---
title: "Krypton (Kr) — element 36"
description: "Krypton is element 36, symbol Kr, atomic weight 83.798. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/krypton/
site: "At One Place"
---

# Krypton (Kr)

**Krypton — element 36: Kr**

83.798 u · Noble gas · period 4, group 18

Between 1960 and 1983 the metre was defined as 1,650,763.73 wavelengths of a particular orange-red line in the spectrum of krypton-86, which made this obscure gas the international standard of length for 23 years until lasers made the definition obsolete. Krypton is genuinely inert in ordinary conditions but not absolutely so — krypton difluoride exists, though it has to be made at cryogenic temperatures and falls apart above about −30 °C. It makes up about one part per million of the atmosphere.

## Properties

- **Atomic number:** 36
- **Symbol:** Kr
- **Standard atomic weight:** 83.798 u
- **Category:** Noble gas
- **Group:** 18
- **Period:** 4
- **Block:** p-block
- **Electron configuration:** [Ar] 4s² 3d¹⁰ 4p⁶
- **Electrons per shell:** 2, 8, 18, 8
- **Melting point:** 115.79 K — -157.4 °C — -251.2 °F
- **Boiling point:** 119.93 K — -153.2 °C — -243.8 °F
- **Density:** 0.003733 g/cm³
- **Electronegativity:** 3 (Pauling)
- **Oxidation states:** 0, +2
- **Discovered:** 1898 by William Ramsay and Morris Travers

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
- **Noble gas shorthand:** [Ar] 4s² 3d¹⁰ 4p⁶
- **Shells:** K: 2 · L: 8 · M: 18 · N: 8

## What it is used for

- High-performance window glazing, where it insulates better than argon
- Krypton fluoride excimer lasers in semiconductor lithography
- Photographic flash tubes and some high-intensity lamps
- Krypton-85 as a tracer for leak detection and for detecting plutonium production

## Hazards

- Asphyxiant in confined spaces; denser than air

> Density is the gas at 0 °C and 101.325 kPa.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 34 | Selenium | Se | 78.971 |
| 35 | Bromine | Br | 79.904 |
| 36 | Krypton ← | Kr | 83.798 |
| 37 | Rubidium | Rb | 85.468 |
| 38 | Strontium | Sr | 87.62 |

## Group 18

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Krypton sits in group 18 with helium, neon, argon, xenon, radon, oganesson.

## Common questions

### What is the atomic number of krypton?

36. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for krypton?

Kr.

### What is the electron configuration of krypton?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶, or [Ar] 4s² 3d¹⁰ 4p⁶ in noble-gas shorthand.

### What is the melting point of krypton?

115.79 K — -157.4 °C — -251.2 °F

## Related pages

- [Selenium (Se)](https://atoneplace.net/element/selenium/)
- [Bromine (Br)](https://atoneplace.net/element/bromine/)
- [Rubidium (Rb)](https://atoneplace.net/element/rubidium/)
- [Strontium (Sr)](https://atoneplace.net/element/strontium/)
- [Helium (He)](https://atoneplace.net/element/helium/)
- [Neon (Ne)](https://atoneplace.net/element/neon/)
- [Argon (Ar)](https://atoneplace.net/element/argon/)
- [Xenon (Xe)](https://atoneplace.net/element/xenon/)
- [Radon (Rn)](https://atoneplace.net/element/radon/)
- [Oganesson (Og)](https://atoneplace.net/element/oganesson/)

## Sources

- Official vendor product documentation — At One Place (/about/)