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Properties of Matter Element Card 8, Lesson 21



Melting point

113.5° C

Boiling point

184.4° C


4.9 g/cm³



Other physical properties

Solid iodine slowly releases violet iodine gas at room temperature.

Chemical properties

Iodine reacts readily with metals to form iodides.


One compound of iodine is potassium iodide, a white solid.


In the human body, iodine is used to make the hormone thyroxin. In the form of potassium iodide, it is added to salt to prevent goiter. Iodine kills microorganisms and is used to make antiseptics.


Iodine is found in seawater. Iodine is concentrated in the tissues of seaweed. To obtain iodine, people extract it from harvested seaweed.

Violet Iodine gas in a test tube

Although iodine is a black-violet solid at room temperature, it turns into a violet gas when heated above 185 ° C.


Iodine is an essential part of our diet. Lack of this element causes large goiters like this. (A goiter is a swelling of the thyroid gland.) The comound potassium iodide is added to table salt to prevent this problem.

A woman with a large goiter swelling out of her neck
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