Chemical element · reference page

21Sc

Scandium

Scandium is element 21 (Sc), located in period 4, group 3 and the d block. At room temperature its reference phase is solid. Its electron configuration is [Ar] 3d1 4s2.

Atomic number21

Standard atomic weight44.955907(4)

Group3

Period4

Blockd

Electron configuration[Ar] 3d1 4s2

Electronic structure

What controls its chemistry

The d subshell participates in the chemistry of scandium. Transition metals can use electrons of similar energies in bonding, which is why variable oxidation states, coordination compounds and catalytic behaviour are common across the d block.

Its electron configuration, [Ar] 3d1 4s2, should be read together with the oxidation state of the compound: removing electrons changes which d orbitals are occupied and can alter colour, magnetism, bonding and reactivity.

Chemical forms

Compounds, ions and materials

For scandium, important chemical forms include metals and alloys, oxides, halides and coordination compounds. Variable oxidation states are common because s and d electrons have similar energies, and ligands around the metal ion can strongly alter colour, magnetism and reactivity.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 2.985 g/cm³. The melting point is 1 814 K (1 541 °C). The boiling point is 3 109 K (2 836 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where scandium is found and used

In practice, scandium is encountered in alloys, lighting and scientific research.

In practice

Examples of real uses

Alloys

Scandium is added to metals to change strength, corrosion resistance, melting behaviour or high-temperature performance.

Lighting

Scandium is used because atoms or compounds of this element interact with light in a useful and reproducible way.

Scientific research

Scandium is produced, isolated or measured mainly to test atomic, nuclear and periodic trends rather than for bulk commercial use.

Periodic position

What its neighbours tell us

Scandium is in period 4 and group 3. In the neighbourhood shown here, it lies between calcium and titanium in the same period; yttrium is directly below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationtransition metal

Phase at room temperatureSolid

Electron shells2 · 8 · 9 · 2

Density2.985 g/cm³

Melting point1 814 K (1 541 °C)

Boiling point3 109 K (2 836 °C)

Pauling electronegativity1.36

First ionisation energy633.1 kJ/mol

Electron affinity18 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of scandium is associated with Lars Fredrik Nilson. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 44.955907(4). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Scandium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with scandium depend on chemical form, dose and route of exposure. Pure scandium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.