Copper
Copper is a chemical element with symbol Cu (from Latin:cuprum) and atomic number 29. It is a soft, malleable and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a reddish-orange color.
At a glance
- Atomic number
- 29
- Atomic mass
- 63.5463 u
- Phase
- Solid
- Density
- 8.96 g/cm³
- Melting point
- 1,357.77 K
- Boiling point
- 2,835 K
- First ionization energy
- 745.5 kJ/mol
- Electronegativity
- 1.9
- Electron affinity
- 119.235 kJ/mol
- Molar heat capacity
- 24.44 J/(mol·K)
- Period
- 4
- Appearance
- red-orange metallic luster
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Copper’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.
18 is the [Ar] core total across three shells.
Preparing the orbital view…
29 protons34 neutrons
Copper-63: 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, copper 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
CuNeutral atom · no charge
A neutral copper atom. Removing its first electron takes 746 kJ/mol.
Copper’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 2.6× 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 jumps let you count electrons. Between the dashed lines there are 1, then 18, then 8, then 2 bars. Read backwards, that’s 2, 8, 18, 1: the same electrons per shell as the shell model above. Jumps like these are part of the evidence that shells exist.
- 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 | 4 | 746 | – | Measured |
| 2 | 3 | 1,958 | 2.6 | Measured |
| 3 | 3 | 3,555 | 1.8 | Measured |
| 4 | 3 | 5,536 | 1.6 | Estimated |
| 5 | 3 | 7,700 | 1.4 | Estimated |
| 6 | 3 | 9,938 | 1.3 | Estimated |
| 7 | 3 | 13,411 | 1.3 | Estimated |
| 8 | 3 | 16,017 | 1.2 | Calculated |
| 9 | 3 | 19,104 | 1.2 | Calculated |
| 10 | 3 | 22,404 | 1.2 | Estimated |
| 11 | 3 | 25,600 | 1.1 | Measured |
| 12 | 3 | 35,410 | 1.4 | Estimated |
| 13 | 3 | 38,691 | 1.1 | Estimated |
| 14 | 3 | 42,068 | 1.1 | Estimated |
| 15 | 3 | 46,612 | 1.1 | Estimated |
| 16 | 3 | 50,047 | 1.1 | Estimated |
| 17 | 3 | 53,337 | 1.1 | Estimated |
| 18 | 3 | 61,027 | 1.1 | Estimated |
| 19 | 3 | 64,704 | 1.1 | Estimated |
| 20 | 2 | 163,108 | 2.5 | Estimated |
| 21 | 2 | 173,674 | 1.1 | Estimated |
| 22 | 2 | 185,059 | 1.1 | Estimated |
| 23 | 2 | 197,216 | 1.1 | Estimated |
| 24 | 2 | 210,280 | 1.1 | Estimated |
| 25 | 2 | 222,621 | 1.1 | Estimated |
| 26 | 2 | 239,197 | 1.1 | Estimated |
| 27 | 2 | 249,603 | 1 | Calculated |
| 28 | 1 | 1,067,362 | 4.3 | Calculated |
| 29 | 1 | 1,116,106 | 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.
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
8.96 g/cm³33rd highest of 99
Melting point
1,358 K40th highest of 96
Boiling point
2,835 K48th highest of 97
Electronegativity
1.937th highest of 96
First ionization energy
746 kJ/mol39th 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.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- CopperRoyal Society of Chemistry
- CopperWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database