Most of the physical properties that we associate with metals can be explained in terms of this model of closely packed positive ions held together by delocalized electrons.

When pressure is applied to a metal, the positive ions can roll past one another with little opposition, like marbles in mineral oil. The delocalized electrons "lubricate" this flow by shielding each positive ion from the charge of its neighbors. Layers of atoms can be bent, pushed out of shape, or pulled into a thin column without breaking the attraction between atoms.

Hence metals are flexible, malleable (capable of being hammered into new shapes), and ductile (capable of being drawn into wires). If a foreign object such as a knife blade is intruded between layers of atoms in a soft metal like copper, the bonding of metal atoms on either side of the knife cut is unimpaired.

In view of the role that electrons play in holding metals together, perhaps a better image of metal structure than marbles in mineral oil would be marbles in molasses.

Positive ions in a metal can be pushed past one another without flying apart because they are held together by a "sea" of negative electrons.