Scandium
[Ar] 3d¹ 4s² · 2 · 8 · 9 · 2
A light transition metal whose existence Mendeleev predicted a decade before it was found, calling it eka-boron. Scandium is rare not because there is little of it, but because it concentrates nowhere.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 21
- Atomic mass
- 44.956 а.е.м.
- Electron configuration
- [Ar] 3d¹ 4s²
- Electrons per shell
- 2 · 8 · 9 · 2
- Block
- d-block
- Group
- Scandium group
- Period
- 4
- Electronegativity (Pauling)
- 1.36
- Electronegativity (Allen)
- 1.19
- Atomic radius
- 184 pm
- Covalent radius
- 170 pm
- Van der Waals radius
- 211 pm
- Ionisation energy 1
- 633.1 kJ/mol
- Ionisation energy 2
- 1 235 kJ/mol
- Ionisation energy 3
- 2 388.6 kJ/mol
- Ionisation energy 4
- 7 090.6 kJ/mol
- Ionisation energy 5
- 8 843 kJ/mol
- Electron affinity
- 18.1 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +1, +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 2.985 g/cm³
- Melting point
- 1 814 K · 1 540.9 °C
- Boiling point
- 3 109 K · 2 835.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 14.1 kJ/mol
- Heat of vaporisation
- 332.7 kJ/mol
- Specific heat capacity
- 0.568 J/(g·K)
- Thermal conductivity
- 15.8 W/(m·K)
Mechanical properties
- Young's modulus
- 74 GPa
- Shear modulus
- 29 GPa
- Bulk modulus
- 57 GPa
- Poisson ratio
- 0.28
- Mohs hardness
- 3
- Brinell hardness
- 750 MPa
Electrical and magnetic properties
- Electrical resistivity
- 562 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 0.05 K
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 330.9 pm · c = 527.3 pm
Abundance
- In the crust
- 22 mg/kg
- In the ocean
- 6·10⁻⁷ mg/L
- In the universe
- 30 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 45Sc | 100 % | stable | — |
Scandium-45 is the only stable isotope. Scandium-46 serves as a radioactive tracer in refining and hydrology.
Discovery
- Year of discovery
- 1879
- Discovered by
- Lars Fredrik Nilson
- Where
- Sweden
- Origin of the name
- from Scandia, the Latin name for Scandinavia
History
Lars Nilson isolated scandium oxide in 1879 from euxenite and gadolinite. Per Cleve quickly recognised it as Mendeleev's predicted eka-boron — one of the earliest confirmations of the periodic law.
Where it occurs
22 mg/kg of the crust, more than lead, but scandium is dispersed and forms almost no minerals of its own. The one that matters, thortveitite, is exceedingly rare.
How it is produced
Almost entirely as a by-product of processing uranium, titanium and nickel ores. World output runs to tens of tonnes a year.
Role in living things
No biological role; present in living organisms only in traces.
Safety
Of low toxicity; occupational poisonings are essentially unrecorded, given how little of it is used.
Uses
- Aluminium–scandium alloys: a fraction of a per cent sharply strengthens a welded joint
- Scandium metal-halide lamps, whose spectrum comes close to daylight
- Solid-oxide fuel cells with scandia-stabilised electrolyte
- High-end bicycle frames, baseball bats and sports equipment
Curiosities
- Scandium is Mendeleev's eka-boron: the predicted atomic mass and properties matched reality to within a few per cent.
- The name is from Scandinavia, where it was discovered.
- A kilogram of scandium costs more than a kilogram of gold, because extracting it is so hard.
- The MiG-29 used aluminium–scandium alloys long before the West knew they existed.