Gold
Atomic Data
| Atomic Number | 79 |
| Symbol | Au |
| Atomic Weight | 196.97 u |
| Density (STP) | 19.3 g/cm³ |
| Melting Point | 1064.18 °C (1337.33 K) |
| Boiling Point | 2855.85 °C (3129 K) |
| Electronegativity | 2.54 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s1 |
| Oxidation States | +1, +3 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 6 / 11 |
| CAS Number | 7440-57-5 |
Electron Configuration
[Xe] 4f14 5d10 6s1
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 1 | 79 |
| Total | 79 | 79 | ||
Isotopes of Gold
Gold is monoisotopic: ¹⁹⁷Au is its only naturally occurring stable isotope, accounting for 100% of all natural Gold.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Gold-197 | ¹⁹⁷Au | 79 | 118 | 100 | Stable |
Abundance & Occurrence
Gold is present in Earth's crust at approximately 0.004 ppm by mass and at approximately 0.6 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Gold compounds: skin sensitisation: Soluble gold salts (sodium aurothiomalate, gold trichloride) can cause allergic contact dermatitis and skin sensitisation; gold jewellery allergy is often attributed to nickel or other alloying metals, but pure gold salts can also sensitise.
- Gold sodium thiomalate (injectable gold): Medical gold therapy for rheumatoid arthritis carries risks of nephrotoxicity, thrombocytopenia, and gold-induced lung disease; these are pharmaceutical risks rather than handling hazards.
- Gold nanoparticles: Gold nanoparticles under investigation for drug delivery and diagnostics may exhibit biological activity not seen with bulk gold; inhalation of nano-scale gold aerosols should be prevented.
- Bulk metal: Bulk gold metal is chemically inert and has extremely low systemic toxicity; it is biocompatible and safe for dental, jewellery, and electronics applications under normal handling conditions.
Gold in the Real World
Real-World Uses
- Electronics and electrical contacts: Gold's resistance to tarnish and oxidation makes it the ideal contact material in edge connectors, IC bond wires, contact pads, and coaxial connector contacts, ensuring reliable low-resistance connections over the lifetime of electronic equipment.
- Jewellery and coinage: Gold's lustrous appearance, corrosion resistance, and cultural value have made it the premier precious metal for jewellery, decorative arts, commemorative coins, and sovereign coins used as investment vehicles for millennia.
- Infrared reflective coatings: Gold reflects over 99% of infrared radiation above ~700 nm; deposited on spacecraft thermal blankets, visor coatings on astronaut helmets, and telescope mirror surfaces, it controls thermal loads in space environments.
- Dental restorations: Gold alloys (type III and IV) are used for dental crowns, inlays, onlays, and bridges because of their biocompatibility, durability, and precise fit; gold remains the standard for posterior load-bearing restorations.
- Medical applications: Gold nanoparticles are under investigation for photothermal cancer treatment and targeted drug delivery; gold salts (auranofin) treat rheumatoid arthritis; gold-198 radioisotope seeds were formerly used in cancer brachytherapy.
- Financial reserves and investment: Central banks hold gold bullion as a reserve asset not dependent on any country's creditworthiness; exchange-traded funds (ETFs) and futures markets provide accessible gold investment for retail and institutional investors.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is gold used for?
Gold's primary uses are in jewellery and investment (coins, bars). In technology, gold is used for electrical contacts in connectors, switches, and printed circuit boards because it does not corrode or tarnish, ensuring reliable low-resistance contacts even after years of use. Gold is used in dentistry for crowns. Gold nanoparticles are used in lateral flow immunoassay tests (including rapid COVID-19 tests) and are under development as targeted drug delivery vehicles.
Why doesn't gold tarnish?
Gold is chemically inert because it has a very high electronegativity for a metal and a filled 5d electron shell that makes it unwilling to donate electrons to react with oxygen, water, or common acids. Gold sits at the far right of the electromotive series: it can only be dissolved by oxidising acids combined with complexing agents, most notably aqua regia (a mixture of nitric and hydrochloric acids) or cyanide solutions.
How was gold discovered?
Gold is one of the oldest metals known to humanity. It occurs naturally as a free metal in rivers and rock veins, and its brilliant colour and resistance to tarnish made it immediately attractive. Gold artefacts date back at least 6,000 years to ancient Egypt and Mesopotamia. Gold nuggets can be collected without any metallurgical processing, which is why it was one of the very first metals used by humans.
Why is gold so dense?
Gold's high density (19.3 g/cm3) results from two factors: its large atomic mass (197 amu) and relativistic effects. At gold's high atomic number, the core electrons travel at a significant fraction of the speed of light, causing them to behave as if they are heavier (a relativistic mass effect). This makes the 6s electrons contract toward the nucleus, pulling the outer electrons inward and increasing the density. Relativity also explains gold's yellow colour and the weakness of its tendency to react.