Iodine is element number 53, with the symbol I. Its name comes from the Greek word for “violet.”
Atomic number 53126.9
IIodineヨウ素 (yōso)
Symbol
I
Atomic weight
126.9
Place in the table
Period 5 · Group 17
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
A violet gas
Iodine was discovered in 1811 and named because its vapor is violet.
Iodine and the body
70–80% of the iodine in the body is in the thyroid gland, where it is used to make thyroid hormones. These hormones are involved in growth and in how the body uses energy.
Iodine is in the fifth row of Group 17, with fluorine, chlorine and bromine.
Think about it
Q1If you saw a violet gas, what would you name it?
Q2Where in the body is the thyroid gland?
Q3Can you name the Group 17 elements and say what their names come from?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — The Group 17 names come from color and smell: chlorine “yellow-green,” bromine “stench,” iodine “violet.”