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Astatine (At)

Element 85 · halogen · group 17, period 6

Astatine shell diagram: 2, 8, 18, 32, 18, 7 electronsAt85
Electron shells, 2 + 8 + 18 + 32 + 18 + 7. The outer shell is highlighted - it is the only one that takes part in bonding.

Astatine is element 85, a halogen in group 17 and period 6. Its electron configuration is [Xe] 4f14 5d10 6s2 6p5. That leaves 7 valence electrons in the outer shell, with the shells filling 2, 8, 18, 32, 18, 7. It is 1 electron short of a full octet, so it gains them and carries a charge of -1.

Properties

Atomic number85
SymbolAt
Standard atomic weight210 u
Group17
Period6
Blockp-block
Categoryhalogen
Electron configuration1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5
Noble-gas notation[Xe] 4f14 5d10 6s2 6p5
Electrons per shell2, 8, 18, 32, 18, 7
Valence electrons7
Common ionic charge-1
Electronegativity (Pauling)2.2
Protons / electrons85 / 85

Electron configuration of astatine

Orbitals fill from the lowest energy upward. Writing that out for astatine gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5 in plain text.

Everything up to Xe is the same as in that noble gas, so it is usually abbreviated to [Xe] 4f14 5d10 6s2 6p5. The part outside the bracket is what does the chemistry.

SubshellElectronsCapacity
1s 2 2
2s 2 2
2p 6 6
3s 2 2
3p 6 6
3d 10 10
4s 2 2
4p 6 6
4d 10 10
4f 14 14
5s 2 2
5p 6 6
5d 10 10
6s 2 2
6p 5 6

Astatine ion charge

Astatine commonly forms ions with a charge of -1.

It has 7 valence electrons, so it is 1 short of a full octet and 7 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.

Common questions

How many valence electrons does astatine have?

Astatine has 7 valence electrons. For a main-group element the count is the group number minus 10, and astatine is in group 17.

What is the electron configuration of astatine?

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5, or [Xe] 4f14 5d10 6s2 6p5 written from the previous noble gas. Orbitals fill lowest energy first.

What is the charge of astatine?

Astatine commonly forms ions with a charge of -1. With 7 valence electrons it is 1 short of an octet and 7 above an empty shell, so it takes whichever route is shorter.

How many protons, electrons and neutrons does astatine have?

A neutral astatine atom has 85 protons and 85 electrons. Its standard atomic weight is 210, so the most common isotope has about 125 neutrons.

See the ionic charge of every element →

How this page was produced. The configuration was built by filling orbitals in energy order from atomic number 85 alone, not looked up. The shell counts, the valence count and the charge all follow from it. Nothing on this page is written per element.