Why can molecules made of three atoms have a bent or linear shape?

The discussion on bent/linear shape, and its further calculation can be defined as follows:

Linear form molecules containing atoms arranged inside a straight line.Molecules having linear electron-pair geometries have sp hybridization so at central atom.Bend molecular geometry, often called angular or V-shaped, relates to molecules that have a non-collinear organization of 2 adjacent bonds.Bent = Linear however bent given the presence of Lone Pairs; more the Lone Pairs, then higher the bent as well as the smaller its degree. This consists of 3 atoms in total.

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Copper, silver, aluminum, cobalt, chromium, mercury