Metals are a large group of elements, making up the majority of the periodic table, which share a defining set of physical and chemical properties. Chemically, metals are characterized by their tendency to readily lose their outermost electrons, forming positively charged ions (cations). This behavior makes them electropositive, setting them apart from nonmetals. The universal characteristics that define this extensive group of elements stem from their unique internal atomic structure and the way their atoms bond together.
Exceptional Conductivity (Electrical and Thermal)
One of the most recognized properties of metals is their superior ability to conduct both electricity and heat efficiently. When a voltage is applied, the numerous free-moving electrons within the structure flow rapidly, creating an electric current with very little resistance. This is why metals like copper are the standard material for electrical wiring.
Metals are similarly proficient at transferring heat, a property called thermal conductivity. When a section of metal is heated, the mobile electrons gain kinetic energy and quickly spread the thermal energy throughout the entire structure by colliding with nearby atoms. The fact that the same free electrons are responsible for both types of transport explains the strong correlation between a metal’s electrical and thermal conductivity.
Structural Flexibility (Malleability and Ductility)
Metals possess mechanical properties that allow them to be shaped and reformed without fracturing, a feature known as plastic deformation. Malleability refers to the ability of a metal to be permanently deformed under compressive stress, such as being hammered or pressed into thin sheets. Aluminum foil demonstrates this property, having been rolled into an extremely thin sheet.
The related property of ductility describes a metal’s capacity to be stretched or drawn into a thin wire under tensile stress without breaking. Copper is highly valued for its ductility, allowing it to be manufactured into the fine wires used in electronics. Both malleability and ductility are possible because the regular layers of atoms within the metal lattice can slide past one another when a force is applied.
Defining Physical Characteristics (Luster, Density, and State)
Beyond their conductive and mechanical properties, metals share several distinct physical characteristics. Metals exhibit a characteristic shiny appearance, known as metallic luster, when their surface is polished or freshly exposed. This reflective quality is caused by the free electrons on the surface absorbing and immediately re-emitting light across the visible spectrum.
Most metals are notably dense, packing a high amount of mass into a small volume. This high density results from the atoms being closely packed together in an organized crystal lattice structure. Furthermore, almost all metals are solid at standard room temperature and pressure, with the notable exception of mercury, which exists as a liquid.
The Role of Metallic Bonding
The underlying cause for all these common properties is the unique type of chemical attraction known as metallic bonding. This bond forms when the outermost valence electrons detach from individual metal atoms and become delocalized, meaning they are not fixed to any single atom. The result is a lattice of positively charged metal ions surrounded by a mobile “sea” of these free-flowing electrons.
This electron sea model provides the mechanism for the observed properties of metals. The free movement of the delocalized electrons allows for the rapid transport of electrical charge and heat energy, explaining the high conductivity. When a force is applied, the positive ions are able to slide past each other without creating repulsive forces, enabling the malleability and ductility of the metal.