Strontium
Definition and meaning of Strontium in chemistry.
![Strontium element card: symbol Sr, atomic number 38, atomic mass 87.62, electron configuration [Kr] 5s², oxidation states +2, Alkaline earth metal, group 2, period 5, solid at room temperature.](/assets/images/terms/strontium-chemical-element.webp)
Strontium is a highly reactive alkaline earth metal with the symbol Sr and atomic number 38. It exists as a shiny, silvery-white metal in its pure, elemental form. However, the metal quickly develops a dull yellowish tint when it is exposed to the open air.
In more detail
Strontium sits in group 2 of the periodic table, directly between calcium and barium. It shares chemical properties with these vertical neighbors because they all have two valence electrons. Strontium is softer than calcium and shows an even greater chemical reactivity.
The metal reacts vigorously and bubbles rapidly when placed in liquid water. This reaction produces strontium hydroxide, Sr(OH)2, and flammable hydrogen gas. When it is exposed to oxygen in the air, strontium oxidizes very rapidly.
It forms a dark, dull surface layer of strontium oxide, SrO. This reactivity means chemists must store pure strontium under protective mineral oil. In nature, strontium is found in minerals like celestine and strontianite.
The atom easily loses its two outer electrons to form a stable Sr2+ cation. A cation is simply an atom that carries a positive electrical charge. A common student mistake is confusing strontium with its neighbor, sodium. However, strontium is a divalent alkaline earth metal, while sodium is a monovalent alkali metal.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Sr |
| Atomic number | 38 |
| Atomic mass | 87.62 u |
| Category | Alkaline-Earth-Metal |
| State at room temperature | Solid |
| Melting point | 777 degrees Celsius |
Strontium compounds are widely used in commercial fireworks and emergency road flares. Chemists choose these compounds because they emit a brilliant red light when heated. When strontium electrons absorb heat energy, they jump to higher energy levels. As they cool, they fall back down and release this energy as red light waves. This bright color helps people see emergency signals from very far away. Strontium carbonate is the specific compound most manufacturers use to create this crimson flame. This application shows how simple electron transitions can produce bright, visible colors.
Frequently asked questions
What is the radioactive isotope strontium-90?
Strontium-90 is a dangerous radioactive isotope produced during nuclear fission. It poses a health risk because the body mistakes it for calcium and absorbs it into bones.
Is natural strontium safe for humans to handle?
Stable strontium compounds are generally safe and have very low toxicity. However, pure strontium metal reacts quickly with moisture on skin and can cause chemical burns.
Why does strontium color a flame red?
Heat excites strontium electrons, pushing them to higher energy levels. When the electrons return to their ground state, they release energy as red light.
Related terms
Sources & references
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