What Is the Difference Between Fluorine and Fluoride?

Toothpaste contains fluoride, but not free fluorine.
Toothpaste contains fluoride, but not free fluorine. Westend61 / Getty Images

First off, yes, it's fluorine and fluoride and not flourine and flouride. The mis-spelling is common, but the 'u' comes before the 'o'. Fluorine is a chemical element. In pure form, it is a highly toxic, reactive, yellowish-green gas. The fluorine anion, F-, or any of the compounds containing the anion are termed fluorides. When you hear about fluoride in drinking water, it comes from adding a fluorine compound (usually sodium fluoride, sodium fluorosilicate, or fluorosilicic acid) to drinking water, which dissociates to release the F- ion. Stable fluorides are also found in fluoridated toothpaste and mouthwash.

Summary of the Difference

Fluorine is an element. Fluoride either refers to the fluorine ion or to a compound that contains the element fluorine.