Chemical element · reference page

38Sr

Strontium

Strontium is element 38 (Sr), located in period 5, group 2 and the s block. At room temperature its reference phase is solid. Its electron configuration is [Kr] 5s2.

Atomic number38

Standard atomic weight87.62(1)

Group2

Period5

Blocks

Electron configuration[Kr] 5s2

Electronic structure

What controls its chemistry

The outer configuration ends in s². Removing two valence electrons produces a +2 ion, which is the characteristic ionic state of the alkaline-earth metals.

Compared with group 1 metals, the two-electron outer shell changes ionisation energies, bonding and reactivity. Their compounds commonly occur as oxides, carbonates, sulfates or halides rather than as free metals in nature.

Chemical forms

Compounds, ions and materials

The +2 oxidation state dominates. Oxides, hydroxides, halides, carbonates and sulfates are common families of strontium compounds, although their solubility and thermal stability vary systematically down group 2.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 2.64 g/cm³. The melting point is 1 041 K (767.9 °C). The boiling point is 1 650 K (1 377 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where strontium is found and used

In practice, strontium is encountered in fireworks, magnets and medical applications.

In practice

Examples of real uses

Fireworks

Strontium compounds can produce characteristic colours, sparks or energetic effects when heated in pyrotechnic mixtures.

Magnets

Strontium is used in magnetic materials where strong, stable or temperature-resistant magnetism is required.

Medical applications

Strontium is used in selected medicines, implants, diagnostics or treatment technologies; the chemical or isotopic form is crucial.

Periodic position

What its neighbours tell us

Strontium is in period 5 and group 2. In the neighbourhood shown here, it lies between rubidium and yttrium in the same period; calcium is above it and barium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationalkaline earth metal

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 8 · 2

Density2.64 g/cm³

Melting point1 041 K (767.9 °C)

Boiling point1 650 K (1 377 °C)

Pauling electronegativity0.95

First ionisation energy549.5 kJ/mol

Electron affinity5.023 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of strontium is associated with William Cruickshank (chemist). Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 87.62(1). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Strontium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with strontium depend on chemical form, dose and route of exposure. Pure strontium, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.