Ruthenium (Ru)

Ruthenium is a transition metal with atomic number 44, in period 5 and group 8 of the periodic table. Its atomic mass is 101.07 u and its electron configuration is [Kr] 4d⁷ 5s¹. Solid at 25 °C.

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Key facts

Atomic number	44
Atomic mass	101.07 u
Category	Transition Metal
Period	5
Group	8
Block	d
Electron configuration	[Kr] 4d⁷ 5s¹
Electrons per shell	2, 8, 18, 15, 1
Electronegativity (Pauling)	2.2
Oxidation states	−2, +1, +2, +3, +4, +5, +6, +7, +8common in bold
State at 25 °C	Solid
Melting point	2607 K2333.85 °C
Boiling point	4423 K4149.85 °C
Density	12.1 g/cm³

Atomic properties

First ionization energy	7.36 eV
Electron affinity	101.3 kJ/mol
Atomic radius	134 pm
Covalent radius	146 pm
Van der Waals radius	207 pm
Common ions	Ru³⁺, Ru⁴⁺
Protons, neutrons, electrons	44, 57, 44

Physical and thermal properties

Molar volume	8.17 cm³/mol
Heat of fusion	25.7 kJ/mol
Heat of vaporization	580 kJ/mol
Specific heat	238 J/(kg·K)
Thermal conductivity	120 W/(m·K)
Thermal expansion	6.4 × 10⁻⁶ K⁻¹
Mohs hardness	6.5
Young’s modulus	447 GPa
Crystal structure	Simple hexagonal
Magnetic type	Paramagnetic

Identification and history

CAS number	7440-18-8
Latin name	Ruthenium
Discovered by	Karl Ernst Claus · 1844
Named by	---

Natural isotopes

Isotope	Mass (u)	Abundance
⁹⁶Ru	95.907589	5.54 %
⁹⁸Ru	97.905287	1.87 %
⁹⁹Ru	98.90593	12.76 %
¹⁰⁰Ru	99.90421	12.6 %
¹⁰¹Ru	100.905573	17.06 %
¹⁰²Ru	101.90434	31.55 %
¹⁰⁴Ru	103.905425	18.62 %

Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.

A dash (---) means there is no reliable published measurement. The app never makes one up.

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