- A Lewis base is a substance that can donate an electron pair to form a covalent bond.

- According to the Lewis theory of acids and bases, a Lewis base is an electron-pair donor.

- They are typically molecules or ions with lone pairs of electrons, which are electrons that are not involved in any chemical bonds.

- Examples of Lewis bases include ammonia (NH3), hydroxide ion (OH-), and pyridine (C5H5N).

Arrhenius base:

- An Arrhenius base is a substance that, when dissolved in water, releases hydroxide ions (OH-) into the solution.

- According to the Arrhenius theory of acids and bases, a base is a substance that increases the concentration of hydroxide ions in a solution.

- Arrhenius bases are typically metal hydroxides, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Key differences:

- The main difference between a Lewis base and an Arrhenius base is that a Lewis base can donate an electron pair, while an Arrhenius base releases hydroxide ions when dissolved in water.

- Lewis bases include a wider variety of substances, such as ammonia and pyridine, while Arrhenius bases are limited to metal hydroxides.

- The concept of a Lewis base is more general and applies to a wider range of chemical reactions, while the concept of an Arrhenius base is more specific to aqueous solutions.