---
title: "Astatine (At): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/astatine.html
description: "Astatine (At), element 85: atomic mass [210], electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵, group 17, period 6, p-block metalloid. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
85At[210]

# Astatine (At) – element 85

Astatine is a chemical element with the symbol **At** and atomic number **85**. It is a metalloid in group 17 (halogens), period 6 of the periodic table (p-block), and is a solid at room temperature.

Astatine (At) has atomic number 85, atomic mass [210] and electron configuration [Xe] 4f14 5d10 6s2 6p5.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Astatine facts

| Symbol | At |
| --- | --- |
| Atomic number | 85 |
| Atomic mass | [210] |
| Category | metalloid |
| Group | group 17 (halogens) |
| Period | 6 |
| Block | p-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5 |
| Noble-gas notation | [Xe] 4f14 5d10 6s2 6p5 |
| Electrons per shell | 2, 8, 18, 32, 18, 7 |
| Valence electrons | 7 |

## Bohr model and shells

Astatine has 85 electrons in 6 shells: 2, 8, 18, 32, 18, 7. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 575 K (301.9 °C) |
| --- | --- |
| Boiling point | 610 K (336.9 °C) |
| Density | 6.35 g/cm³ |
| Electronegativity (Pauling) | 2.2 |
| Electron affinity | 233 kJ/mol |
| Ionization energies | 899.003 kJ/mol (1st) |
| Discovered by | Dale R. Corson |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing At.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of astatine?

The atomic mass of astatine is [210] (mass number of its longest-lived isotope, since it has no stable isotope).

### What is the electron configuration of astatine?

Astatine has 85 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁵, or [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ in noble-gas notation. Electrons per shell: 2, 8, 18, 32, 18, 7.

### How many valence electrons does astatine have?

Astatine has 7 valence electrons (group 17).

### Is astatine a metal?

Astatine is a metalloid: it has properties between metals and nonmetals.

### Where is astatine on the periodic table?

Astatine is in group 17 (halogens), period 6, in the p-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.