Iodine (I)
Element 53 · halogen · group 17, period 5
Iodine is element 53, a halogen in group 17 and period 5. Its electron configuration is [Kr] 4d10 5s2 5p5. That leaves 7 valence electrons in the outer shell, with the shells filling 2, 8, 18, 18, 7. It is 1 electron short of a full octet, so it gains them and carries a charge of -1.
- 53 protons
- 7 valence e−
- -1
- p-block
Properties
| Atomic number | 53 |
|---|---|
| Symbol | I |
| Standard atomic weight | 126.9 u |
| Group | 17 |
| Period | 5 |
| Block | p-block |
| Category | halogen |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5 |
| Noble-gas notation | [Kr] 4d10 5s2 5p5 |
| Electrons per shell | 2, 8, 18, 18, 7 |
| Valence electrons | 7 |
| Common ionic charge | -1 |
| Electronegativity (Pauling) | 2.66 |
| Protons / electrons | 53 / 53 |
Electron configuration of iodine
Orbitals fill from the lowest energy upward. Writing that out for iodine gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5 in plain text.
Everything up to Kr is the same as in that noble gas, so it is usually abbreviated to [Kr] 4d10 5s2 5p5. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 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 |
| 5s | 2 | 2 |
| 5p | 5 | 6 |
Iodine ion charge
Iodine 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 iodine have?
Iodine has 7 valence electrons. For a main-group element the count is the group number minus 10, and iodine is in group 17.
What is the electron configuration of iodine?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5, or [Kr] 4d10 5s2 5p5 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of iodine?
Iodine 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 iodine have?
A neutral iodine atom has 53 protons and 53 electrons. Its standard atomic weight is 126.9, so the most common isotope has about 74 neutrons.
Nearby elements
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