How do alkali metals react with halogens?

Alkali metals react with halogens to form ionic salts, known as alkali metal halides.

Alkali metals, found in Group 1 of the Periodic Table, are highly reactive due to their single electron in the outermost shell. This electron is easily lost, making alkali metals excellent reducing agents. Halogens, on the other hand, are found in Group 7 of the Periodic Table. They are highly electronegative and have a strong tendency to gain an electron, making them good oxidising agents.

When an alkali metal reacts with a halogen, the metal atom donates its outermost electron to the halogen atom. This results in the formation of a positive metal ion and a negative halogen ion. The oppositely charged ions are then attracted to each other due to electrostatic forces, forming an ionic bond. The resulting compound is an alkali metal halide, which is an ionic salt.

For example, when sodium (an alkali metal) reacts with chlorine (a halogen), sodium chloride (common table salt) is formed. The reaction can be represented as follows: 2Na(s) + Cl2(g) → 2NaCl(s). In this reaction, sodium atoms each lose one electron to become Na+ ions, and chlorine molecules gain these electrons to become Cl- ions. The Na+ and Cl- ions then combine to form sodium chloride.

This reaction is highly exothermic, meaning it releases a large amount of energy in the form of heat and light. This is why alkali metals are stored under oil, to prevent them from reacting with the oxygen and moisture in the air, which could lead to spontaneous combustion.

In summary, the reaction between alkali metals and halogens is a classic example of a redox reaction, where one species is reduced (the halogen) and the other is oxidised (the alkali metal). The product of this reaction is an alkali metal halide, a type of ionic salt.