Metal Bonds

Electrical Conductivity
Electrical conductivity is a measure of the ability of a substance to allow a charge to move through it. Since the movement of electrons is not restricted in the electron sea, any electric current passed through the metal passes through it, as illustrated below.
When a potential difference is introduced to the metal, the delocalized electrons start moving towards the positive charge. This is the reason why metals are generally good conductors of electric current.

Thermal Conductivity
The thermal conductivity of a material is a measure of its ability to conduct/transfer heat. When one end of a metallic substance is heated, the kinetic energy of the electrons in that area increases. These electrons transfer their kinetic energies to other electrons in the sea via collisions.
The greater the mobility of the electrons, the quicker the transfer of kinetic energy. Due to metallic bonds, the delocalized electrons are highly mobile, and they transfer the heat through the metallic substance by colliding with other electrons.

Malleability and Ductility
When an ionic crystal (such as sodium chloride crystal) is beaten with a hammer, it shatters into many smaller pieces. This is because the atoms in the crystals are held together in a rigid lattice that is not easily deformed. The introduction of a force (from the hammer) causes the crystal structure to fracture, resulting in the shattering of the crystal.
In the case of metals, the sea of electrons in the metallic bond enables the deformation of the lattice. Therefore, when metals are beaten with a hammer, the rigid lattice is deformed and not fractured. This is why metals can be beaten into thin sheets. Since these lattices do not fracture easily, metals are said to be highly ductile.

Metallic Luster
When light is incident on a metallic surface, the energy of the photon is absorbed by the sea of electrons that constitute the metallic bond. The absorption of energy excites the electrons, increasing their energy levels. These excited electrons quickly return to their ground states, emitting light in the process. This emission of light due to the de-excitation of electrons attributes a shiny metallic lustre to the metal.

High Melting and Boiling Points
As a result of powerful metallic bonding, the attractive force between the metal atoms is quite strong. In order to overcome this force of attraction, a great deal of energy is required. This is the reason why metals tend to have high melting and boiling points. The exceptions to this include zinc, cadmium, and mercury (explained by their electron configurations, which end with ns2).
The metallic bond can retain its strength even when the metal is in its melt state. For example, gallium melts at 29.76oC but boils only at 2400oC. Therefore, molten gallium is a non volatile liquid.

To describe Metal Bonds formation, the concept of a sea or cloud of electrons has been used to help visualize the delocalization of the electrons. Valence electrons of metals are only loosely bonded to their nuclei because they are shielded by the more inner energy levels of electrons. In other words, valence electrons in a Metal Bonds can be associated with any atom within the metal sample. This, along with the closely packed and patterned lattice-like arrangement of the atoms, allows the valence electrons to roam free from a particular parent atom and it's corresponding nucleus. This sea or cloud of electrons have a negative collective charge and are electrically attracted to the positively charged nuclei and form an omnipresent or blanket of cohesion.

The existence of Metal Bonds is an important factor that gives metals their special and unique properties. Metals behave in certain ways and have a typical appearance that help us recognize such a material as a metal and help us describe metallic bonding. Some of the characteristics of Metal Bonds include strength, malleability, ductility, thermal and electrical conductivity, opacity and luster. These characteristics are key observations to help describe metallic bonding.

Strength
The strength of a metallic bond depends on the electron configuration of the metal atom. This was seen with the metallic bond example described above. The number of valence electrons and the orbital energy levels of those valence electrons determine the delocalization of the electrons and ultimately the strength of the metallic bond. More valence electrons would create a greater metallic bond strength. The greater the positive charge of the positive ion created, the stronger the strength of the metallic bond. As the distance decreases between the cations or positive ions of the metal atoms that have lost their valence electrons, the greater the strength of the metallic bond.

Malleability
As described above, because of Metal Bonds the atoms of metals are arranged in a crystal-like lattice. Unlike a typical crystal, which will break and shatter when receiving a large force upon it, a metal can deform its shape while still staying intact because of the ubiquitous sea or cloud of electrons that surround all of the nuclei of the atoms. This characteristic allows metals to be shaped, pressed and formed into sheets or other useful forms.

Metal Bonds are important to the properties of metals. The delocalization of electrons gives rise to the electrical conductivity of metal materials. This also allows for good heat conductivity and movement of heat through the metallic substances. Since electrons are able to move freely, they can easily transfer energy and electricity through the metal. Metals are ductile and malleable, meaning they can be shaped, bent, and formed into wires. This is due to metal atoms being able to break and reform Metal Bonds with neighboring atoms. The electrons flow easily, allowing metallic bond breakage and formation when the metal is manipulated. This does not mean that the Metal Bonds are weak. Metal atoms form strong interactions with each other, giving rise to high melting and boiling points. Lastly, Metal Bonds give rise to the characteristic shine of metals. The "soup" of electrons that metal atoms are dispersed in, reflects photons. This gives metals their luster or shine.

The energy band theory of metallic bonding utilizes a quantum mechanical viewpoint to account for the formation of metallic bonds. Therefore, the energy band theory, also known as the quantum mechanical model of metallic bonding, has five basic ideas:
● In order to make the few valence electrons (1, 2 or 3) of metal atoms can adapt to the needs of the high coordination number, bonding valence electrons must be "out of the domain" (i.e., no longer subordinate to any particular atom), all the valence electrons should belong to the entire metal lattice of atoms in common.
● The metal lattice in the atom is very dense, can form many molecular orbitals, and neighboring molecular orbitals energy difference is very small, can be considered between the energy levels of energy change is basically continuous.
● The molecular orbitals formed by the energy band, can also be seen as a close stack of metal atoms of the electronic energy levels occurring in the overlap, this energy band belongs to the entire metal crystal. For example, lithium metal lithium atoms in the 1S energy levels overlap each other to form a metal lattice in the 1S energy band, and so on. Each energy band can include many similar energy levels, and thus each energy band will include a fairly large energy range, sometimes up to 418 kJ/mol.
● According to the different atomic orbital energy levels, metal crystals can have different energy bands (such as lithium metal in the 1s and 2s energy bands), formed by the atomic orbitals have been filled with electrons of the energy level of the low-energy energy bands, called the "full band"; by the atomic orbitals are not filled with electrons of the energy level of the formation of high-energy energy bands, called the The high energy bands formed by the energy levels of the atomic orbitals not filled with electrons are called "conduction bands". The energy difference between these two types of energy bands is very large, so that the low energy band in the electron to the high energy band jump is almost impossible, so the energy interval between these two types of energy levels is called "forbidden band". For example, the metal lithium (electron layer structure for 1s22s1) 1s orbital has been filled with electrons, 2s orbital is not full of electrons, 1s energy band is a full band, 2s energy band is a conduction band, the energy difference between the two is relatively disparate, the interval between them is a forbidden band, is the electron can not be overstepped (i.e., electrons can not be from the 1s band jump to the 2s energy band). But 2S energy band in the electron can be in the case of accepting external energy, in the band neighboring energy levels in the free movement.
● The neighboring energy bands in the metal can also overlap each other, such as beryllium (electron layer structure of 1s22s2) 2s orbitals have been filled with electrons, 2s energy band should be a full band, it seems that beryllium should be a nonconductor. But because of beryllium's 2s energy band and empty 2p energy band energy is very close and can overlap, 2s energy band electrons can be upgraded into the 2p energy band movement, so beryllium is still a good conductivity of the metal, and has the generality of the metal.

When an applied electric field is applied to a metal, electrons in the conduction band jump to higher energy levels in the energy band and move through the lattice in the direction of the applied electric field, which explains the electrical conductivity of metals. Electrons in the energy bands can absorb light energy and also emit the absorbed energy back out, which explains the luster of metals and the fact that metals are excellent reflectors of radiant energy. Electrons can also transmit thermal energy, indicating that metals are thermally conductive. Apply stress to metal crystals, because the electrons in the metal is out of domain (i.e., does not belong to any of the atoms and belong to the metal as a whole), a place where the metal bond is broken, in another place and can form a metal bond, so the mechanical processing will not destroy the structure of the metal, but only to change the shape of the metal, which is the reason why the metal has a common mechanical processing properties such as ductility, spreading, plasticity, and so on. The more unpaired valence electrons the metal atoms provide for the formation of energy bands, the stronger the metallic bond, the higher the melting and boiling points, and the higher the density and hardness in response to the physical properties.

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