Rhenium at a glance
- Atomic number
- 75
- Symbol
- Re
- Atomic mass
- 186.21 u
- Category
- Transition metal
- Group / period
- 7 / 6
- Electron configuration
- [Xe] 4f 14 5d 5 6s 2
- State at 25 °C
- Solid
- Melting point
- 3186 °C
- Boiling point
- 5596 °C
- Density
- 21.02 g/cm³
- Electronegativity
- 1.9
- 1st ionization energy
- 760 kJ/mol
- Oxidation states
- +7, +4
- Discovered
- 1925
Atomic structure
A neutral rhenium atom has 75 protons and 75 electrons, and its most common isotope carries about 111 neutrons. One atom weighs about 3.09 × 10⁻²⁵ kg, so a mole of rhenium (6.022 × 10²³ atoms) weighs 186.21 g. That nucleus holds 1.48 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 6 shells (K 2, L 8, M 18, N 32, O 13, P 2), which gives the configuration [Xe] 4f 14 5d 5 6s 2. As a d-block element, both its outer s electrons and its inner d electrons can take part in bonding, which is why it shows more than one oxidation state. It has only one stable isotope, Re-185, plus the long-lived Re-187. Its most common isotope, Re-186, has the same mass number as W-186: isobars, nuclei of different elements with 186 nucleons each.
Physical properties
At room temperature (25 °C) rhenium is a solid. It melts at 3186 °C and boils at 5596 °C, so it stays liquid across a 2410-degree range. It stays solid in a welding arc but would melt in the surface of the Sun. That is the 3rd highest melting point of any element. Its density is 21.02 g/cm³, 21 times as dense as water. Its atoms have a radius of about 135 pm (Tungsten next door is 135 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.9 on the Pauling scale. Pulling off its outermost electron takes 760 kJ/mol, more than Technetium above it (702 kJ/mol). A bond between rhenium and chlorine would be polar covalent, with an electronegativity difference of 1.3. It releases 6 kJ/mol when it gains an extra electron. Its common oxidation states are +7, +4, so in compounds you will usually meet it as Re⁷⁺ and Re⁴⁺. Group 7 also holds Manganese, Technetium and Bohrium, which share its outer-shell pattern.
Where it comes from
It makes up 0.0007 mg/kg of Earth's crust, the 81st most abundant element there. It was first identified in 1925, making it the 88th element to be discovered (counting the 11 known since antiquity together).