The difference between fluorine and fluoride is that the former is an element and the latter a generic term applied to compounds of this element, or sometimes more specifically the fluoride ion, F-. At room temperature and normal atmospheric pressure, fluorine is a pale yellow gas and belongs to a group of elements known as the halogens, which also contains chlorine, bromine, iodine and astatine. It is the most electronegative, and most reactive, of all the elements. Fluorine always forms compounds by accepting an electron from another atom and in its compounds always has an oxidation number of -1. These compounds are known as fluorides, and may be ionic, for example sodium fluoride (Na+F-) or covalent, for example sulfur hexafluoride (SF6).
Fluorine and fluoride differ most markedly in that elemental fluorine is extremely reactive, whereas fluorides are usually very stable and relatively unreactive. This is because fluorine tends to bond very strongly with atoms of other elements. Chemical reactions involving a fluoride generally result in the formation of another fluoride. In aqueous solution as hydrofluoric acid, for example, hydrogen fluoride will react with many metals to form metal fluorides. Fluorine is particularly attracted to the element calcium, so metal fluorides will often react with calcium compounds to form calcium fluoride or other substances with a calcium-fluorine bond.
This element is not found naturally on Earth in its uncombined state, but is common in the Earth’s crust in the form of fluoride minerals, such as fluorite or calcium fluoride (CaF2). In the human body, fluoride reacts with a form of calcium phosphate called hydroxyapatite in the bones and teeth to form fluoroapatite, which also occurs as a mineral. In the right amount, this appears to have a strengthening effect and provides significant protection against tooth decay and dental cavities. Despite its presence in the human body and its beneficial effects at the right levels, fluorine is not considered an essential element as humans appear able to live without it, and too much fluoride can be harmful.
Due to its beneficial effects on teeth, fluoride is often added to dental products such as toothpaste and mouthwashes, in the soluble forms of sodium fluoride or sodium monofluorophosphate. In some areas, it is also added to public drinking water supplies for the same reason. This has caused controversy, not only due to the potential harmful effects of excessive fluoride. Opponents of fluoridation of water supplies have argued that it is a form of enforced medication, while those in favor argue that it simply brings fluoride levels up to normal for areas that are deficient in this element.
Although elemental fluorine is highly toxic due to its reactivity, fluorides are generally less so. Nevertheless, ingestion of soluble metal fluorides in other than very small amounts can have serious toxic effects and for this reason, toothpaste and mouthwash should not be swallowed. The acute effects of fluoride ingestion include damage to the brain and kidneys and effects on the heart. The lethal dose for sodium fluoride is estimated at 0.175 – 0.353 ounces (5-10 grams), an amount very unlikely to be absorbed through contact with generally available products containing fluoride. The effects of chronic overexposure to fluoride include mottling of teeth, brittle bones, anemia and stiff joints.
Fluorine and fluoride are widely used in industry. One very useful fluorine-containing product is polytetrafluoroethylene (PTFE), a fluorinated plastic sold under a well-known trade name and used domestically on cooking utensils because of its heat resistance and non-stick properties. In addition, PTFE is used industrially for the storage of reactive substances, due to its chemical inertness. Fluorine and fluoride are also used in the production of pesticides, such as sulfuryl fluoride, and in an intermediate step in the enrichment of uranium for nuclear reactors.