Most metals are ductile and malleable because of their unique atomic structure and metallic bonding. Metals consist of a lattice of positive ions surrounded by a "sea" of delocalized electrons, allowing layers of metal ions to slide over each other when force is applied without breaking the metallic bond. This sliding ability enables metals to deform plastically—being stretched into wires (ductility) or hammered into sheets (malleability)—without fracturing, unlike covalent or ionic bonds, which are rigid and brittle. The delocalized electrons adjust their positions to maintain the attraction between ions, facilitating this flexibility in shape.
Additionally, the crystal structure symmetry and density, as well as the grain size of the metal, influence these properties. Dense, symmetrical crystal structures and large grains tend to enhance malleability and ductility, while smaller grain sizes can increase strength and ductility by hindering dislocation movement.
In brief, the combination of metallic bonding, lattice structure, and electron mobility makes most metals capable of being ductile and malleable.