Amines (R–NH₂, R₂NH, R₃N) are nitrogen analogs of alcohols and ethers, and their entire personality flows from nitrogen's lone pair. That lone pair makes amines the most important organic bases and good nucleophiles, the two behaviors that dominate their chemistry.

Basicity is the headline property. An amine's lone pair grabs a proton to form an ammonium ion, and the strength of that base is measured by the pKa of its conjugate acid (typically ~9–11 for alkylamines). The factors that tune basicity are a direct application of stability reasoning:

Alkyl groups increase basicity (inductive electron donation stabilizes the positive ammonium ion), so aliphatic amines are more basic than ammonia.
Resonance and hybridization decrease basicity. Aniline (an amine on a benzene ring) is far less basic because its lone pair is delocalized into the aromatic ring and thus less available. Amides are essentially non-basic — the lone pair is tied up in resonance with the carbonyl. Pyridine-type nitrogens (sp² lone pair) are weaker bases than aliphatic amines.

This variable basicity has a hugely useful practical consequence: amines can be extracted and separated by protonating them with acid (converting a water-insoluble amine into a water-soluble ammonium salt) — the basis of the classic acid–base extraction and of why so many drugs are formulated as hydrochloride salts.

Synthesis and reactions worth knowing: reductive amination (a carbonyl + amine → imine → reduced to an amine, the most versatile route), reduction of nitriles or amides with LiAlH₄, and the Gabriel synthesis for clean primary amines. Amines also acylate readily with acid chlorides to form amides (walking down the Track 38 hierarchy) — the reaction that builds peptide bonds.

"Lend the Pair"