In metallic bonding, the valence electrons of atoms become delocalized or free to move within a "sea" of electrons. This is a unique type of bonding that occurs in metals.
In a metallic bond, the outermost (valence) electrons of metal atoms are not tightly held by any specific atom. Instead, they are able to move freely throughout the entire metal lattice. This is because metal atoms have relatively low ionization energies, meaning it takes relatively little energy to remove an electron from a metal atom.
When metal atoms come together to form a solid, their outermost electrons become shared among all the atoms in the lattice. The positively charged metal ions are arranged in a regular pattern, while the negatively charged delocalized electrons occupy the spaces between the ions.
The delocalized electrons are not associated with any specific atom and are free to move throughout the metal lattice. This mobility gives metals their unique properties, such as high electrical and thermal conductivity. When a voltage is applied to a metal, the delocalized electrons can easily move, carrying the electric current.
In summary, in metallic bonding, the valence electrons of atoms become delocalized and form a "sea" of electrons that are shared among all the metal atoms. This delocalization of electrons allows for the characteristic properties of metals.