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
by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated October 05, 2017

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.