Strontium (Sr)
Element 38 · Alkaline earth metal · atomic mass 87.62 u · group 2, period 5
Electron shells: 2, 8, 18, 8, 2
Strontium burns brilliant red, which is why it dominates fireworks and emergency flares. Its chemistry mimics calcium closely enough that the body files it into bone.
Because bone mistakes it for calcium, strontium-90 fallout was the great fear of 1950s nuclear testing.
- Atomic number
- 38
- Atomic mass
- 87.62 u
- Electron configuration
- [Kr] 5s²
- Group · period · block
- 2 · 5 · s
- Oxidation states
- +2
- Electronegativity
- 0.95 (Pauling)
- Melting point
- 777 °C
- Boiling point
- 1,382 °C
- Density
- 2.64 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-yellow metal
- Discovered
- Adair Crawford and William Cruickshank, 1790
38 protons, and 38 electrons when neutral
IUPAC standard atomic weight
Alkaline earth metals
What Strontium is used for
- Red fireworks and flares
- Ferrite ceramic magnets
- Glow-in-the-dark pigments
- Osteoporosis treatment research
Atomic structure of Strontium
A neutral strontium atom has 38 protons and 38 electrons. Its most common isotope carries about 50 neutrons, which is where the mass number 88 comes from. Change the neutron count and you have a different isotope of strontium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 8, 2. In orbital notation that is [Kr] 5s², leaving 2 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Strontium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Strontium sits in the periodic table
Group 2 metals with two outer electrons. Harder and less reactive than the alkali metals, and they form the +2 ions that build bone, shell and cement.
Discovery and naming
Strontium was discovered by Adair Crawford and William Cruickshank in 1790. Its name comes from Strontian, a village in Scotland, which is also why its symbol (Sr) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Strontium?
The standard atomic weight of Strontium is 87.62 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Strontium have?
Strontium has 38 protons, because the atomic number is the proton count and that is what makes an atom Strontium at all. A neutral Strontium atom has the same number of electrons, 38. The neutron count varies by isotope; the most common one has about 50, since 88 − 38 = 50.
What is the electron configuration of Strontium?
The electron configuration of Strontium is [Kr] 5s². Its electrons are arranged 2, 8, 18, 8, 2 across 5 shells.
Is Strontium a metal?
Yes. Strontium is classified as a alkaline earth metal, on the left side of the table.
What group and period is Strontium in?
Strontium is in group 2 (the alkaline earth metals), period 5, in the s-block. The group is its column and the period is its row.
What is the charge of Strontium?
Strontium most commonly forms a 2+ ion. It has 2 electrons in its outer shell and loses them readily, which is what the group number tells you.
What is the melting point of Strontium?
Strontium melts at 777 °C and boils at 1,382 °C. That puts it in the solids at everyday temperatures.
What is Strontium used for?
Red fireworks and flares, Ferrite ceramic magnets, Glow-in-the-dark pigments, Osteoporosis treatment research. Strontium burns brilliant red, which is why it dominates fireworks and emergency flares.
Who discovered Strontium, and where does its name come from?
Strontium (Sr) was discovered by Adair Crawford and William Cruickshank in 1790. The name comes from Strontian, a village in Scotland.