Element 53 · Iodine (I)

Iodine Bohr model: diagram and electrons per shell

The iodine Bohr model shows a iodine atom (I) as a small nucleus with its electrons circling it in 5 shells: 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O. This page has a rotating 3D iodine Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the iodine Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of iodine (I), a simplified picture of a single iodine atom. Its nucleus holds 53 protons, and a neutral iodine atom has 53 electrons, arranged around it in 5 shells (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O).

I K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 184s² 4p⁶ 4d¹⁰ O · 75s² 5p⁵

Iodine Bohr model diagram

Bohr model diagram of iodine: a nucleus of 53 protons with 53 electrons on 5 shells, 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O, each ring labelled with its shell letter. — The iodine Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O).

Iodine electrons per shell

A neutral iodine atom has 53 electrons, one for each of its 53 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O.

Electrons in each shell of the iodine Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	18	18	3s² 3p⁶ 3d¹⁰
N	4	18	32	4s² 4p⁶ 4d¹⁰
O	5	7	50	5s² 5p⁵

How the iodine Bohr model builds up, shell by shell

Watch the iodine Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O) as it forms.

Animation of the iodine Bohr model being built: a nucleus of 53 protons appears first, then each shell grows in around it and takes its electrons, giving 53 electrons on 5 shells (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O). — The iodine Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O. Protons are red, neutrons yellow and electrons blue.

How to draw the iodine Bohr model

Find the atomic number. Iodine has atomic number 53, so a neutral atom has 53 protons and 53 electrons.
Draw the nucleus. Put a circle in the centre and write I in it. The 53 protons sit there with the neutrons.
Draw the shells. Sketch 5 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N and 7 in shell O.
Check the total. 2 + 8 + 18 + 18 + 7 = 53, the atomic number, so every electron is accounted for.

Atomic data for the iodine Bohr model

The numbers behind the iodine Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol: I
Atomic number: 53
Atomic mass: 126.9045 u
Family: Halogens
Position: group 17, period 5
Block: p-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁵
Shorthand: [Kr] 4d¹⁰ 5s² 5p⁵
Electrons per shell: 2, 8, 18, 18, 7
Outer-shell electrons: 7 in shell O

Ionisation energies

I₁: 1008.4
I₂: 1845.9
I₃: 3180

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Calculated (pm): 115
Empirical (pm): 140
Covalent (pm): 133
Van der Waals (pm): 198

Electronegativity and electron affinity

Electronegativity (Pauling): 2.66
Electron affinity (kJ/mol): 295.153

Oxidation states

−1 +1 +3 +5 +7

Charges the element commonly takes in compounds.

Physical properties, abundance and history of iodine

Bulk properties of iodine, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions: Solid
Appearance: Lustrous metallic gray, violet as a gas
Melting point: 113.7°C (386.85 K)
Boiling point: 184.25°C (457.4 K)
Density: 4.933 g/cm³
Specific heat (J/g·K): 0.214
Heat of fusion (kJ/mol): 15.52
Heat of vaporisation (kJ/mol): 41.95

Abundance

Earth's crust (mg/kg): 0.45
Oceans (mg/L): 0.06

Discovery

Discovered by: Bernard Courtois
Year: 1811

Common compounds

3-Iodo-2-propynyl butylcarbamate C8H12INO2
Clioquinol C9H5ClINO
Idoxuridine C9H11IN2O5
Potassium Iodide IK
Iodofenphos C8H8Cl2IO3PS
Hydrogen iodide HI
Trametinib C26H23FIN5O4
Flubendiamide C23H22F7IN2O4S

Compounds listed in the PubChem database.

Main isotopes of iodine

Isotopes of iodine share the same 53 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of iodine: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
124	–	4.176 d	β⁺
125	–	59.392 d	EC
126	–	12.93 d	β⁺, β⁻
127	100 %	stable	–
129	–	16.14 My	β⁻
131	–	8.025 d	β⁻

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

More about iodine

Iodine on the periodic table – properties, isotopes, uses and the full iodine page.
Halogens – all halogen elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.