Elements

Electron configuration of Strontium (Sr)

Read the Strontium electron configuration, noble-gas shorthand, valence shell, orbital filling logic, and the mistakes to avoid when writing Sr.

Guide: Guía práctica Read: 5 min Updated: 2026-06-27

Element guide

Electron configuration of Strontium (Sr)

The electron configuration of Strontium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2. In shorthand form it is written as [Kr] 5s2.

Use this page to connect the notation with atomic number 38, the s-block, and the valence pattern 5s2.

How to write the configuration

Configuration at a glance

Strontium has atomic number 38, so a neutral atom has 38 electrons. The configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2 records where those electrons sit by subshell.

The shorthand [Kr] 5s2 replaces the filled krypton core with the noble-gas symbol. The remaining 5s2 are the outer electrons.

Step-by-step filling

After the argon core (18 electrons), the filling continues through the first transition series (3d10), then 4p6, and finally 5s2. Krypton accounts for 36 electrons (through 4p6), leaving 2 electrons to place in the 5s subshell.

Step-by-step filling walkthrough: 1. Start with atomic number 38. 2. Fill through krypton: up to 4p6 (36 electrons). 3. Place 2 electrons in 5s (38 electrons total). 4. The 5s2 are the only outer electrons. 5. Verify: add every superscript and confirm the total equals 38.

Orbital diagram and valence meaning

An orbital diagram turns each subshell into boxes and arrows. Sr has all electrons paired with no unpaired electrons. The 5s2 electrons are the valence electrons, and Sr readily loses both to form Sr2+.

Strontium is an alkaline earth metal (group 2) and behaves similarly to calcium and barium. Its 5s2 configuration means it forms Sr2+ ions in virtually all its compounds.

Common mistakes

The first mistake is miscounting the electrons after krypton. Kr is 36, 5s2 makes 38. The second mistake is forgetting that the 4d and 4f subshells are empty for Sr. The next electrons would go into 4d, but Sr stops at 5s2.

A third common error is confusing Sr with transition metals. Although Sr is near the d-block, it is an s-block element with a simple 5s2 valence configuration.

Strontium reference table

Item Value
Atomic number 38
Full configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2
Noble-gas notation [Kr] 5s2
Valence clue 5s2
Block s-block

Use the table as a learning reference, then verify advanced oxidation-state questions with your course material.

Before you submit an answer

  • The superscripts add up to 38 for a neutral Strontium atom.
  • The notation follows the filling order used in your course.
  • The last occupied subshell matches the periodic-table block.
  • Any transition-metal or actinide exception is checked against a reference.
  • The shorthand core is a noble gas, not a random previous element.

Common questions

What is the electron configuration of Strontium?

The neutral Strontium atom is written as 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2. The shorthand form is [Kr] 5s2.

How many valence electrons does Strontium have?

Start from the outer-shell clue 5s2. For main-group elements this gives a direct valence count of 2 valence electrons.

Should I memorize this configuration?

Memorize the filling pattern first. Individual configurations become easier when you can rebuild them from atomic number, noble-gas cores, and periodic-table position.

What is the common ion of Strontium?

Strontium forms Sr2+ by losing both 5s electrons, achieving the stable electron configuration of Krypton [Kr].

Study notes and practice checks

From answer to understanding

Strontium is a good example of an s-block element in period 5. Its configuration [Kr] 5s2 shows the same pattern as Calcium ([Ar] 4s2) and Barium ([Xe] 6s2), confirming the group 2 pattern.

Practice comparison

Compare Strontium (Sr) with Rubidium (Rb) and Yttrium (Y). Rb: [Kr] 5s1, Sr: [Kr] 5s2, Y: [Kr] 4d1 5s2. The s-block fills completely (5s2) before the d-block begins at Yttrium.

Teacher and self-study notes

Strontium compounds produce a bright red flame color, used in fireworks and flares. Its straightforward [Kr] 5s2 configuration makes it a useful example when teaching the period 5 s-block elements.

Elena Marquez

Autora de la guia

Elena Marquez

Chemistry educator and study-guide editor

Elena explains electron configurations, orbital diagrams, and periodic trends for learners who need clear steps before memorization. Her guides focus on counting, notation, and common classroom mistakes.

Credenciales: Editorial specialization in introductory chemistry, periodic trends, and student reference material.

Experiencia: More than eight years preparing practical chemistry explainers, worksheets, and reference material for independent learners.

Actualizado: 2026-06-27 Politica editorial Correcciones

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