Scandium (7440-20-2) Physical and Chemical Properties
Scandium
A rare-earth transition metal used in specialty alloys, electronic materials and analytical standards for industrial R&D and procurement.
| CAS Number | 7440-20-2 |
| Family | Rare earth metals |
| Typical Form | Silvery metal — ingots, foil or powder |
| Common Grades | EP |
Scandium is a transition metal of the scandium group and is classified among the rare earth metals. It occurs as the element \(\ce{Sc}\) with atomic number 21 and exhibits the electronic configuration that places it at the head of the 3d series; this gives scandium a predominantly +3 oxidation state in stable compounds and a chemistry dominated by ionic/coordinate bonding to oxygen- and nitrogen-donor ligands. As a metallic element it shows metallic bonding with delocalized electrons, a low topological polar surface area (0), and negligible hydrogen-bonding capacity when considered in its elemental form.
Structurally, elemental scandium forms metallic crystals; its surface readily oxidizes to form the stable oxide \(\ce{Sc2O3}\), which passivates bulk metal. Finely divided or powdered scandium is more chemically reactive than bulk material: powders can be pyrophoric or readily ignitable and present inhalation and dust hazards. In aqueous and acidic media scandium behaves like other early transition metals and lanthanides—forming \(\ce{Sc^3+}\) aquo ions and hydrolysis products; its aqueous chemistry is dominated by hard Lewis-acid interactions and strong complexation with multidentate oxygen ligands.
Scandium has limited large-scale commercial use but is important in specialized sectors: tracer and analytical standards, certain semiconductor or electronic applications, and niche metallurgical applications where small additions to alloys can modify mechanical or physical properties. Common commercial grades reported for this substance include: EP.
Basic Physical Properties (Density, Melting Point, Boiling Point)
Atomic Weight
Standard computed atomic/molecular masses available for the element: molecular weight = 44.95591; exact mass = 44.955907; monoisotopic mass = 44.955907. The element is represented by the atomic formula \(\ce{Sc}\).
Appearance and Physical State
Elemental scandium is described as a silvery-white solid in bulk; experimental physical descriptions include "Dry Powder" for particulate forms and "Silvery-white solid" for bulk metal. Metallic scandium typically occurs as solid pieces, foils, ingots, or powders depending on preparation.
Density
No experimentally established value for this property is available in the current data context.
Melting Point
No experimentally established value for this property is available in the current data context.
Boiling Point
No experimentally established value for this property is available in the current data context.
Chemical Properties (Reactivity and Oxidation States)
Oxidation States
The dominant and chemically significant oxidation state of scandium in compounds is \(\ce{Sc^3+}\). In this oxidation state scandium behaves as a hard trivalent cation, forming predominantly ionic salts and coordination complexes with oxygen- and nitrogen-donor ligands. Lower oxidation states are uncommon and generally unstable under standard conditions.
Reactivity with Air and Water
Elemental scandium forms a stable oxide layer on exposure to air, principally \(\ce{Sc2O3}\), which passivates bulk metal surfaces. Finely divided scandium (powder) is substantially more reactive: particulate material is combustible and may ignite, generating particulate and oxide fumes. In contact with water, metallic scandium will corrode and form \(\ce{Sc^3+}\)-containing species; hydrolysis of aquo \(\ce{Sc^3+}\) gives polymeric/hydroxide species under less acidic conditions.
Reactivity with Acids and Bases
Scandium metal and scandium(III) compounds dissolve in mineral acids to afford \(\ce{Sc^3+}\) salts. In aqueous solution \(\ce{Sc^3+}\) undergoes hydrolysis and forms hydroxide/oxide species such as \(\ce{Sc(OH)3}\) under appropriate conditions; complex formation with chelating ligands is common. The element does not display pronounced amphoterism compared with heavier group-3 congeners, and strongly basic solutions tend to precipitate hydroxide phases or soluble complex anions depending on ligand and ionic strength.
Isotopic Composition
Stable Isotopes
Natural scandium is essentially monoisotopic, consisting predominantly of the stable isotope \(\ce{^{45}Sc}\).
Radioisotopes
Radioisotopes of scandium can be prepared for tracer and nuclear applications, but there is no significant naturally occurring radioisotope fraction present in commercial elemental material. Production and use of specific radioisotopes are governed by radiochemical practice and regulatory controls.
Thermodynamic Parameters
Heat Capacity and Related Data
No experimentally established value for this property is available in the current data context.
Enthalpy and Gibbs Energy
No experimentally established value for this property is available in the current data context.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 7440-20-2
- EC number: 231-129-2
- UNII: YUJ4U1EW7R
- ChEBI: CHEBI:33330
- DTXSID: DTXSID9064689
InChI: InChI=1S/Sc
InChIKey: SIXSYDAISGFNSX-UHFFFAOYSA-N
SMILES: [Sc]
Molecular formula (elemental): \(\ce{Sc}\)
Molecular weight: 44.95591
Synonyms and Common Names
Reported synonyms and descriptor strings include: Scandium; Sc; scandium atom; Scandium (element); Scandium Metallicum; 45Sc; Scandium-45 isotope; Scandium powder; Scandium foil; Atomic Scandium.
Industrial and Commercial Applications
Major Use Sectors
Documented sectors and processing contexts include semiconductor manufacturing and primary metal manufacturing. Scandium occurs in various accessory minerals (e.g., thortveitite, davidite) and is often recovered in small quantities from ores associated with tin, zirconium, or tungsten-bearing minerals.
Typical Application Examples
Practical uses are largely specialist: analytical and tracer standards for elemental analysis, niche roles in semiconductor or electronic research, and supply for research and development where unique electronic or metallurgical properties of \(\ce{Sc}\) are required. Reported commercial grades: EP.
If a concise application summary is not directly applicable to a specific procurement decision, selection is typically governed by the material form (foil, powder, ingot), purity, and intended analytical or metallurgical use.
Safety and Handling Overview
Storage and Handling Considerations
Powdered scandium is combustible and may ignite if dispersed as a dust or exposed to ignition sources; dust control, minimization of static discharge, and safe handling measures for flammable metal powders are appropriate. Bulk metallic scandium is less reactive due to surface passivation but should be stored dry and protected from conditions that could promote oxidation or contamination. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
Occupational Exposure and Protective Measures
Exposure control should emphasize preventing inhalation of dust and handling fine particulates under appropriate local exhaust ventilation or containment. Use of suitable personal protective equipment (PPE) — gloves, eye protection, and respiratory protection when dust generation is possible — is recommended. There are reports associating scandium exposure with fibrogenic effects; therefore, occupational hygiene measures and medical surveillance as appropriate for metal dusts should be implemented. For emergency procedures, extinguishing metal fires requires specialized methods; consult the SDS and emergency response guidance.
