Group 7 - The Halogens

Group 7 - The Halogens

General Properties

  • The elements in Group 7 of the Periodic Table are called the Halogens. They include fluorine, chlorine, bromine, iodine and astatine.
  • Halogens are non-metals and consist of diatomic molecules (two atoms per molecule).
  • They have seven electrons in their outermost shell, which makes them highly reactive as they tend to gain one electron to achieve a full outer shell.
  • The reactivity of Halogens decreases down the group. Fluorine is the most reactive halogen, and astatine is the least.
  • This can be explained by the increase in atomic radius and shielding effect down the group, thus the attraction of the nucleus for an added electron decreases.
  • There is an increase in melting and boiling points down the group, due to an increase in the number of electrons leading to stronger van der Waals forces.

Occurrence and Extraction

  • Fluorine and chlorine are found in nature in their ionic forms, as fluorides and chlorides.
  • In sea water, chlorine is present as chloride ions (Cl⁻).
  • Metallic sodium and chlorine gas can be produced from brine (solution of sodium chloride in water) through electrolysis.
  • The other halogens (bromine, iodine) occur in only trace amounts in sea water.

The Chlor-alkali Industry

  • One of the most important industrial applications of chlorine is in the chlor-alkali industry, which produces chlorine, hydrogen, and sodium hydroxide.
  • This is achieved through the electrolysis of brine, which produces chlorine gas at the anode and hydrogen gas at the cathode.
  • Chlorine can be used to manufacture bleach and plastics, while sodium hydroxide is used in soap production.

Remember, a good understanding of the properties and trends within Group 7, and the ability to explain these trends, are fundamental in mastering this topic.