There is a lot of confusion surrounding the relationship between the terms “fluoride” and “fluorine” on both sides of the forced-fluoridation issue. As the title says, fluoride (F–) is the ionic form of fluorine (F). Similarly, nitride (N3-) is the ionic form of nitrogen (N), iodide (I–) is the ionic form of iodine (I), arsenic ions (As3-, As3+, or As5+) are an ionic form of arsenic (As, which has more than one ionic form), and radium ions (Ra2+) are the ionic form of radium (Ra), for example. Fluorine, nitrogen, iodine, arsenic, and radium are all chemical elements, a full list of which can be found in the periodic table. Every atom, including every atom which is also an ion and regardless of whether or not the atom is part of a chemical compound, is an atom of some particular chemical element. The characteristic which distinguishes an atom of one element from that of another element is the number of protons in the nucleus of the atom. That number is called the atomic number. The atomic numbers of fluorine, nitrogen, iodine, arsenic, and radium are 9, 7, 53, 33, and 88, respectively. Again, the atomic numbers of all of the chemical elements can be found in the periodic table. Every fluorine atom has 9 protons in its nucleus and every atom with 9 protons in its nucleus is a fluorine atom, every nitrogen atom has 7 protons in its nucleus and every atom with 7 protons in its nucleus is a nitrogen atom, and the pattern is the same for all of the other elements.
A fluoride ion is an atom with 9 protons in its nucleus, making it a fluorine atom. It is an “ion” because the number of electrons is not equal to the number of protons, which is also the reason for the “ide” suffix. More specifically, each fluoride ion (or anion to be more precise, because its charge is negative) has 10 electrons, giving it a net electrical charge (also known as a valence) of -1. The negative sign and the magnitude of “1” which make up that “-1” are conventions in chemistry which were adopted for the sake of convenience. The “ide” suffix used for the ionic forms of fluorine, nitrogen, iodine, and other non-metals is also merely a convention, and it could have been decided to use it for metals and metalloids instead, or not at all. For example, the chemical CaF2 is conventionally called calcium fluoride, but if the naming conventions were different it could be referred to as fluorine calcide or calcium fluorine instead. The calcium in calcium fluoride is just as much in its ionic form as the fluorine is, but just happens to not be given its own suffix or prefix or anything else to indicate that fact, and it makes no more sense to say that fluoride ions are not the chemical element fluorine than it does to say that calcium ions are not the chemical element calcium. The ionic nature of the chemical compound calcium fluoride, and of the calcium which forms part of that compound, can be inferred from the presence of the word “fluoride”, with its ion-indicating suffix. Nevertheless, the difference in the naming conventions for metallic and non-metallic ions does appear to be part of the reason for a common misunderstanding.
By now it should be very clear that the terms “fluoride” and “fluorine” are not mutually exclusive. Not only are they not mutually exclusive, but fluoride is fluorine; every fluoride ion is in fact a fluorine atom. The difference between the terms is simply that “fluoride” is more specific, “fluorine” more general. Unfortunately it is commonly claimed that those terms are mutually exclusive, and that the only form of fluorine is fluorine gas. As previously stated, “fluorine” refers to any atom with 9 protons in its nucleus. It is a general term which includes fluoride, fluorine gas, and covalently bound fluorine (such as that found in Teflon, chlorofluorocarbons, many pharmaceutical drugs, and various other chemicals). The term “fluorides” is used for compounds which contain fluorine, regardless of whether the fluorine is ionic or covalently bound, which may be another source of confusion. Desperation to deny harm done by fluoride, and the superficial familiarity (and contempt) which comes from using fluoridated products regularly, are almost certainly additional factors.
Why it matters
So why does this matter? One reason is that chemical elements are not biodegradable, and that includes the ionic forms of elements. The fact that fluoride cannot be broken down by the human body, or any other living organism, has implications for its bioaccumulation and chronic toxicity. (The word “chronic” refers to the duration of exposure, not the severity of the health effects. Chronic exposure is longer term than acute exposure.) Fluorine is not the only toxic, naturally occurring chemical element which accumulates mostly in bone and is not a nutrient – lead being one example. Even the chemical elements which are nutrients, such as iron and calcium, have small margins of safety in comparison with water-soluble vitamins such as vitamin C. Vitamins are chemical compounds, not elements.
Another reason is that legitimate concerns about fluoride toxicity are claimed to be a case of mistaken identity. Those who make such claims appear to think that we do not understand the difference between fluorine gas and fluoride and have incorrectly assumed that fluoride is hazardous just because fluorine gas is hazardous. In reality, they are either deliberately lying about fluoride toxicity or have incorrectly and irrationally assumed that just because fluorine gas and fluoride are not the same thing, fluoride must be more or less harmless. They often liken fluoride to the chloride in table salt, but if they bothered to compare the lethal doses of sodium fluoride and sodium chloride, or to discover other relevant facts, they would know how silly that is. They also claim that fluoride is biologically similar to iodine merely because they are both halogens, which is equally silly. Bromine is another halogen, and that is not biologically similar to iodine either. For that matter, neither is the halogen chlorine, including its ionic form, chloride. You can go through the rest of the naturally occurring chemical elements and the story is the same.
Note also that “fluorine” is sometimes used in place of “fluoride” in the literature, and if you think those terms are mutually exclusive it is bound to create confusion. The former term was actually preferred prior to 1950, or thereabouts. I encountered one fluoridewit who admitted not having read Fluorine Intoxication by Kaj Roholm (1937), but who still insisted the book is not about fluoride.
It is also important that those of us who are pro-choice on taking fluoride get our facts straight, even if the argument against forced-fluoridation does not depend on those particular facts. Fluorine (and consequently its ionic form, fluoride) is a non-metal, not a heavy metal or any other kind of metal. The fluoridation chemicals which are used for forced-fluoridation are industrial grade, and come with contaminants which include heavy metals, but the fluoride itself is not metallic. Additionally, it should be understood that although some ionic fluoride compounds are more hazardous than others, due to differences in bioavailability and possibly other reasons in some cases (e.g. the leaching of lead by silicofluorides), naturally occurring fluoride is not inherently less harmful than fluoride from artificial sources. For example, active volcanoes give off large quantities of hydrogen fluoride (HF) gas, which is highly bioavailable and highly toxic. When you eat or drink, at least some of the fluoride which is ingested forms HF in your stomach acid, regardless of whether it came from an artificial or natural source. The study of what happens to chemicals taken into the body is known as pharmacokinetics.