Astatine (At)
Astatine is element 85, a halogen in group 17, period 6. A neutral atom has 85 protons, 125 neutrons and 85 electrons, 7 of them valence electrons.
Halogen- Atomic number
- 85
- Atomic mass
- 209.99 u
- Valence electrons
- 7
- Protons · neutrons
- 85 · 125
- Electrons per shell
- 2, 8, 18, 32, 18, 7
- At room temperature
- solid
Bohr model of astatine
The Bohr model draws astatine as a nucleus of 85 protons and 125 neutrons, with its 85 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 32 in shell 4, 18 in shell 5, 7 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of astatine
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁵
Short form (noble gas notation): [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁵. The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does astatine have?
Astatine has 7 valence electrons.
Astatine is in group 17, and for groups 13–18 you subtract 10 from the group number: 17 − 10 = 7. It tends to gain 1 electron to complete an octet, forming a −1 ion.
Protons, neutrons and electrons
| Protons | 85 | equal to the atomic number |
|---|---|---|
| Electrons | 85 | equal to the protons in a neutral atom |
| Neutrons | 125 | mass number 210 − 85 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Astatine properties
| Symbol | At |
|---|---|
| Category | Halogen |
| Group · period · block | 17 · 6 · p |
| Atomic mass | 209.99 u |
| State at 25 °C | solid |
| Melting point | 575 K (302 °C, 575 °F) |
| Boiling point | — |
| Density | 7 g/cm³ |
| Electronegativity (Pauling) | 2.2 |
| Atomic radius | 202 pm |
| First ionization energy | 9.5 eV |
| Electron affinity | 2.8 eV |
| Oxidation states | 7, 5, 3, 1, −1 |
| Common ion charge | −1 |
| Discovered | 1940 by Dale R. Corson |
Where astatine sits on the periodic table
Group 17: Fluorine, Chlorine, Bromine, Iodine, Tennessine.
Questions about astatine
How many valence electrons does astatine have?
Astatine has 7 valence electrons.
How many protons, neutrons and electrons does astatine have?
A neutral astatine atom has 85 protons and 85 electrons. Its most common form has about 125 neutrons (mass number 210 − 85 protons).
What is the electron configuration of astatine?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁵, written in short form as [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p⁵.
What does the Bohr model of astatine look like?
A nucleus of 85 protons and 125 neutrons, circled by 6 electron shells holding 2, 8, 18, 32, 18, 7 electrons.
What is the atomic number of astatine?
85. The atomic number is the number of protons in the nucleus, and it is what makes an atom astatine.