we gradually go down the group. 
• The low melting and boiling points of Halogens increase down the group. 
• The density of Halogens keeps increasing as one moves down the group.

Chemical properties of Halogen

All Halogens in group 17 exhibit similar properties. 

• Reactivity: As we go down the group, the reactivity of Halogens decreases. The reactivity of a Halogen can be known by how effectively its atom accepts one electron to accomplish a stable noble gas electron arrangement (octet electron arrangement). The reactivity is decided depending on how easily a halogen gains one electron.

F + e– → F–

(2,7) (2,8)

Cl + e– → Cl–

(2,8,7) (2,8,8)

Br + e– → Br–

(2,8,18,7) (2,8,18,8)

I + e– → I–

(2,8,18,18,7) (2,8,18,18,8)

• As oxidizing agents: In chemical reactions, oxidizing agents are great electron acceptors. The strength of the Halogen as oxidizing agents diminishes while going down Group 17.

• Electronegativity: Halogens are exceptionally electronegative. The electronegativity of the Halogens decreases down the group.

We see an increase from Fluorine to Astatine in the nuclear size of Halogens. The outer occupied shell (valence)  is screened by more internal shells containing electrons when stretched further away from the nucleus.

This causes a decline in the effective atomic charge-the strength to pull the electrons in a molecule towards its nucleus decreases. Hence, we see a drop in electronegativity from Fluorine to Astatine.

The elements of Group 17 showed comparative chemical properties in their reactions with

• Water delivers two kinds of acids.
• Iron to deliver iron(III) halides.
• Sodium hydroxide solution to produce two types of sodium salts and water.

To foresee the properties of astatine

In the periodic table, the astatine is placed beneath Iodine in Group 17. Hence, Astatine is relied upon to respond with water, iron, and sodium hydroxide solution comparatively to Iodine; however, these reactions are slower (less receptive) than iodine.

For instance:

 At2(s) + H2O(l) HAt(aq) + HOAt(aq)

3At2(s) + 2Fe(s) 2FeAt3 (s)

At3 (s) + 2NaOH(aq) → NaAt(aq) + NaOAt(aq) + H2O(l)

Safeguard in taking care of Group 17 elements

Fluorine isn’t just harmful but also a hazardous reactive gas, while astatine is radioactive. In this way, these two elements are not utilized in school laboratories.

Gasses such as chlorine, bromine and iodine vapor are poisonous and destructive to the respiratory system of any living being.

Therefore, in research centers and laboratories, these glasses should be handled safely with care. The following safeguard measures should be taken while dealing with these Halogens.

• Handle the Halogens in a smoke chamber.
• Wear safety gloves and goggles at all times.

Conclusion

• Halogens are the most reactive since they lie near noble gasses. 
• Halogen can be found on the left of the noble gasses on the periodic table. 
• Halogen forms diatomic molecules in the elemental state, and the bonds are nonpolar covalent single bonds. 
• Halogens combine with other elements to form compounds that show several properties and are never seen uncombined in nature. 
• Fluorine is the most reactive Halogen, and astatine is the least reactive.

We learned about Halogens’ chemical and physical properties and the molecular formulas of different elements in this article.