Why does ammonia, nh3, behave as a base when it reacts with an acid? z

The nitrogen atom in ammonia comes with a lone pair of electrons.

Consider the feature of an ammonia molecule:

The central N atom carries a partial positive charge. That N atom would attract protons, which are positive. The molecule can bond to a proton to form an ammonium NH₄⁺ ion. As a result, NH₃ is a Bronsted-Lowry Base.

The central N atom might also share that lone pair of electrons with an electrophile, which is a substance that would readily bond to lone pairs of electrons (typically one that is short of electrons.) H⁺ and BF₃ are examples of electrophiles. Ammonia would react with either readily and share its lone pair of electron. It would thus act as a Lewis base.

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