Gold
Au
Description
Gold (Au) is a dense, soft, and remarkably stable transition metal characterized by its iconic bright yellow luster. As a "noble metal," it is one of the least reactive chemical elements and is typically found in its native, elemental form in nature. Beyond its historical status as a symbol of wealth, gold's unique physical and electronic properties make it a critical material in advanced technology and high-precision engineering.
Crystallographic Structure
In the context of solid-state physics and structural modeling, gold is a quintessential example of the Face-Centered Cubic (FCC) lattice system. This high-symmetry arrangement is responsible for the metal's extraordinary ability to deform without fracturing.
- Crystal System: Cubic (FCC)
- Lattice Parameter: a = 4.078 Å at room temperature.
- Coordination Number: 12
- Atomic Packing Factor (APF): 0.74
- Interatomic Distance: $\approx 2.88$ Å
- Symmetry Class: $Fm\bar{3}m$ (Space group 225)
Properties
Atomic & Physical Properties
Gold is uniquely defined by its extreme density and unparalleled ductility. It is so malleable that a single gram can be beaten into a sheet covering nearly one square meter (gold leaf), or drawn into a wire miles long.
- Atomic Number: 79
- Atomic Mass: 196.967 u
- Melting Point: 1,064.18°C
- Boiling Point: 2,856°C
- Density: $19.30\text{ g/cm}^3$ (Nearly twice as dense as lead)
- Specific Heat Capacity: $0.129\text{ J/g}\cdot\text{K}$
Applications
- Electronics & Computing: Essential for high-end connectors, bond wires in microchips, and smartphone components where reliable signal transmission is mandatory.
- Aerospace Technology: Used in the visors of astronaut helmets and as a coating on satellites and the James Webb Space Telescope to reflect heat and protect against solar radiation.
- Jewelry & Investment: Accounts for the largest global consumption of gold, prized for its aesthetic brilliance, rarity, and hedge against inflation.
- Nanotechnology & Medicine: Gold nanoparticles are used in rapid diagnostic tests (like pregnancy tests) and are being researched for targeted cancer therapies and drug delivery systems.
- Glass Manufacturing: Small amounts of gold are sometimes annealed into glass to reflect solar heat outward in the summer and retain internal heat during winter.
Unit Cell Axes
a=4.078 b=4.078 c=4.078
Unit Cell Angles
α=90° β=90° γ=90°
Lattice Type
fcc
Grid Expansion
Appearance
Coordination