---
title: "Radon (Rn) — element 86"
description: "Radon is element 86, symbol Rn, most stable isotope 222. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/radon/
site: "At One Place"
---

# Radon (Rn)

**Radon — element 86: Rn**

[222] · Noble gas · period 6, group 18

Radon is the second leading cause of lung cancer after smoking, and the exposure happens at home: uranium in the ground decays to radium and then to radon, an inert gas that seeps up through foundations and accumulates in basements. Because it is chemically inert it is breathed in and out freely, but its decay products are solid and stick to lung tissue. Testing a house costs very little and remediation is usually a fan and a pipe, which makes it one of the more tractable environmental health risks there is.

## Properties

- **Atomic number:** 86
- **Symbol:** Rn
- **Mass number of most stable isotope:** [222]
- **Category:** Noble gas
- **Group:** 18
- **Period:** 6
- **Block:** p-block
- **Electron configuration:** [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁶
- **Electrons per shell:** 2, 8, 18, 32, 18, 8
- **Melting point:** 202 K — -71.1 °C — -96.1 °F
- **Boiling point:** 211.45 K — -61.7 °C — -79.1 °F
- **Density:** 0.00973 g/cm³
- **Oxidation states:** 0
- **Discovered:** 1900 by Friedrich Ernst Dorn

## Electron configuration

- **Full:** 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶
- **Noble gas shorthand:** [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁶
- **Shells:** K: 2 · L: 8 · M: 18 · N: 32 · O: 18 · P: 8

## What it is used for

- Historically sealed in needles for cancer radiotherapy
- A tracer for studying air movement and for earthquake prediction research

## Hazards

- The leading cause of lung cancer in non-smokers
- Colourless, odourless and eight times denser than air, so it collects in basements
- Risk depends entirely on local geology; neighbouring houses can differ

> No stable isotope; the mass given is the mass number of radon-222, the longest-lived at 3.82 days. Density is the gas at 0 °C and 101.325 kPa, which makes radon the densest gas at room conditions.

## Neighbours in the table

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 84 | Polonium | Po | [209] |
| 85 | Astatine | At | [210] |
| 86 | Radon ← | Rn | [222] |
| 87 | Francium | Fr | [223] |
| 88 | Radium | Ra | [226] |

## Group 18

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

## Common questions

### What is the atomic number of radon?

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

### What is the symbol for radon?

Rn.

### What is the electron configuration of radon?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶, or [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁶ in noble-gas shorthand.

### What is the melting point of radon?

202 K — -71.1 °C — -96.1 °F

## Related pages

- [Polonium (Po)](https://atoneplace.net/element/polonium/)
- [Astatine (At)](https://atoneplace.net/element/astatine/)
- [Francium (Fr)](https://atoneplace.net/element/francium/)
- [Radium (Ra)](https://atoneplace.net/element/radium/)
- [Helium (He)](https://atoneplace.net/element/helium/)
- [Neon (Ne)](https://atoneplace.net/element/neon/)
- [Argon (Ar)](https://atoneplace.net/element/argon/)
- [Krypton (Kr)](https://atoneplace.net/element/krypton/)
- [Xenon (Xe)](https://atoneplace.net/element/xenon/)
- [Oganesson (Og)](https://atoneplace.net/element/oganesson/)

## Sources

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