The electron density between these bonds is such that the electrons are delocalized and form a “sea” where they move freely. It can also be expressed by quantum mechanics: some electrons (there are usually one to seven per atom) are arranged in orbitals with multiple centers that stretch across the metal surface.
Likewise, electrons retain a certain location in the metal, although the probability distribution of the electron cloud has a higher density around some specific atoms. This is due to the fact that when a certain current is applied, they manifest their conductivity in a specific direction.
Fundamentals of the electron sea theory
Metallic elements have a great tendency to donate electrons from their last energy level (valence shell), due to their low ionization energy in relation to other elements.
As a metal has a large number of atoms that are linked together, it can be assumed that said metal forms a group of metal cations that are submerged in a kind of sea of valence electrons that have a great delocalization.
Considering that the electrostatic attractive forces that exist between the cation (positive charge) and the electron (negative charge) have the metal atoms strongly bonded, he imagines the delocalization of the valence electrons behaving like an electrostatic adhesive that keeps them bound to metal cations.
In this way, it can be inferred that the greater the number of electrons present in the valence layer of a metal, this kind of electrostatic adhesive will have a greater strength.
The theory of the sea of electrons offers a simple explanation to the characteristics of metallic species such as resistance, conductivity, ductility and malleability, which vary from one metal to another.
It has been discovered that the resistance conferred on metals is due to the great delocalization that their electrons present, which generates a very high cohesion force between the atoms that form them.
In this way, ductility is known as the ability of certain materials to allow the deformation of their structure, without yielding enough to break, when they are subjected to certain forces.
Both the ductility and the malleability of a metal are determined by the fact that the valence electrons are delocalized in all directions in the form of layers, which causes them to move on top of each other under the action of an external force, avoiding the breakage of the metal structure but allowing its deformation.
Likewise, the freedom of movement of the delocalized electrons allows there to be a flow of electric current, making the metals have very good conductivity of electricity.
In addition, this phenomenon of free movement of the electrons allows the transfer of kinetic energy between the different regions of the metal, which promotes the transmission of heat and makes the metals manifest a great thermal conductivity.
Theory of the sea of electrons in metallic crystals
Crystals are solid substances that have physical and chemical properties — such as density, melting point, and hardness — that are established by the kind of forces that make the particles that make them hold together.
In a way, metallic-type crystals are considered to have the simplest structures, because each “point” of the crystal lattice has been occupied by an atom of the metal itself.
In this same sense, it has been determined that generally the structure of metal crystals is cubic and is centered on the faces or on the body.
However, these species can also have a hexagonal shape and have a fairly compact packing, which gives them that enormous density that is characteristic of them.
Due to this structural reason, the bonds that form in metallic crystals are different from those that occur in other classes of crystals. Electrons that can form bonds are delocalized throughout the crystal structure, as explained above.
Disadvantages of the theory
In metallic atoms there is a small amount of valence electrons in proportion to their energy levels; that is, there are a greater number of energy states available than the number of bonded electrons.
This implies that, as there is a strong electronic delocalization and also energetic bands that have been partially filled, the electrons can move through the reticular structure when they are subjected to an electric field coming from the outside, in addition to forming the ocean of electrons that supports network permeability.
So the union of metals is interpreted as a conglomerate of positively charged ions coupled by a sea of electrons (negatively charged).
However, there are characteristics that are not explained by this model, such as the formation of certain alloys between metals with specific compositions or the stability of collective metallic bonds, among others.
These drawbacks are explained by quantum mechanics, because both this theory and many other approximations have been established based on the simplest model of a single electron, while trying to apply it in much more complex structures of multielectronic atoms.