Astatine (At)

Astatine properties

Atomic number

85

Atomic mass

210 u

Category

Halogen

Group

17

Period

6

Block

p-block

State at room temp.

Solid

Electronegativity

2.2

Melting point

575 K (301.8 °C)

Boiling point

610 K (336.8 °C)

Density

7 g/cm³

Valence electrons

7

Common charges

−1

Oxidation states

+7, +5, +3, +1, −1

Atomic radius

202 pm

Ionization energy

9.5 eV

Electron affinity

2.8 eV

Radioactive

Yes, no stable isotopes

Discovered

1940

Astatine electron configuration

The electron configuration of Astatine (At) is [Xe] 4f14 5d10 6s2 6p5. Its 85 electrons are arranged in shells as 2, 8, 18, 32, 18, 7.

Protons, neutrons and electrons in Astatine

A neutral Astatine atom has 85 protons and 85 electrons. Most Astatine atoms have about 125 neutrons: the atomic mass rounded to 210, minus the atomic number 85.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Astatine have?

7

Astatine has 7 valence electrons in its outermost shell, shell 6. These are the electrons involved in chemical bonding.

See every element: Periodic table with valence electrons

Astatine orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Astatine

210 g/mol

One mole of Astatine atoms (6.022 × 10²³ atoms) has a mass of 210 grams. Use this value to convert between grams and moles.

Astatine facts

• Astatine is the rarest naturally occurring element in Earth's crust; only a tiny trace exists at any moment, formed by the decay of heavier elements.
• No one has ever seen a visible piece of astatine, because any sizable sample would be vaporized by the heat of its own radioactivity.
• Astatine (At) has atomic number 85 and is a solid at room temperature. It was discovered in 1940.

Position in the periodic table

Astatine is element 85, in period 6 and group 17 of the periodic table, in the p-block.

All halogens

Uses of Astatine

Astatine has no commercial uses because it is extremely rare and all of its isotopes are short-lived. Its isotope astatine-211, which has a half-life of about 7 hours, is being studied for targeted alpha therapy. In this cancer treatment, astatine is attached to molecules that seek out tumor cells and destroy them with alpha radiation that travels only a very short distance.

Who discovered Astatine?

Dale Corson, Kenneth MacKenzie and Emilio Segrè first made astatine in 1940 at the University of California, Berkeley, by bombarding bismuth with alpha particles. Its name comes from the Greek astatos, meaning 'unstable'.

Where does the name come from?

Astatine comes from the Greek astatos, meaning 'unstable'. The scientists who first made it in 1940 chose the name because every form of the element is radioactive and decays quickly.

Discovery timeline