Strontium
Atomic Data
| Atomic Number | 38 |
| Symbol | Sr |
| Atomic Weight | 87.62 u |
| Density (STP) | 2.64 g/cm³ |
| Melting Point | 776.85 °C (1050 K) |
| Boiling Point | 1381.85 °C (1655 K) |
| Electronegativity | 0.95 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2 |
| Oxidation States | +2 |
| Phase at STP | Solid |
| Category | Alkaline-Earth Metal |
| Period / Group | 5 / 2 |
| CAS Number | 7440-24-6 |
Electron Configuration
[Kr] 5s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| O | 5 | 5s | 2 | 38 |
| Total | 38 | 38 | ||
Isotopes of Strontium
Strontium has four naturally occurring stable isotopes. The most abundant is ⁸⁸Sr, comprising 82.58% of all naturally occurring Strontium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Strontium-84 | ⁸⁴Sr | 38 | 46 | 0.56 | Stable |
| Strontium-86 | ⁸⁶Sr | 38 | 48 | 9.86 | Stable |
| Strontium-87 | ⁸⁷Sr | 38 | 49 | 7.0 | Stable |
| Strontium-88 | ⁸⁸Sr | 38 | 50 | 82.58 | Stable |
Abundance & Occurrence
Strontium is present in Earth's crust at approximately 370 ppm by mass and at approximately 4 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Water reactivity: Strontium metal reacts with water to produce strontium hydroxide and hydrogen gas; the reaction is less violent than rubidium or caesium but can still ignite the evolved hydrogen.
- Fire hazard: Strontium powder and turnings are flammable; strontium fires require Class D extinguishing agents: water must not be used.
- Strontium-90: radiation hazard: Sr-90, a radioactive fission product with a 28.8-year half-life, is a high-energy beta emitter that accumulates in bone (mimicking calcium); it is among the most radiologically hazardous long-lived fission products.
- Flares and pyrotechnics: Strontium salts produce brilliant crimson flames and are used in fireworks and signal flares; smoke and fume inhalation from burning strontium compounds should be avoided.
Strontium in the Real World
Real-World Uses
- Fireworks (crimson red): Strontium nitrate and strontium carbonate burn to produce the distinctive crimson-red colour of fireworks, flares, and signal rockets; the colour arises from strontium emission lines in the red part of the visible spectrum.
- Ferrite magnets: Strontium ferrite (SrFe₁₂O₁⁹) is the most widely produced permanent magnet material by volume, used in loudspeakers, refrigerator door seals, motor magnets in small appliances, and magnetic strip cards.
- Nuclear medicine imaging: Strontium-89 (Metastron) is a beta-emitting radiopharmaceutical used for palliative treatment of bone metastases pain; it concentrates in bone similarly to calcium and delivers a localised radiation dose to tumour sites.
- Toothpaste for sensitive teeth: Strontium chloride and strontium acetate block dentinal tubules that expose nerve endings in sensitive teeth, providing relief from pain triggered by hot, cold, sweet, or acidic stimuli.
- Isotope geochemistry: The strontium-87/strontium-86 ratio is used to date rocks, trace magma sources, determine the provenance of ancient artefacts and food, and study ocean circulation and diagenesis in sedimentary geology.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is strontium used for?
Strontium compounds have historically been used in the red-coloured flames of fireworks and signal flares: strontium salts produce a vivid crimson when burned. Strontium titanate was once used as a diamond simulant. Strontium ranelate was used as a medication for osteoporosis. Strontium-90, a radioactive isotope, powers radioisotope thermoelectric generators (RTGs) and has been used in cancer treatment.
Is strontium radioactive?
Natural strontium is not radioactive: it consists of four stable isotopes. However, strontium-90 is a dangerous radioactive isotope produced in nuclear fission. It is chemically similar to calcium and readily incorporates into bone if ingested, where its beta radiation can cause bone cancer and leukaemia. Strontium-90 is one of the main long-term radiation hazards from nuclear weapons fallout and reactor accidents.
How was strontium discovered?
Strontium was identified as a new element in 1790 by Adair Crawford and William Cruikshank, who found it in a mineral from the village of Strontian in Scotland: the source of its name. The metal itself was first isolated in 1808 by Humphry Davy using electrolysis, the same technique he used to isolate several other alkaline earth metals.
Why is strontium-90 so dangerous in nuclear fallout?
Strontium-90 is dangerous because it behaves chemically like calcium and is incorporated into teeth and bones, particularly in children during growth. Once deposited in bone, it delivers continuous beta radiation to bone marrow over its 29-year half-life, substantially increasing the risk of bone cancer and leukaemia. This is why monitoring strontium-90 levels in soil, milk, and human bone was a major concern during the Cold War nuclear testing era.