Connecting Chemistry


Atomic symbol: I
Atomic number: 53
Atomic mass: 126.9

Appearance: Purple black solid at 25°C

Group: 17
Period: 5
Series: Reactive nonmetals
Block: p
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁵

Of all the halogens, iodine is the weakest oxidizing agent and the least electronegative; with respect to all the elements of the Periodic Table, iodine is still a strong oxidizing agent and is fairly electronegative.

Aqueous iodine is used to test for starch. Light orange-brown potassium iodide turns dark blue in the presence of starch.

Fun Fact! Iodine is essential to human life, used in metabolic processes like the healthy functioning of the thyroid, as well as in the prevention of birth defects. Sources of iodine in our diet include seafood, fish, eggs and dairy products and iodized salt.