Metallic Structures

Metallic bonding is the electrostatic attraction between positively charged metal ions and the surrounding sea of delocalised electrons.
Metals are arranged in a regular, closely-packed pattern known as a lattice structure.

Properties of Metallic Structures

High melting and boiling points: Due to the strength of the metallic bonds, metals typically have high melting and boiling points.
Electrical conductivity: Metals are good conductors of electricity because the delocalised electrons are free to move throughout the structure.
Thermal conductivity: Similarly, metals are good conductors of heat, again due to the mobility of the electrons.
Malleability and Ductility: Metals can be bent or stretched into different shapes without breaking. This is due to the ability of the layers of atoms to slide over each other without disrupting the metallic bonding.
Density: Metals are generally high in density due to the closely-packed lattice structure of their atoms.
Shiny Appearance: Metallic structures have a shiny appearance, known as metallic luster, because of the way delocalised electrons interact with light.

An alloy is a mixture of two or more elements, where at least one element is a metal.
The different-sized atoms of the component elements disrupt the regular arrangement, preventing the layers from sliding over each other easily. This makes alloys harder than the pure metal.
Examples of alloys include brass (copper and zinc) and steel (iron and carbon).