Element guide
Electron configuration of Krypton (Kr)
The electron configuration of Krypton is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6. In shorthand form it is written as [Ar] 3d10 4s2 4p6.
Use this page to connect the notation with atomic number 36, the p-block, and the filled-shell pattern 4s2 4p6.
How to write the configuration
Configuration at a glance
Krypton has atomic number 36, so a neutral atom has 36 electrons. The configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 is a compact record of where those electrons sit by subshell.
The shorthand [Ar] 3d10 4s2 4p6 replaces the filled inner core with the previous noble gas. That notation keeps attention on the electrons that usually explain bonding, ions, and periodic trends.
Krypton as a noble gas
Krypton is a noble gas in period 4, group 18. Its electron configuration shows a completely filled 4p subshell (4p6), which gives it chemical stability. The complete sequence of filling for Kr is:
1s2 (2) → 2s2 (4) → 2p6 (10) → 3s2 (12) → 3p6 (18) → 4s2 (20) → 3d10 (30) → 4p6 (36)
Notice that 3d fills after 4s but before 4p. The 3d10 contributes 10 electrons and sits between the 4s and 4p in the filling order.
Step-by-step filling walkthrough: 1. Start with atomic number 36. 2. Follow the Aufbau sequence through the entire 4p subshell. 3. The 3d10 subshell fills completely (10 electrons across five d orbitals). 4. The 4p6 subshell receives the final 6 electrons. 5. Verify: add every superscript and confirm the total equals 36.
Orbital diagram and valence meaning
An orbital diagram turns each subshell into boxes and arrows. As a noble gas, Kr has all electrons paired with no unpaired electrons. The filled 4p6 gives Kr a full octet in its outer shell, explaining its low chemical reactivity.
Common mistakes
The first mistake is skipping the 3d10 contribution. Many configurations list 3d10 between 4s2 and 4p6. Verify the total carefully. The second mistake is treating Kr as completely inert. While Kr is less reactive than lighter noble gases, it does form some compounds with highly electronegative elements like fluorine.
Krypton reference table
| Item | Value |
|---|---|
| Atomic number | 36 |
| Full configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 |
| Noble-gas notation | [Ar] 3d10 4s2 4p6 |
| Valence clue | 4s2 4p6 |
| Block | p-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 36 for a neutral Krypton 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 Krypton?
The neutral Krypton atom is written as 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6. The shorthand form is [Ar] 3d10 4s2 4p6.
How many valence electrons does Krypton have?
As a noble gas with configuration 4s2 4p6, Krypton has a complete octet of 8 valence electrons in its outer shell.
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.
Does Krypton form chemical compounds?
Krypton can form compounds with fluorine, such as KrF2, though it is much less reactive than lighter noble gases like xenon.
Practice nearby concepts
Study notes and practice checks
From answer to understanding
Krypton is an important reference point in electron configuration study because its filled 4s2 3d10 4p6 configuration serves as the noble-gas core shorthand for all elements in period 5 (Rb through Xe).
Practice comparison
Compare Krypton (Kr) with Bromine (Br) and Rubidium (Rb). Br: [Ar] 3d10 4s2 4p5 (one electron short of Kr), Kr: [Ar] 3d10 4s2 4p6 (full octet), Rb: [Kr] 5s1 (one electron beyond Kr). This pattern shows the noble gas as a stability boundary.
Teacher and self-study notes
Use Kr as a teaching example for octet stability. Its complete filling of the 4p subshell makes it the natural noble gas reference for period 5 elements, just as Ar serves period 4.
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