Gold
Gold is a soft yellow metal that resists corrosion and can be worked into very thin layers. Those qualities make it useful in jewellery, reliable electrical contacts, and the mirrors of a space telescope.
At a glance
- Atomic number
- 79
- Atomic mass
- 196.96657 u
- Phase
- Solid
- Density
- 19.3 g/cm³
- Melting point
- 1,337.33 K
- Boiling point
- 3,109 K
- First ionization energy
- 890.1 kJ/mol
- Electronegativity
- 2.54
- Electron affinity
- 222.747 kJ/mol
- Molar heat capacity
- 25.418 J/(mol·K)
- Period
- 6
- Appearance
- metallic yellow
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Gold’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
54 is the [Xe] core total across five shells.
Preparing the orbital view…
79 protons118 neutrons
Gold-197: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid
At this temperature, gold is a solid.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
AuNeutral atom · no charge
A neutral gold atom. Removing its first electron takes 890 kJ/mol.
Gold’s outer shell holds 1 electron. Electron 2 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 2.2× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- The jump after gold’s outer electrons is small (×2.2), because the electrons in the shell below have similar energies. That’s typical of transition metals, and it’s why many of them, such as iron (Fe²⁺ and Fe³⁺), can form more than one kind of ion.
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 6 | 890 | – | Measured |
| 2 | 5 | 1,949 | 2.2 | Measured |
| 3 | 5 | 2,895 | 1.5 | Calculated |
| 4 | 5 | 4,342 | 1.5 | Calculated |
| 5 | 5 | 5,789 | 1.3 | Calculated |
| 6 | 5 | 7,140 | 1.2 | Calculated |
| 7 | 5 | 9,070 | 1.3 | Calculated |
| 8 | 5 | 10,806 | 1.2 | Calculated |
| 9 | 5 | 12,553 | 1.2 | Calculated |
| 10 | 5 | 14,376 | 1.1 | Calculated |
| 11 | 5 | 16,229 | 1.1 | Estimated |
| 12 | 5 | 23,928 | 1.5 | Estimated |
| 13 | 5 | 26,533 | 1.1 | Calculated |
| 14 | 5 | 28,849 | 1.1 | Calculated |
| 15 | 5 | 31,261 | 1.1 | Calculated |
| 16 | 5 | 35,217 | 1.1 | Calculated |
| 17 | 5 | 37,822 | 1.1 | Calculated |
| 18 | 5 | 41,778 | 1.1 | Calculated |
| 19 | 5 | 46,988 | 1.1 | Calculated |
| 20 | 4 | 50,172 | 1.1 | Calculated |
| 21 | 4 | 53,067 | 1.1 | Calculated |
| 22 | 4 | 57,891 | 1.1 | Calculated |
| 23 | 4 | 62,715 | 1.1 | Calculated |
| 24 | 4 | 68,505 | 1.1 | Calculated |
| 25 | 4 | 73,329 | 1.1 | Calculated |
| 26 | 4 | 79,118 | 1.1 | Calculated |
| 27 | 4 | 83,942 | 1.1 | Calculated |
| 28 | 4 | 89,731 | 1.1 | Calculated |
| 29 | 4 | 95,520 | 1.1 | Calculated |
| 30 | 4 | 100,345 | 1.1 | Calculated |
| 31 | 4 | 106,134 | 1.1 | Calculated |
| 32 | 4 | 110,958 | 1 | Calculated |
| 33 | 4 | 116,747 | 1.1 | Calculated |
| 34 | 4 | 142,316 | 1.2 | Calculated |
| 35 | 4 | 147,333 | 1 | Calculated |
| 36 | 4 | 152,833 | 1 | Calculated |
| 37 | 4 | 158,622 | 1 | Calculated |
| 38 | 4 | 164,218 | 1 | Calculated |
| 39 | 4 | 169,621 | 1 | Calculated |
| 40 | 4 | 178,015 | 1 | Calculated |
| 41 | 4 | 183,708 | 1 | Calculated |
| 42 | 4 | 189,787 | 1 | Calculated |
| 43 | 4 | 195,479 | 1 | Calculated |
| 44 | 4 | 218,153 | 1.1 | Calculated |
| 45 | 4 | 223,846 | 1 | Calculated |
| 46 | 4 | 229,925 | 1 | Calculated |
| 47 | 4 | 235,714 | 1 | Calculated |
| 48 | 4 | 254,721 | 1.1 | Calculated |
| 49 | 4 | 261,282 | 1 | Calculated |
| 50 | 4 | 276,913 | 1.1 | Calculated |
| 51 | 4 | 283,763 | 1 | Estimated |
| 52 | 3 | 471,620 | 1.7 | Measured |
| 53 | 3 | 483,681 | 1 | Calculated |
| 54 | 3 | 497,478 | 1 | Calculated |
| 55 | 3 | 512,048 | 1 | Calculated |
| 56 | 3 | 526,038 | 1 | Calculated |
| 57 | 3 | 539,739 | 1 | Calculated |
| 58 | 3 | 564,053 | 1 | Calculated |
| 59 | 3 | 578,333 | 1 | Calculated |
| 60 | 3 | 593,964 | 1 | Calculated |
| 61 | 3 | 608,340 | 1 | Calculated |
| 62 | 3 | 648,767 | 1.1 | Calculated |
| 63 | 3 | 661,310 | 1 | Calculated |
| 64 | 3 | 675,108 | 1 | Calculated |
| 65 | 3 | 687,940 | 1 | Calculated |
| 66 | 3 | 748,726 | 1.1 | Calculated |
| 67 | 3 | 763,199 | 1 | Calculated |
| 68 | 3 | 792,145 | 1 | Calculated |
| 69 | 3 | 806,617 | 1 | Calculated |
| 70 | 2 | 1,740,595 | 2.2 | Calculated |
| 71 | 2 | 1,775,330 | 1 | Calculated |
| 72 | 2 | 1,812,959 | 1 | Calculated |
| 73 | 2 | 1,847,694 | 1 | Calculated |
| 74 | 2 | 2,071,540 | 1.1 | Calculated |
| 75 | 2 | 2,114,958 | 1 | Calculated |
| 76 | 2 | 2,170,920 | 1 | Calculated |
| 77 | 2 | 2,206,436 | 1 | Calculated |
| 78 | 1 | 8,829,932 | 4 | Calculated |
| 79 | 1 | 8,997,703 | 1 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
Why is gold yellow? Einstein again
Almost every metal is silvery grey: it reflects every colour of light equally. Gold is the exception, and the reason is the same as for mercury next door: Einstein’s relativity. It changes which colours gold swallows and which it bounces back.
Real gold: yellow
- Electron jump
- 5d → 6s needs 2.4 eV (the gap below)
- Absorbs
- Light below about 517 nm: from blue-green down to violet
- Reflects
- Mostly green, yellow, orange and red, so it looks yellow
Relativity pulls gold’s 6s level down and pushes its 5d level up, closing the gap. Now blue light has enough energy to lift electrons across it, so blue is absorbed and the reflected light looks yellow.
- Silver
- Gold
- Gold without relativity
E = mc², at speed
Gold has 79 protons, so its innermost electrons race at over half the speed of light. Einstein’s E = mc² says a resting electron carries 511 keV of energy; the full version, E = γmc², adds a factor γ that grows with speed. Slide through the elements to see how it builds up.
E = mc² at rest = 511 keV
γ = 1 ÷ √(1 − v²/c²) = 1 ÷ √(1 − 0.576²) = 1.224
E = γmc² = 1.224 × 511 keV = 625 keV
γ barely moves at everyday speeds, even at the speed of a rocket. It only takes off as you get close to the speed of light, which is why only heavy atoms, with lots of protons pulling hard, feel it.
Absorption edges from measured optical constants of gold and silver (Johnson and Christy, 1972); gold without relativity from calculations (Pyykkö and Desclaux, 1979), shown here with silver’s edge. Colours come from a simplified reflection model and are approximate. The electron speed and γ are rough estimates from a simple model of the atom.
The conductivity race
Silver is the best conductor of electricity and heat of any element. Copper comes a close second, gold third. So why are the wires in your walls copper, not silver? Race them, then look at the scorecard.
Same wires, same battery: which delivers a fixed amount of charge first?
- Silver100% of silver
- Copper95% of silver
- Gold72% of silver
- Aluminium60% of silver
The clock is slowed down. The gaps between the metals are real, but the winner is given 4 seconds so you can watch. In a real wire the push travels at a large fraction of the speed of light: along a metre of wire it arrives in a few billionths of a second. The electrons themselves crawl: in a household copper wire each one drifts less than a millimetre per second, slower than a snail. The push passes along like a line of marbles, where shoving one end moves the far end at once.
So why copper?
Silver wins the race by only about 5%, but copper is about 800 times more common in the Earth’s crust, so it costs a tiny fraction as much. For long overhead power lines, lightness matters most, so they use aluminium: it conducts less well, but a wire that carries the same current weighs half as much as copper.
| Property | Silver | Copper | Gold | Aluminium |
|---|---|---|---|---|
| Conducts electricity | 100%Best | 95% | 72% | 60% |
| Conducts heat | 100%Best | 93% | 74% | 55% |
| In the Earth’s crust | 0.075 mg per kg | 60 mg per kg | 0.004 mg per kg | 8.2%Best |
| Weight of a wire that conducts as well | 2.3× the lightest | 2.1× the lightest | 6× the lightest | 1× the lightestBest |
| In air | Tarnishes black in air | Slowly turns brown, then green | Never tarnishesBest | Grows a thin, protective skin |
| Mostly used for | Solar cells, switch contacts, top-end electronics | House wiring, motors, circuit boards | Thin plating on connectors that must never corrode | Overhead power lines, where lightness matters |
CRC Handbook of Chemistry and Physics: electrical resistivity at 20 °C, thermal conductivity at 300 K, and abundance in the Earth’s crust. Race times are in proportion to each metal’s conductivity: the best conductor is given 4 seconds. Silver is 1.06 times as conductive as copper. One twist: in a race to warm up the far end of a rod, gold edges past copper, because gold needs less heat to warm up.
How does it compare?
Density
19.3 g/cm³7th highest of 99
Melting point
1,337 K42nd highest of 96
Boiling point
3,243 K33rd highest of 97
Electronegativity
2.5412th highest of 96
First ionization energy
890 kJ/mol23rd highest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
A golden view of the universe
Webb’s primary mirror uses gold-coated beryllium segments. The gold improves their reflection of infrared light.
100 nanometres
The gold coating on each Webb mirror segment is about 100 nanometres thick. The beryllium beneath it supplies the structure; the thin gold surface helps the telescope collect infrared light.
A dependable connection
A contact needs to keep conducting. Gold combines electrical conductivity with resistance to corrosion, making thin coatings useful on electrical connectors. The same softness that allows gold leaf means jewellery often uses harder alloys.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- GoldRoyal Society of Chemistry
- Webb’s mirrorsNASA
- GoldWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database