Ruthenium at a glance
- Atomic number
- 44
- Symbol
- Ru
- Atomic mass
- 101.07 u
- Category
- Transition metal
- Group / period
- 8 / 5
- Electron configuration
- [Kr] 4d 7 5s 1
- State at 25 °C
- Solid
- Melting point
- 2334 °C
- Boiling point
- 4150 °C
- Density
- 12.37 g/cm³
- Electronegativity
- 2.2
- 1st ionization energy
- 710 kJ/mol
- Oxidation states
- +3, +4
- Discovered
- 1844
Atomic structure
A neutral ruthenium atom has 44 protons and 44 electrons, and its most common isotope carries about 57 neutrons. One atom weighs about 1.68 × 10⁻²⁵ kg, so a mole of ruthenium (6.022 × 10²³ atoms) weighs 101.07 g. That nucleus holds 1.3 neutrons for every proton. The electrons fill 5 shells (K 2, L 8, M 18, N 15, O 1), which gives the configuration [Kr] 4d 7 5s 1. 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. Its configuration breaks the simple filling order: one electron moves so that a subshell becomes half-full or full, which is more stable. It has 7 stable isotopes: Ru-96, Ru-98, Ru-99, Ru-100, Ru-101, Ru-102 and Ru-104. No other element has a stable isotope with mass number 101, so Ru-101 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) ruthenium is a solid. It melts at 2334 °C and boils at 4150 °C, so it stays liquid across a 1816-degree range. It stays solid in molten iron (1538 °C) but would melt in a welding arc. That is the 9th highest melting point of any element. Its density is 12.37 g/cm³, 12.4 times as dense as water. Its atoms have a radius of about 130 pm (Technetium next door is 135 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 2.2 on the Pauling scale. Pulling off its outermost electron takes 710 kJ/mol, less than Iron above it (763 kJ/mol). A bond between ruthenium and chlorine would be polar covalent, with an electronegativity difference of 0.96. It releases 101 kJ/mol when it gains an extra electron. Its common oxidation states are +3, +4, so in compounds you will usually meet it as Ru³⁺ and Ru⁴⁺. Group 8 also holds Iron, Osmium and Hassium, which share its outer-shell pattern.
Where it comes from
It makes up 0.001 mg/kg of Earth's crust, the 77th most abundant element there. It was first identified in 1844, making it the 58th element to be discovered (counting the 11 known since antiquity together).