2: WHAT IS 'FLUORIDE' [ Main source of information: Infopedia, v2.0 ]

It is unusual to find someone who has not heard of fluoride. Conversely, it is equally unusual to find someone who can explain precisely what fluoride is. It is an indictment of our educational system that we are not told more about a chemical which threatens to have an enormous impact on our lives. So what exactly is fluoride?

Firstly, a lesson in geology. The earth consists of five parts: the atmosphere ( gaseous [air] ), the hydrosphere ( liquid [water] ) and the third, fourth, and fifth, the lithosphere, mantle, and core. The lithosphere, consists mainly rocky crust of the earth, and extends to depths of 100 km. The lithosphere comprises two shells - the crust and upper mantle and are divided into tectonic plates.

The rocks of the lithosphere are almost entirely made up of 11 elements, which together account for about 99.5% of its mass. The most abundant is oxygen (about 46.60% of the total), followed by silicon (about 27.72%), aluminum (8.13%), iron (5.0%), calcium (3.63%), sodium (2.83%), potassium (2.59%), magnesium (2.09%) and titanium, hydrogen, and phosphorus (totalling less than 1%). In addition, 11 other elements are present in trace amounts of from 0.1 to 0.02%. These elements, in order of abundance, are carbon, manganese, sulfur, barium, chlorine, chromium, fluorine, zirconium, nickel, strontium, and vanadium. The elements are present in the lithosphere almost entirely in the form of compounds rather than in their free state. These compounds exist almost entirely in the crystalline state, so each is, by definition, a mineral.

Fluorine ( From the Latin fluo, meaning "flow").

Fluorine is a member of the chemical family called the halogens, also composed of elements: chlorine, bromine, iodine and astatine. A non-metallic element, fluorine ( Symbol F ) is a pale yellowish flammable irritating toxic diatomic gas which is slightly heavier than air. It is also poisonous, corrosive and the most chemically ‘active' of all the non-metallic elements. It was discovered in 1771 by the Swedish chemist Carl Wilhelm Scheele and was isolated in 1886 by the French chemist Henri Moissan.

Periodic Table:

Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Period 1 2 3 4 5 6 7 *Lanthanoids •Actinoids
1
H
2
He
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
10
Ne
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
19
K
20
Ca
21
Sc
22
Ti
23
V
24
Cr
25
Mn
26
Fe
27
Co
28
Ni
29
Cu
30
Zn
31
Ga
32
Ge
33
As
34
Se
35
Br
36
Kr
37
Rb
38
Sr
39
Y
40
Zr
41
Nb
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
55
Cs
56
Ba
* 71
Lu
72
Hf
73
Ta
74
W
75
Re
76
Os
77
Ir
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
87
Fr
88
Ra
103
Lr
104
Rf
105
Db
106
Sg
107
Bh
108
Hs
109
Mt
110
Uun
111
Uuu
112
Uub
113
Uut
114
Uuq
115
Uup
116
Uuh
117
Uus
118
Uuo
* 57
La
58
Ce
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
67
Ho
68
Er
69
Tm
70
Yb
89
Ac
90
Th
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cf
99
Es
100
Fm
101
Md
102
No

Notes

Note that elements 113, 115, and 117 are not known, but are included in the table to show their expected positions. There are unconfirmed reports for the observation of elements 114 (ununquadium), 116 (ununhexium), and 118 (ununoctium) and so these elements are also included.

Fluorine occurs naturally in the combined form as fluorite ( or fluorspar ), cryolite and apatite. Apatite ( from the Greek ‘apate' meaning “deception” ), which is made up mainly of phosphate of lime, is a crystal which was once used in the *preparation of fertilizer.

*Phosphate rock is now used in place of mineral phosphates of lime.

Fluorine also occurs as fluorides in seawater, rivers, and mineral springs, in the stems of certain grasses, and in the bones and teeth of animals.

Fluorine Compounds.

Hydrofluoric acid (hydrogen fluoride, HF or H2F2 ), one of the most important fluorine compounds, is prepared by heating calcium fluoride in sulphuric acid. The aqueous solution of this acid, generally used commercially, is obtained by passing the anhydrous hydrogen fluoride vapors into a leaden receiver containing distilled water, thus yielding the acid in dilute form. Hydrofluoric acid is extremely corrosive and must be preserved in lead or steel containers. Hydrofluoric acid has the property of dissolving glass, and this property is used in a common test for the presence of a fluoride; hydrofluoric acid is also used extensively in various forms of glass etching, such as the marking of divisions on thermometer tubes and the etching of designs on glassware, and in other forms of ceramic etching, such as pottery decoration.

Another fluorine compound, *hydrofluosilicic acid, combines with such bases as sodium and potassium to form salts called fluosilicates or silicofluorides. Fluorine and many fluorides, such as hydrogen fluoride and sodium fluoride, are extremely poisonous.

*Also known as hexafluorosilicic acid ( H2SiF6 ), which is used to fluoridate water supplies. See Infodoc F03 for an indication of toxicity.

The Truth About Fluoride