Scandium at a glance
- Atomic number
- 21
- Symbol
- Sc
- Atomic mass
- 44.956 u
- Category
- Transition metal
- Group / period
- 3 / 4
- Electron configuration
- [Ar] 3d 1 4s 2
- State at 25 °C
- Solid
- Melting point
- 1541 °C
- Boiling point
- 2836 °C
- Density
- 2.989 g/cm³
- Electronegativity
- 1.36
- 1st ionization energy
- 633 kJ/mol
- Oxidation states
- +3
- Discovered
- 1879
Atomic structure
A neutral scandium atom has 21 protons and 21 electrons, and its most common isotope carries about 24 neutrons. One atom weighs about 7.47 × 10⁻²⁶ kg, so a mole of scandium (6.022 × 10²³ atoms) weighs 44.956 g. That nucleus holds 1.14 neutrons for every proton. The electrons fill 4 shells (K 2, L 8, M 9, N 2), which gives the configuration [Ar] 3d 1 4s 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, Sc-45. No other element has a stable isotope with mass number 45, so Sc-45 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) scandium is a solid. It melts at 1541 °C and boils at 2836 °C, so it stays liquid across a 1295-degree range. It stays solid in molten iron (1538 °C) but would melt in a welding arc. Its density is 2.989 g/cm³, 2.99 times as dense as water. Its atoms have a radius of about 160 pm (Calcium next door is 180 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.36 on the Pauling scale. Pulling off its outermost electron takes 633 kJ/mol. A bond between scandium and chlorine would be mostly ionic, with an electronegativity difference of 1.8. It releases 18 kJ/mol when it gains an extra electron. Its common oxidation states are +3, so in compounds you will usually meet it as Sc³⁺. Group 3 also holds Yttrium, which shares its outer-shell pattern.
Where it comes from
It makes up 22 mg/kg of Earth's crust, the 31st most abundant element there. It was first identified in 1879, making it the 67th element to be discovered (counting the 11 known since antiquity together).