Fluorine, Fluorides, & Chemical Nomenclature

Although dentists have long known that fluorine is essential for healthy teeth, members of the public, when writing letters to newspapers, sometimes fail to distinguish between elements and compounds. A few definitions and points of chemical terminology may therefore be helpful.

Should you wish to go straight to crystal structure click on apatite, or click on a modern evaluation for the first two paragraphs of Tim White et al's Apatite – An Adaptive Framework Structure, to be published (2005) in "Reviews in Mineralogy and Geochemistry" (formerly "Reviews in Mineralogy").

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If you already know all about atoms & ions and when to use the suffixes -ide & -ate, you may wish to jump straight to Fluorine.

Note that many of the links on this page are to external sources! Some of these may have been changed.

Element:

An element is the smallest part of a substance that cannot be resolved by chemical means into simpler substances. [Chambers]

Atom:

The smallest unit of an element, having all the characteristics of that element and consisting of a dense, central, positively charged nucleus surrounded by a system of electrons. The entire structure has an approximate diameter of 10-8 centimeter and characteristically remains undivided in chemical reactions except for limited removal, transfer, or exchange of certain electrons. [AHD]

Atomic nucleus:

An atom's nucleus is constructed of protons and neutrons. Protons have an electrical charge of +1. Neutrons are neutral; i.e. they have a charge of 0.

Electrons:

Because electrons have a charge of -1, an electrically neutral atom has equal numbers of electrons and protons.

Element – an alternative definition:

An element is composed of atoms with an identical number of protons in each nucleus. Elements cannot be reduced to simpler substances by normal chemical means.

Ion:

An ion is an atom, or a group of atoms, that has acquired a net electric charge by gaining or losing one or more electrons [AHD]. As a proton and an electron have equal but opposite charges, ions always have a whole number of unit charges. An ion with a net positive charge is called a cation; an ion with a net negative charge is called an anion. [Columbia]

The architecture of ionic crystals. This external link is included with the kind permission of Professor Jack M. Rice, Geology Dept., Oregon State University.

Atomic Number:

An element's atomic number is the number of protons in the nucleus of an atom of that element. This also equals the number of electrons in the neutral atom.

Periodic Table:

The Periodic Table orders elements according to their atomic number in such a way that those with related properties are in the same column; e.g. the chemically-related non-metallic elements fluorine, chlorine, bromine, and iodine (the halogens – literally "salt producers") form a column.

Display an excellent copyright version of the Periodic Table of the Elements. This is an external link.

Copyright Notice: "You do not need permission to make links to WebElements TM.   Please set all links to WebElements TM to http://www.webelements.com/.    WebElements TM is under development, and only that URL is guaranteed.
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Another display – courtesy of EnvironmentalChemistry.com: Periodic Table of Elements   This is an external link.

An external link to a more technical account of Atoms, Ions, & Bonds is included with kind permission of Professor Jack M. Rice, Geology Dept., Oregon State University.

The composition of the Earth’s crust:

Although there are 92 elements in nature, eight make more than 98% of the Earth’s crust. By volume, Oxygen alone accounts for 94% of the crust (47% by weight), more than 20% by volume of the atmosphere, and 89% by weight of water.

J.E. Lovelock pointed out that "It would require only an increase of about 4% in the atmospheric level of oxygen to bring the world into danger of conflagration. At 25% oxygen level even damp vegetation will continue to burn once combustion has started, so that a forest fire started by a lightning flash would burn fiercely till all combustible material was consumed." (J.E. Lovelock: Gaia, A New Look at Life on Earth, 1979, p.38)

Silicon makes up 28% of the crust, so that O and Si together account for nearly 75% of the crust. Aluminum contributes 8%, Iron 5%; Calcium, Sodium, Potassium,and Magnesium together make up about 7.5%, The remaining 84 natural elements together contribute only 1.5%

Compounds:  -ide  and  -ate

Oxygen is very reactive, readily combining with many of the other elements; e.g. the oxides H2O, CO2, SiO2 (quartz), Al2O3 (corundum), FeO, Fe2O3 (rust), CaO (quicklime), and MgO. In each case Oxygen is an anion whose charge of -2 is balanced by a (positively charged) cation.

By analogy with oxides chemists refer to chlorides & fluorides (i.e. halides), and sulfides (or sulphides).

Radical:

"An atom or a group of atoms with at least one unpaired electron" [AHD] – Note that this definition doesn't distinguish between radical and ion".

"A group of atoms joined together in some particular spatial structure and that take part in most chemical reactions as a single unit. ... The use of these radicals simplifies the naming and description of inorganic compounds, since such usage does not consider the electronic charge on the group." [Columbia]

Examples are:  (NH4)    (CO 3)    (SO4)    (SiO 4)    (PO4)

Group:

"Two or more atoms behaving or regarded as behaving as a single chemical unit" [AHD]; e.g. the phosphate group  (PO4)

The terms radical and group are near synonyms. Radical is used in describing organic molecules, where electric charge is important; whereas group is preferred in the description of crystal structures – as in the accompanying paper on the crystal structure of fluor-apatite.

Historical Note:

The pioneer chemist Antoine Lavoisier (1743-1794) concluded that organic compounds were oxides of compound radicals and therefore contained at least the three elements, C, H, O. This conclusion was accepted by the great Swedish chemist Berzelius (1779-1848). In an influential textbook published in 1817, Leopold Gmelin (1788-1853) classified inorganic compounds as binary – composed of two elements – whereas organic compounds were ternary – containing at least three elements, C, H and O. [EB 1929]

Oxides were recognised as the type binary compounds – the suffix "ide" being derived from the word acid; e.g. FeO, H2O, CO2, CaO, MgO, and CO2

Gay-Lussac (1778-1853) showed that the cyanogen group (CN) remained unchanged throughout a number of compounds – such as cyanogen bromide (CN)Br or Br(CN), cyanogen chloride (CN)Cl or Cl(CN), and the gas carbon nitride (C2N2). As a consequence of these discoveries, numerous attempts were made to find other radicals which would function like elements.

This explains the origin of the suffixes -ide (for binary compounds) and -ate (for compounds with a radical containing two or more elements). Thus CaO is "calcium oxide" while Ca(CO3) is "calcium carbonate"; CaF2 is "calcium fluoride" while Ca5F(PO4)3 is "calcium fluorine phosphate".

Atoms can attain a more stable arrangement of electrons in their outermost shell by interacting with one another. An ionic bond is formed when electrons are transferred from one atom to the other. A covalent bond is formed when electrons are shared between atoms.

In simple minerals such as NaCl and KCl bonding is ionic, but bonding between the atoms in radicals such as (CO3),  (SO4), and  (PO4) is the tighter, co-valent form.

I am grateful to Professor Randolph S. Duran, Chemistry Dept, University of Florida, for permission to include this external link to a helpful explanation of covalent & ionic bonds.

Another excellent external link is provided by The National Health Museum on condition that it is not included within a frame. To view this link, copy it to your browser's address toolbar and click on Go:

http://www.accessexcellence.org/AB/GG/cov_IonicBs.html

Salt (NaCl) as an ionic compound

Common salt is a compound of equal numbers of (positive) Na cations and (negative) Cl anions.
The Na+ and Cl  ions alternate along the rows and columns of the cubic structure, but when salt is in solution the ions are freed from these orderly constraints.
Recall how the suffix -ide was introduced for certain compounds, and note that no advantage comes from renaming the chlorine ion the chloride ion.

Fluorine – atom & ion

Fluorine is a highly reactive relative of chlorine. Fluorine combines with hydrogen to form HF (hydrogen fluoride or hydrofluoric acid) which etches glass and quartz. Combined with oxygen, fluorine forms F2O, which is properly named either fluorine oxide or oxygen fluoride. Just as the salts of hydrochloric acid are chlorides, so the salts of hydrofluoric acid are fluorides.

In recent years the term fluoride has unfortunately become debased. It is now commonly used for the fluorine ion and for almost any compound containing fluorine.

Fluorine is a very minor constitutent of the Earth’s crust. It gets its name from the beautiful mineral fluorspar (fluorite), which is a true fluoride (CaF2). Fluorspar occurs in veins, often associated with galena (lead sulfide – PbS). The mineral is an important flux, and hence its name (Latin: fluere to flow). The phenomenon of fluorescence also derives its name from this mineral – light of one wavelength is absorbed while light at a longer wavelength is emitted.

Crystal structure of Fluorite. This external link is included with kind permission of Professor Randolph S. Duran, Davidson College Chemistry Dept, NC. If the diagrams are not displayed following the text, try searching Google for the two words: Fluorite Davidson, then click on Crystal Structure of Fluorite. Note that the images can be rotated! Unfortunately these interesting images can't always displayed.]

Other fluorine-bearing minerals are:

Beginning in 1930 fluorine was intensively used for the manufacture of the refrigerant Freon (CCl 2F2 and other ChloroFluorCarbons). These CPCs were popular because they are non-toxic and nonflammable. As they do not normally react with other substances, they are ideally suited as sprays. Although safe for a person to inhale, CPCs are known to damage the earth’s ozone layer – a shield that protects the Earth against harmful radiation. The use of CPCs for refrigerants was abandoned in 1995 when the affect on Earth’s ozone layer was recognised. Fluorine continues, however, to be used in many industrial products, such as Teflon.

The inorganic material of teeth and bones is apatite, and because the univalent OH (hydroxyl) group is readily available, hydroxy-apatite is formed. The structure permits fluorine ions to replace hyroxyl without disrupting the crystal architecture, and the resulting fluor-apatite is more stable and resistant to bacteriological attack.

Healthy teeth and bones require both phosphorus and fluorine. How do our bodies get these rare elements? Apatite normally occurs in tiny crystals dispersed through common rocks. When the host rocks weather and decay, these crystals are released, and some of the fluorine finds its way in ionic form into our drinking water. If the fluorine content of the water is between 2-5% we can expect to find strong healthy teeth. If the concentration is less than this (0-2%), tooth decay is likely to be common; if the concentration is much more (5-10%), many teeth will be mottled yellow or brown.

It must be emphasised that the properties of compounds bear little relationship to those of their constituent elements. Chlorine was used as a poison gas in the first World War, and sodium reacts violently with water, yet when combined they constitute the common salt used in the kitchen and the dining room. Salt is a product so generally useful that it has been used as currency; hence the word salary.

In some areas, fluoride ion is added to drinking water (in very low concentrations) since it renders tooth enamel relatively immune to bacteriological attack. It does this by replacing the OH group of hydroxyapatite with fluoride. In other areas, fluoride is not added to water, despite the benefits, as a consequence of protests from civil rights activists who object to the addition of anything to water.

Fluoride is the ionic form of fluorine (F), which is widely distributed in nature. Bones and teeth contain most of the body's fluorine. Saltwater fish and tea are rich sources, but the main source is drinking water.

Fluorine is added to city water supplies in the proportion of about one part per million to help prevent tooth decay. Sodium fluoride [NaF], stannous (tin) fluoride [SnF2] and sodium monofluorophosphate (SMFP) [Na2(PO3F)] are fluorine compounds often added to toothpaste to help prevent tooth decay. Note: Each Phosphorous in SMFP has one Oxygen double-bonded, 2 Oxygens single-bonded, and one F.

The following external links are essential reading for anyone interested in fluoridation. They are included by Dr Garfield's kind permission.

Eugene Garfield: Fluoridation, "Texas Teeth," and the Great Conspiracy. Eugene Garfield's Home Page

Eugene Garfield: Fluoridation, "Texas Teeth," and the Great Conspiracy. Part 1. The Issues, Essays of an Information Scientist, Vol.9, p.89, 1986. Current Contents #12, p.3-9, March 24 1986, 1986

Eugene Garfield: Fluoridation, "Texas Teeth," and the Great Conspiracy. Part 2. The Evidence, Essays of an Information Scientist, Vol.9, p.96, 1986. Current Contents #13, p.3-9, March 31, 1986

Return to Fluorine, Fluorides, & Chemical Nomenclature.

To learn how fluorine has this special ability to enter and strengthen tooth structure, you need to know that teeth – and bones – are made of the mineral apatite.

Click on atomic structure of apatite for an explanation of its beautiful structure.