Iodine (I)
Iodine is element 53, a halogen in group 17, period 5. A neutral atom has 53 protons, 74 neutrons and 53 electrons, 7 of them valence electrons.
Halogen- Atomic number
- 53
- Atomic mass
- 126.9 u
- Valence electrons
- 7
- Protons · neutrons
- 53 · 74
- Electrons per shell
- 2, 8, 18, 18, 7
- At room temperature
- solid
Bohr model of iodine
The Bohr model draws iodine as a nucleus of 53 protons and 74 neutrons, with its 53 electrons on 5 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 18 in shell 4, 7 in shell 5. Press Build the atom to watch the shells fill from the inside out. The outer ring (the O 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 iodine
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁵
Short form (noble gas notation): [Kr] 5s² 4d¹⁰ 5p⁵. The [Kr] stands for the electrons of krypton, the noble gas before it.
How many valence electrons does iodine have?
Iodine has 7 valence electrons.
Iodine 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 | 53 | equal to the atomic number |
|---|---|---|
| Electrons | 53 | equal to the protons in a neutral atom |
| Neutrons | 74 | mass number 127 − 53 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.
Iodine properties
| Symbol | I |
|---|---|
| Category | Halogen |
| Group · period · block | 17 · 5 · p |
| Atomic mass | 126.9 u |
| State at 25 °C | solid |
| Melting point | 386.9 K (114 °C, 237 °F) |
| Boiling point | 457.6 K (184 °C, 364 °F) |
| Density | 4.93 g/cm³ |
| Electronegativity (Pauling) | 2.66 |
| Atomic radius | 198 pm |
| First ionization energy | 10.451 eV |
| Electron affinity | 3.059 eV |
| Oxidation states | +7, +5, +1, −1 |
| Common ion charge | −1 |
| Discovered | 1811 by Bernard Courtois |
Where iodine sits on the periodic table
Group 17: Fluorine, Chlorine, Bromine, Astatine, Tennessine.
Questions about iodine
How many valence electrons does iodine have?
Iodine has 7 valence electrons.
How many protons, neutrons and electrons does iodine have?
A neutral iodine atom has 53 protons and 53 electrons. Its most common form has about 74 neutrons (mass number 127 − 53 protons).
What is the electron configuration of iodine?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁵, written in short form as [Kr] 5s² 4d¹⁰ 5p⁵.
What does the Bohr model of iodine look like?
A nucleus of 53 protons and 74 neutrons, circled by 5 electron shells holding 2, 8, 18, 18, 7 electrons.
What is the atomic number of iodine?
53. The atomic number is the number of protons in the nucleus, and it is what makes an atom iodine.