What type of bond is formed by the attraction between positively charged metal ions and the electrons around them?

A metallic bond is a type of chemical bond formed between positively charged atoms in which the free electrons are shared among a lattice of cations. In contrast, covalent and ionic bonds form between two discrete atoms. Metallic bonding is the main type of chemical bond that forms between metal atoms.

Metallic bonds are seen in pure metals and alloys and some metalloids. For example, graphene (an allotrope of carbon) exhibits two-dimensional metallic bonding. Metals, even pure ones, can form other types of chemical bonds between their atoms. For example, the mercurous ion (Hg22+) can form metal-metal covalent bonds. Pure gallium forms covalent bonds between pairs of atoms that are linked by metallic bonds to surrounding pairs.

The outer energy levels of metal atoms (the s and p orbitals) overlap. At least one of the valence electrons participating in a metallic bond is not shared with a neighbor atom, nor is it lost to form an ion. Instead, the electrons form what may be termed an "electron sea" in which valence electrons are free to move from one atom to another.

The electron sea model is an oversimplification of metallic bonding. Calculations based on electronic band structure or density functions are more accurate. Metallic bonding may be seen as a consequence of a material having many more delocalized energy states than it has delocalized electrons (electron deficiency), so localized unpaired electrons may become delocalized and mobile. The electrons can change energy states and move throughout a lattice in any direction.

Bonding can also take the form of metallic cluster formation, in which delocalized electrons flow around localized cores. Bond formation depends heavily on conditions. For example, hydrogen is a metal under high pressure. As pressure is reduced, bonding changes from metallic to nonpolar covalent.

Because electrons are delocalized around positively charged nuclei, metallic bonding explains many properties of metals.

Electrical conductivity: Most metals are excellent electrical conductors because the electrons in the electron sea are free to move and carry charge. Conductive nonmetals (such as graphite), molten ionic compounds, and aqueous ionic compounds conduct electricity for the same reason—electrons are free to move around.

Thermal conductivity: Metals conduct heat because the free electrons are able to transfer energy away from the heat source and also because vibrations of atoms (phonons) move through a solid metal as a wave.

Ductility: Metals tend to be ductile or able to be drawn into thin wires because local bonds between atoms can be easily broken and also reformed. Single atoms or entire sheets of them can slide past each other and reform bonds.

Malleability: Metals are often malleable or capable of being molded or pounded into a shape, again because bonds between atoms readily break and reform. The binding force between metals is nondirectional, so drawing or shaping a metal is less likely to fracture it. Electrons in a crystal may be replaced by others. Further, because the electrons are free to move away from each other, working a metal doesn't force together like-charged ions, which could fracture a crystal through the strong repulsion.

Metallic luster: Metals tend to be shiny or display metallic luster. They are opaque once a certain minimum thickness is achieved. The electron sea reflects photons off the smooth surface. There is an upper-frequency limit to the light that can be reflected.

The strong attraction between atoms in metallic bonds makes metals strong and gives them high density, high melting point, high boiling point, and low volatility. There are exceptions. For example, mercury is a liquid under ordinary conditions and has a high vapor pressure. In fact, all of the metals in the zinc group (Zn, Cd, and Hg) are relatively volatile.

Because the strength of a bond depends on its participant atoms, it's difficult to rank types of chemical bonds. Covalent, ionic, and metallic bonds may all be strong chemical bonds. Even in molten metal, bonding can be strong. Gallium, for example, is nonvolatile and has a high boiling point even though it has a low melting point. If the conditions are right, metallic bonding doesn't even require a lattice. This has been observed in glasses, which have an amorphous structure.

Jul 9, 2022 | Turito Team

You must have read about metals and other metallic objects. Even you have seen a lot of objects made up of metals. Have you ever wondered what causes different shapes and variations in metallic objects? Why can we make sheets, wire, or any other form of metal? Why do they shine when exposed to light?

What is the connection between one atom of metal and another, and what makes them connected? There are so many fascinating things about metals. But, the reason for most of these causes is metallic bonding.

This article will let you learn about metallic bonding and answer the above questions. Have a look.

 What is Metallic Bonding?

Metallic bonding is the force of attractiveness between valence electrons and metal ions. A chemical bonding arises from the attractive electrostatic force between conduction electrons and positively charged metal ions.

What is metallic bonding? It is described as sharing free electrons among a lattice of positively charged ions (or cations). A metallic bond is an impact that holds the metal ions together in the metallic object. It is a force of attraction between the metallic cations and the delocalised electrons, and this force binds the atoms firmly together in the metallic object.

A metallic bond is electrostatic and only exists in metallic objects. Metallic bonding describes many physical features of metals, such as lustre, flexibility, electrical and thermal conductivity and resistivity, opacity, and strength.

 How is a Metallic Bond Formed?

In the case of the metallic object, the integral particles are fixed metallic cations surrounded by a sea of mobile electrons. These are produced from metallic objects because such objects have low ionisation energy and can easily lose their valence electrons to leave behind positively charged ions (kernels).

These electrons can penetrate easily throughout the metallic lattice, like water in the sea. So, these are called the ‘sea of free electrons.’

Each metallic atom contributes one or more electrons towards this sea of delocalised electrons. These mobile electrons are simultaneously attracted by the positive ions and hold these positive ions together by the electrostatic force of attraction.

The attraction between the kernel and the mobile electrons that hold the kernel together and this force of attraction is known as a metallic bond. The essential particles in metallic crystals are metal atoms held together by a metallic bond.

The following metallic bonding diagram shows the metallic solid-positive ions in a sea of mobile electrons.

Metallic Bond Examples

Generally, all metals are metallic bond examples. But, here are explanations of metallic bonding in some metals, i.e., aluminium, magnesium, and sodium.

The electronic configuration of aluminium (Al) is 1s2 2s2  2p6 3s2 3p1. It has three valence electrons in total. Due to its electropositive nature and delocalised electrons, it can lose these three valence electrons and become Al+3 metallic ions. With such a positive charge, individual Al ions can strongly repel each other. But the sea or cloud of electrons held them together. Due to the greater magnitude of charge and electron density, the melting point of aluminium becomes higher than that of magnesium and sodium.

In the case of magnesium (Mg), electronic configuration 1s2 2s2 2p6 3s2, and sodium (Na), electronic configuration 1s2 2s2 2p6 3s1, the number of valence electrons is 2 and 1, respectively. As a result, their electron density and magnitude of the charge are lower than aluminium. Hence, their melting points are also lower than aluminium.

Therefore, the metallic bonding of aluminium would be stronger than magnesium and sodium. In fact, because of the low number of free electrons, sodium is soft and has a lower melting point than the other two.

 Metallic Bonding Formation Factors

The factors favouring the formation of metallic bonds are:

• The ionisation energy of the metal should be low so that the valence electrons are loosely held by the nucleus and thus become mobile.
• The metals should have high electropositivity, so they do not accept electrons and form anions.
• The vacant orbital should be more than the number of valence electrons so that the mobile electrons can easily move in the vacant orbitals.

 Characteristic Properties of Metallic Bonds

Some important characteristic properties of solids containing metallic bonds are:

Metallic bonding crystals are generally good conductors of electricity. It is because of a sea of free electrons in their structure. Their metallic crystal has mobile or delocalised electrons. When the one end of this crystal comes in contact with an electric field, the mobile electron present there moves towards the positive end of the crystal. When it moves, another electron grasps its position and faces the same situation. In this way, the movement of electrons occurs, leading to the flow of electricity in the crystal. Therefore, solids having metallic bonds are good conductors of electricity.

Like electrical conductivity, metallic crystals are good conductors of heat. It is because when heat is given to one part of the metallic lattice, the delocalised electrons at that end start to absorb the heat energy. After that, these electrons start moving toward the lattice’s cool end. This way, the heat is transferred from one end of the lattice to the other. Hence, it makes them good thermal conductors. The thermal conductivity of metallic objects decreases with an increase in temperature.

They possess lustre and colour in some cases. It is also explained based on mobile electrons present in the metallic lattice. Light collides with the free electrons when it falls on the lattice surface. As a result, these electrons get excited and revert from their original positions. During this movement, they release some energy in the form of light.

They are opaque. It is because when the light falls on metallic objects, the light is absorbed completely by the electronic transition of the sea of electrons. Hence, no light is permitted to pass through them.

They are highly malleable (converted into thin sheets) and ductile (converted into thin wires). When a metallic crystal is beaten, the top layer of positive metal ions move. After that, another layer takes its place. Because of their mobile nature in metallic objects, electrons also move with the positive metallic layer.

Therefore, the position of the positive ions is altered without destroying the structure of the substance, and the freely moving electrons provide a uniform distribution of charges. For this reason, they are easily deformable.

1. High boiling and melting point:

As the position ions are closely packed in the substances containing metallic bonds, most possess high boiling and melting points and have high densities.

Metallic mixtures are called alloys. Metallic objects can form alloys easily. In these alloys, the spherical ions of different atoms share the same sea of electrons.

 Conclusion

Metallic bonding is a chemical bonding that occurs connecting atoms of metallic objects. The chief force holds together the atoms of a metallic crystal. Metallic bonds result from sharing a variable number of electrons with a variable number of atoms. It gives metals their distinctive properties. 

Frequently Asked Questions

 Q1. What are the applications of the metallic bond?

Answer: Metallic bonds hold metal together, but they also generate that sea of electrons that allows electrons to flow. Without this sea of electrons devised by metallic bonds, we couldn’t have all the pleasurable things electricity brings.

 Q2. What are the differences between metallic bonds and ionic bonds?

Answer: The important differences between metallic bonds and ionic bonds are:

Q3. What are the differences between metallic bonds and covalent bonds?

Answer: Differences between metallic bonds and covalent bonds are:

Q4. How is the metallic bond responsible for the higher melting and boiling point of transition metals than alkali metals?

Answer: The strength of the metallic bond depends on the number of valence electrons and the charge on the nucleus. As the number of valence electrons and the charge increases, the strength of the metallic bond increases. Due to this reality, alkali metals are soft and have low melting and boiling points, while transition metals are hard and have high melting and boiling points.