Copper (Cu)

Copper is the second-best electrical conductor of any metal after silver, and silver is too expensive to wire a house with, so almost all electricity that has ever flowed has flowed through copper. It kills bacteria on contact — a mechanism called contact killing, in which copper ions rupture the cell membrane — so brass door handles in a hospital genuinely stay cleaner than stainless ones. Its configuration is anomalous: [Ar] 4s¹ 3d¹⁰, because a completely filled d subshell is worth borrowing an electron from the 4s shell for.

Properties

Atomic number

29

Symbol

Cu

Standard atomic weight

63.546 u

Category

Transition metal

Group

11

Period

4

Block

d-block

Electron configuration

[Ar] 4s¹ 3d¹⁰

Electrons per shell

2, 8, 18, 1

Melting point

1,357.77 K — 1084.6 °C — 1984.3 °F

Boiling point

2,835 K — 2561.8 °C — 4643.3 °F

Density

8.933 g/cm³

Electronegativity

1.9 (Pauling)

Oxidation states

+2, +1

Discovered

Known since antiquity

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

Noble gas shorthand

[Ar] 4s¹ 3d¹⁰

Shells

K: 2 · L: 8 · M: 18 · N: 1

What it is used for

• Electrical wiring, motor windings and busbars
• Domestic water pipe and heating systems
• Roofing and cladding, where it weathers to green
• Brass and bronze, its two ancient alloys
• Antimicrobial touch surfaces in hospitals

Anomalous electron configuration: [Ar] 4s¹ 3d¹⁰ rather than the predicted 4s² 3d⁹. The green of weathered copper is a carbonate and sulfate patina, not the red-brown oxide, and it protects the metal underneath — the Statue of Liberty's skin is only about 2.4 mm thick.

Neighbours in the table

Group 11

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Copper sits in group 11 with silver, gold, roentgenium.