Properties of Metallic Bond

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Properties of Metallic Bond

This lesson aligns with NGSS PS1.A

Introduction

A metallic bond is a distinctive form of chemical bonding characterized by a collective 'cloud' of freely moving valence electrons that are bonded to positively charged ions within a metal. This bonding mechanism can be elucidated as the mutual sharing of free electrons within a lattice composed of positively charged metal ions. The structural arrangement of metallic bonds is quite different to that of ionic and covalent bonds. It is noteworthy that a metal is the only substance that contains a metallic bond. In this article, we will delve into the characteristics of metallic bonding.

Properties of Metallic Bonding

Metallic bonds contribute numerous properties to metals that make them commercially desirable. Some of these properties are briefly described here.

Electron Delocalization:

One of the key characteristics of metallic bonding is the phenomenon of electron delocalization. In this bonding type, the valence electrons are not confined to individual atoms but rather move freely throughout the metal lattice. This creates a unique structure where positive metal ions are held together by a "sea" of mobile electrons.

Electrical Conductivity:

Electrical conductivity quantifies a substance's capacity to facilitate the movement of electric charge. The unrestricted movement of electrons within the electron sea ensures that any electric current applied to the metal effortlessly passes through it.

When a potential difference is introduced to the metal, the delocalized electrons initiate movement towards the positive charge. This is the reason why metals exhibit high electrical conductivity.

Thermal Conductivity:

The thermal conductivity of a material quantifies its capacity to conduct and transfer heat. When heating one end of a metallic substance, the kinetic energy of electrons in that region rises. Through collisions, these electrons transmit their kinetic energies to other electrons within the electron sea.

The greater the mobility of electrons facilitated by metallic bonds, quicker the transfer of kinetic energy. As a result of this unique characteristic of metallic bonds, the delocalized electrons, being highly mobile, effectively convey heat throughout the metallic substance via collisions with other electrons.

Malleability and Ductility:

When an ionic crystal like sodium chloride is beaten with a hammer, it fractures into numerous smaller pieces due to its rigid lattice structure. The atoms in such crystals are held together in a lattice that resists deformation easily. The application of force, as from a hammer, prompts the crystal structure to fracture, leading to the shattering of the entire crystal.

Conversely, in the case of metals, the presence of a sea of electrons within the metallic bond allows for the deformation of the lattice. Consequently, when metals are beaten with a hammer, their rigid lattice structure is deformed rather than fractured. This unique characteristic explains why metals can be hammered into thin sheets. Given their resistance to easy fracture, metals are characterized as highly ductile.

Metallic Luster:

The lustrous or shiny appearance of metals is a consequence of metallic bonding. When light strikes a metallic surface, the photons' energy is absorbed by the sea of electrons forming the metallic bond. This absorption of energy leads to the excitation of electrons, elevating their energy levels. Subsequently, these excited electrons swiftly return to their ground states, releasing light during the de-excitation process. The emission of light resulting from the de-excitation of electrons contributes to the shiny metallic lustre exhibited by the metal.

High Melting and Boiling Points:

Due to the robust nature of metallic bonding, the attractive force between metal atoms is notably strong. Overcoming this force of attraction demands a substantial amount of energy. Consequently, metals generally exhibit high melting and boiling points, with exceptions such as zinc, cadmium, and mercury. The electron configurations of these exceptions, concluding with ns², contribute to their distinctive behavior.

Notably, the strength of the metallic bond persists even when the metal is in a molten state. For instance, gallium, which has a melting point of 29.76°C, demonstrates this phenomenon, as it only boils at a considerably higher temperature of 2400°C. This characteristic molten gallium is a non-volatile liquid.

Summary

Electrical conductivity quantifies a substance's capacity to facilitate the movement of electric charge.
When a potential difference is introduced to the metal, the delocalized electrons initiate movement towards the positive charge. This is the reason why metals exhibit high electrical conductivity.
The thermal conductivity of a material quantifies its capacity to conduct and transfer heat.
The greater the mobility of electrons, facilitated by metallic bonds, quicker the transfer of kinetic energy.
The lustrous or shiny appearance of metals is a consequence of metallic bonding.

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