Rhenium (Re)

Rhenium was the last stable element to be discovered, in 1925, and it is genuinely rare: about one part per billion in the crust, with world production only a few tens of tonnes a year, mostly recovered from the flue dust of molybdenum roasting. It has the third-highest melting point of any element and one of the two highest boiling points — CRC puts it just above tungsten, and which of the pair wins depends on whose measurement you take. Adding around 3-6% to a nickel superalloy lets a jet turbine blade run hotter, which is worth enough fuel that engine makers buy most of the world supply. Rhenium is also the only element with no known biological role that is nevertheless concentrated by a living thing — certain bacteria and some plants take it up.

Properties

Atomic number

75

Symbol

Re

Standard atomic weight

186.21 u

Category

Transition metal

Group

7

Period

6

Block

d-block

Electron configuration

[Xe] 6s² 4f¹⁴ 5d⁵

Electrons per shell

2, 8, 18, 32, 13, 2

Melting point

3,459 K — 3185.8 °C — 5766.5 °F

Boiling point

5,869 K — 5595.9 °C — 10104.5 °F

Density

20.8 g/cm³

Electronegativity

1.9 (Pauling)

Oxidation states

+7, +6, +4

Discovered

1925 by Walter Noddack, Ida Tacke and Otto Berg

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁵

Noble gas shorthand

[Xe] 6s² 4f¹⁴ 5d⁵

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 13 · P: 2

What it is used for

• Single-crystal turbine blades in jet engines — the largest use by far
• Platinum-rhenium catalysts for making high-octane petrol
• Thermocouples for temperatures above 2,000 °C
• X-ray tube targets and filaments

Neighbours in the table

Group 7

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Rhenium sits in group 7 with manganese, technetium, bohrium.