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Strontium is a chemical element on the periodic table with the atomic symbol Sr, atomic number 38, and standard atomic weight 87.62 u. Classified as a Alkaline Earth within Group 2 and Period 5 (s-block), strontium possesses a ground-state electron configuration of [Kr] 5s² distributed across 5 concentric Bohr electron shells (2 · 8 · 18 · 8 · 2) with 2 outer-shell electrons. Alkaline earth metal that burns with a brilliant crimson flame. Acantharian marine radiolarians construct their entire radial skeletons out of pure celestite (strontium sulfate, SrSO₄), and ⁸⁷Sr/⁸⁶Sr ratios trace paleoclimate weathering.

⚛️ Interactive Periodic Table Lab: Explore Strontium (Sr, Z = 38) in the CRV Science Dynamic Periodic Table & Bohr Orbital Lab to visualize its animated 2 · 8 · 18 · 8 · 2 electron shells, simulate live phase transitions from 0 K to 6,000 K, and compare periodic heatmaps across all 118 IUPAC elements.

Electron Shell Architecture and Ground-State Configuration

A neutral atom of strontium contains 38 protons in its atomic nucleus balanced by 38 electrons occupying quantized atomic orbitals. In the Bohr-Sommerfeld and quantum-mechanical orbital models, these electrons populate 5 principal energy shells (K (n=1): 2e⁻, L (n=2): 8e⁻, M (n=3): 18e⁻, N (n=4): 8e⁻, O (n=5): 2e⁻), terminating in the spherical s-orbital (azimuthal quantum number l = 0) with ground-state configuration [Kr] 5s². Removing the most loosely bound valence electron from an isolated gaseous strontium atom requires a first ionization energy of 550 kJ/mol, while its tendency to attract shared bonding electrons is quantified by a Pauling electronegativity of 0.95.

Periodic Table Position and Neighboring Elements

Within the periodic table, Strontium occupies Period 5, Group 2 of the s-block (Alkaline Earth Metals). Along Period 5, it is flanked by Rubidium (Rb, Z = 37) and Yttrium (Y, Z = 39). Vertically within its periodic family, Strontium shares valence orbital symmetry and homologous chemical trends with Beryllium (Be), Magnesium (Mg), Calcium (Ca), Barium (Ba). Learners can interactively compare Strontium's orbital radii, ionization energy, and Pauling electronegativity against all neighboring elements in the Dynamic Periodic Table Lab.

Standard Phase, Melting Point, and Boiling Point Dynamics

At standard ambient temperature and pressure (298.15 K / 25 °C, 1 atm), elemental strontium exists as a crystalline solid. As thermal energy increases, its crystal or molecular lattice undergoes solid-to-liquid fusion at a melting point of 1,050 K (+776.85 °C / +1430.3 °F) and transitions to the vapor phase at a normal boiling point of 1,650 K (+1376.85 °C / +2510.3 °F), spanning a liquid thermodynamic range of 600 K. In the CRV Science Dynamic Periodic Table, dragging the live temperature slider between absolute zero (0 K) and solar-photosphere temperatures (6,000 K) dynamically tracks Strontium's state transitions in real time alongside enthalpy and entropy phase equilibria.

Quantitative Atomic and Thermodynamic Parameter Matrix

Characteristic Oxidation States and Coordination Chemistry

As a Group 2 s-block alkaline earth metal, its two valence s-electrons are readily ionized to achieve a noble-gas configuration, yielding divalent +2 cations with higher charge density and lattice enthalpy than neighboring Group 1 alkali metals. In chemical compounds, strontium exhibits characteristic oxidation states of +2. Depending on the electronegativity difference (Δχ) of its bonding partners—such as Oxygen (χ = 3.44), Fluorine (χ = 3.98), Chlorine (χ = 3.16), Nitrogen (χ = 3.04), Carbon (χ = 2.55), or Hydrogen (χ = 2.20)—strontium forms redox-specific oxides, halides, hydrides, or coordination complexes governed by Gibbs free energy (ΔG = ΔH − TΔS).

Nucleosynthesis, Discovery History, and Elemental Origins

First identified or isolated in 1790, Strontium carries a distinct cosmological and geochemical signature. With atomic number Z = 38 beyond the iron-56 binding-energy peak, strontium is synthesized astrophysically via neutron-capture nucleosynthesis—combining slow neutron capture (the s-process in asymptotic giant branch stars) and rapid neutron capture (the r-process in neutron-star mergers and core-collapse supernovae).

Biochemical Classification: Specialized / Ultra-Trace Bio-Element

In comparative biochemistry and systems physiology, Strontium is classified as Specialized / Ultra-Trace Bio-Element. Utilized by specialized lineages (e.g., diatom silica frustules, tunicate vanabins, methanogen nickel cofactors, nitrogenase). Across terrestrial and marine ecosystems, its chemical speciation interacts with enzymes, biogeochemical cycle, phytoplankton, archaea.

Key Mechanistic Functions and Technological Uses

Alkaline earth metal that burns with a brilliant crimson flame. Acantharian marine radiolarians construct their entire radial skeletons out of pure celestite (strontium sulfate, SrSO₄), and ⁸⁷Sr/⁸⁶Sr ratios trace paleoclimate weathering. Researchers and students can further investigate Strontium's functional role alongside all 118 elements by launching the Interactive Periodic Table & Element Detective Lab on CRV Science Learn.

What is the electron configuration and valence shell structure of Strontium (Sr)?

Strontium (atomic number Z = 38) has the ground-state electron configuration [Kr] 5s², distributing its 38 electrons across 5 shells as 2 · 8 · 18 · 8 · 2. Its outermost shell contains 2 electrons, placing Strontium in Group 2, Period 5 (s-block) as a member of the Alkaline Earth Metals. You can watch these 38 electrons orbit the nucleus in real time in the Dynamic Periodic Table Bohr Lab.

What phase of matter is Strontium at room temperature, and when does it melt or boil?

At standard room temperature (298 K / 25 °C) and 1 atm pressure, Strontium is a crystalline solid. It melts at 1,050 K (+776.85 °C / +1430.3 °F) and boils at 1,650 K (+1376.85 °C / +2510.3 °F). Using the 0–6,000 K temperature slider in the Interactive Periodic Table, you can observe Strontium's exact solid, liquid, and gas transitions relative to all other elements.

How does Strontium function in biochemistry, materials science, and technology?

Alkaline earth metal that burns with a brilliant crimson flame. Acantharian marine radiolarians construct their entire radial skeletons out of pure celestite (strontium sulfate, SrSO₄), and ⁸⁷Sr/⁸⁶Sr ratios trace paleoclimate weathering. In biological systems, it is categorized under Specialized / Ultra-Trace Bio-Element, with principal oxidation states of +2 and a first ionization energy of 550 kJ/mol.