Quick Facts
| Property | Value |
|---|---|
| Symbol | Sr |
| Atomic Number | 38 |
| Atomic Mass | 87.62 u |
| Category | Alkaline Earth Metal |
| Period | 5 |
| Group | 2 |
| Block | s |
| Electron Configuration | [Kr] 5s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 2.64 g/cm³ |
| Melting Point | 777°C (1050 K) |
| Boiling Point | 1377°C (1650 K) |
| Appearance | Silvery-white, yellowish tinge |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 5s² |
| Electronegativity | 0.95 (Pauling scale) |
| First Ionization Energy | 549.5 kJ/mol |
| Atomic Radius | 215 pm |
| Covalent Radius | 195 pm |
| Van der Waals Radius | 249 pm |
History and Discovery
Discovered by: William Cruickshank (identified), Humphry Davy (isolated) Year of Discovery: 1790 (identified), 1808 (isolated) Location: Scotland and England
Etymology
Named after Strontian, a village in the Scottish Highlands where the mineral strontianite was first found.
Discovery Story
In 1790, Adair Crawford and William Cruickshank recognized strontium as a new element in the mineral strontianite. Thomas Charles Hope confirmed it was distinct from barium. Humphry Davy isolated metallic strontium in 1808 by electrolysis of strontium chloride.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁸⁴Sr | 0.56% | Stable | - |
| ⁸⁶Sr | 9.86% | Stable | - |
| ⁸⁷Sr | 7.00% | Stable | - |
| ⁸⁸Sr | 82.58% | Stable | - |
Occurrence
Natural Abundance
Strontium comprises about 370 ppm of Earth's crust. It is never found free in nature. Main ores are celestine (SrSO₄) and strontianite (SrCO₃). Major producers are China, Spain, and Mexico.
Extraction and Production
- Roasting: Celestine with carbon to form strontium sulfide
- Electrolysis: Of molten strontium chloride for metal
- Sources: Celestine mining
- Global production: about 300,000 tons (as celestine)
Applications and Uses
Pyrotechnics
- Fireworks and signal flares (brilliant red flame)
- Military pyrotechnics
- Emergency flares
Electronics
- Cathode ray tube (CRT) glass (blocks X-rays)—declining use
- Ferrite magnets (strontium hexaferrite)
- Ceramic capacitors
Industrial Applications
- Zinc refining
- Glass and ceramic colorant
- Sugar beet processing
Other Uses
- Toothpaste for sensitive teeth (strontium chloride)
- Strontium ranelate for osteoporosis
Biological Role
Strontium has no essential biological role but is incorporated into bones due to its similarity to calcium.
In the Human Body
- About 320 mg in adult body
- 99% in bones and teeth
- Substitutes for calcium in bone
- May promote bone health
Medical Uses
Strontium ranelate was used for osteoporosis treatment (now restricted due to side effects).
Safety and Hazards
Toxicity
Stable strontium compounds have low toxicity. Strontium-90 (radioactive) is highly dangerous as it accumulates in bones.
Handling Precautions
- Metal reacts with water and air
- Store under mineral oil
- Dust can ignite
- Strontium-90 from nuclear fallout is a serious health hazard
Environmental Impact
Strontium-90 from nuclear testing contaminated the environment. It accumulates in bones and can cause bone cancer and leukemia.
Interesting Facts
- The brilliant red color of some fireworks comes from strontium compounds
- Strontium-90 from nuclear fallout in the 1950s-60s caused worldwide concern
- Strontium is so similar to calcium that the body incorporates it into bones
- The first atomic clock was based on strontium
- Strontium compounds were once used in luminous paints for watch dials