Technetium (7440-26-8) Physical and Chemical Properties
Technetium
Elemental technetium is a radioactive transition metal used in isotope production and specialist metallurgical applications; procurement and handling require defined isotopic specifications and radiation controls.
| CAS Number | 7440-26-8 |
| Family | Transition metal (radionuclide) |
| Typical Form | Silver-gray metallic solid |
| Common Grades | EP |
Technetium is a transition metal of the manganese group (period 5, group 7) with atomic number 43. It is the lightest element with no stable isotopes; all known nuclides are radioactive. Structurally the element adopts a close-packed hexagonal (hcp) metallic lattice and is chemically and electronically analogous to rhenium and manganese to a lesser extent, displaying variable valence and strong propensity to form oxoanions and high oxidation-state fluorides. The neutral atom is represented by the formula Tc and by the elemental symbol Tc.
Electronically, technetium has an incompletely filled d–subshell that enables a range of oxidation states, notably high positive oxidation states that stabilize oxo- and fluoro-species (for example pertechnetate, \((\mathrm{TcO}_4)^{-}\), and TcF5/TcF6 fluorides). As a metal it is moderately heavy and refractory: metallic technetium is silver–gray, corrodes slowly in moist air, and exhibits high melting and boiling points characteristic of refractory transition metals. Chemically it shows amphoteric behaviour in the sense that it dissolves in oxidizing mineral acids and strong oxidizing agents to give soluble oxo-species, but it is not attackable by non-oxidizing hydrochloric acid.
Technetium has important practical relevance in nuclear technology and medicine. As a fission product it contributes to long-term radioactivity in spent fuel (notably \({}^{99}\mathrm{Tc}\) with a long half-life), and the metastable isomer \({}^{99\mathrm{m}}\mathrm{Tc}\) has extensive use as a diagnostic radiopharmaceutical due to its convenient gamma emission and short half-life.
Common commercial grades reported for this substance include: EP.
Basic Physical Properties (Density, Melting Point, Boiling Point)
Atomic Weight
Standard atomic mass (reported): 96.90636.
Appearance and Physical State
Metallic technetium is described as a silver‑gray metal often obtained as a spongy mass when reduced from ammonium pertechnetate; it tarnishes slowly in moist air. The crystal structure is close‑packed hexagonal (hcp), isomorphous with rhodium, ruthenium and osmium.
Density
Reported density: \(11\,\mathrm{g}\,\mathrm{cm}^{-3}\).
Melting Point
Reported melting point: \(2157\,^\circ\mathrm{C}\).
Molar enthalpy of fusion at the melting point: \(33.29\,\mathrm{kJ}\,\mathrm{mol}^{-1}\).
Boiling Point
Reported boiling point (elemental): \(4265\,^\circ\mathrm{C}\).
Extrapolated vapor pressure values (reported): 1 Pa at \(2454\,^\circ\mathrm{C}\); 10 Pa at \(2725\,^\circ\mathrm{C}\); 100 Pa at \(3051\,^\circ\mathrm{C}\); 1 kPa at \(3453\,^\circ\mathrm{C}\); 10 kPa at \(3961\,^\circ\mathrm{C}\); 100 kPa at \(4621\,^\circ\mathrm{C}\). All vapor‑pressure values are noted as extrapolated.
Chemical Properties (Reactivity and Oxidation States)
Oxidation States
Common oxidation states reported for technetium include +4 and +7 (the latter present in the pertechnetate ion, \((\mathrm{TcO}_4)^{-}\)); +3 is less common. Technetium exhibits polyvalency typical of early-to-mid transition metals, with accessible high oxidation states that stabilize oxo- and fluoro-complexes.
Reactivity with Air and Water
Metallic technetium tarnishes slowly in moist air. Under oxidizing conditions it is converted to higher oxides and soluble oxo-species. In aqueous chemistry, oxidizing agents readily produce pertechnetate \((\mathrm{TcO}_4)^{-}\), a relatively mobile and soluble oxyanion; reduction yields lower-valent insoluble oxides or metal.
Reactivity with Acids and Bases
Technetium dissolves in oxidizing acids such as nitric acid, aqua regia and concentrated sulfuric acid to give soluble technetium species; it is reported as not soluble in hydrochloric acid of any strength. Neutral or alkaline hydrogen peroxide solutions dissolve technetium to give solutions containing the pertechnetate ion \((\mathrm{TcO}_4)^{-}\). The metal reacts directly with fluorine to form penta‑ and hexafluorides, combines with sulfur at ambient temperature to form disulfide species, and can form carbides (TcC) under appropriate conditions.
Isotopic Composition
Stable Isotopes
No stable isotopes exist for technetium. All isotopes are radioactive.
Radioisotopes
Technetium has multiple radioisotopes of practical interest. The metastable isomer \({}^{99\mathrm{m}}\mathrm{Tc}\) (decay product of \({}^{99}\mathrm{Mo}\)) has a half‑life of about 6 hours and is widely used as a diagnostic radioactive imaging agent. The ground state \({}^{99}\mathrm{Tc}\) (decay product of \({}^{99\mathrm{m}}\mathrm{Tc}\)) has a long half‑life reported as 210,000 years and is a significant long‑lived fission product in spent nuclear fuel. The most commonly available isotope in practice is \({}^{99}\mathrm{Tc}\).
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
Molar enthalpy of fusion at the reported melting point: \(33.29\,\mathrm{kJ}\,\mathrm{mol}^{-1}\).
No concise Gibbs free energy values for standard formation or other thermodynamic functions are available in the current data context.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 7440-26-8
- EC number: 231-136-0
- ChEBI: CHEBI:33353
- DSSTox Substance ID: DTXSID5075028
- Nikkaji number: J95.292C
- Wikidata: Q1054
Additional computed identifiers:
- Molecular formula: Tc
- Molecular / atomic weight: 96.90636
- InChI: InChI=1S/Tc
- InChIKey: GKLVYJBZJHMRIY-UHFFFAOYSA-N
- SMILES: [Tc]
Synonyms and Common Names
Available synonyms and name variants reported include: Technetium; TECHNETIUM; Technetium, elemental; Tc; technetium atom; Technetium (element); Technetium (atomic); 43Tc; Technetium element. (This list is a selection of recorded synonyms.)
Industrial and Commercial Applications
Major Use Sectors
Technetium’s principal relevance is in nuclear medicine (diagnostic radiopharmaceuticals based on \({}^{99\mathrm{m}}\mathrm{Tc}\)) and nuclear technology (fission product in reactor fuel and waste management concerns, particularly \({}^{99}\mathrm{Tc}\)). Small additions of technetium have been investigated as corrosion inhibitors in steel manufacturing, although routine industrial use is limited by radioactivity concerns. Technetium and certain alloys have been studied in low‑temperature superconductivity and related cryogenic applications.
Typical Application Examples
- Diagnostic imaging: use of \({}^{99\mathrm{m}}\mathrm{Tc}\) radiopharmaceuticals for gamma imaging.
- Nuclear industry: technetium is produced as a fission product and is a long‑term radiological contaminant in spent fuel and waste streams (\({}^{99}\mathrm{Tc}\) of particular environmental concern).
- Metallurgy: experimental use as a microalloying element or corrosion inhibitor in steel production (application constrained by radioactivity).
- Chemical reagents: formation of pertechnetate \((\mathrm{TcO}_4)^{-}\) in oxidizing aqueous chemistry; formation of fluorides and other high‑oxidation‑state compounds in specialised syntheses.
If a purchaser or process engineer requires a concise usage summary tailored to a specific sector, selection should be based on the elemental and radiochemical properties described above.
Safety and Handling Overview
Storage and Handling Considerations
Technetium is radioactive; handling and storage must follow accepted radiological protection practices (time, distance, shielding) and local regulatory requirements. Solid metallic technetium should be stored in containers appropriate for radioactive materials with measures to prevent dispersion and contamination. Solutions containing pertechnetate or other soluble technetium compounds require secondary containment and engineered controls to prevent environmental release and personnel uptake.
For materials that can form aerosols or fine particulates, avoid generation of airborne 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
Pertechnetate (\((\mathrm{TcO}_4)^{-}\)) exhibits significant gastrointestinal absorption (reported 50–80% for pertechnetate), and soluble technetium species can be systemically distributed; insoluble oxides and particulates clear more slowly from the lung. General occupational controls include engineered containment, local exhaust ventilation, contamination monitoring, and access controls. Personal protective equipment should include disposable or decontaminable gloves, eye protection, and laboratory clothing; respiratory protection is required when there is a risk of inhalation of particulates or aerosols. Decontamination procedures and medical response plans should be in place; familiar emergency first‑aid measures for radiological exposures are recommended.
Emergency medical management principles for contamination and ingestion are standard: decontamination, supportive care (airway, breathing, circulation), and specialized radiological consultation for decorporation and dose assessment. For radioactive materials, follow institutional radiation safety protocols and coordinate with health physics/radiation protection personnel.
For regulatory limits and specific exposure criteria, refer to applicable regulatory authorities and institutional radiation protection programs.
