H' at. wt. (natural) 1.007967
at. wt. (H') 1.007822
at. no. 1
m.p. - 259.140C
b.p. - 252.870C
density 0.08988 gm./l
density (liquid) 70.8 gm/i. (-2530C)
density (solid) 7016 gm/i. (-2620C)
valence 1.
Electronic configuration
| K |
L |
M |
N |
O |
P |
Q |
| 1 |
2 |
3 |
4 |
5 |
6 |
7 |
| s |
s p |
s p d |
s p d f |
s p d f |
s p d f |
s p d f |
| 1 |
|
|
|
|
|
|
THALLIUM (Or. thai/os, a green shoot or twig), Tl; at.
wt. 204.37; at. no. 81; m.p. 303.50C; h.p. 1457+ 100C;
sp. gr. 11.85 (200C); valence I or 3. Discovered spectro-
scopically in 1861 by Crookes. The element was named
after the beautiful gre?n spectral line, which identified the
element. The metal was isolated both by Crookes and Lamy
in 1862 about the same time. Thallium occurs in crooksite,
lorandite, and hutchinsonite. It is also present in pyrites and
is recovered from the roasting of this ore in connection with
the production of sulfuric acid. It is also obtained from the
smelting of lead and zinc ores. Extraction is somewhat
complex and depends on the source of the thallium. When
freshly exposed to air thallium exhibits a metallic luster, but
soon develops a bluish gray tinge, resembling lead in appear-
ance. A heavy oxide builds up on thallium if left in air, and in
the presence of water the hydroxide is formed. The metal is
very soft and malleable. It can be cut with a knife. Twenty
isotopic forms of thallium, with atomic masses ranging from
191 to 210 are recognized. Natural thallium is a mixture of
two isotopes. The element and its compounds are toxic and
should be carefully handled. Contact of the metal with the
skin is dangerous, and when melting the metal, adequate
ventilation should be provided. The maximum allowable
concentration of soluble thallium compounds in air is 0.1
mg/cu meter. Thallium sulfate is widely employed as a
rodenticide and ant killer. It is odorless and tasteless, giving
THE ELEMENTS~Crntinued)
no warning of its presence. The electrical conductivity of
thallium sulfide changes with exposure to infrared light and
this compound is used in photocells. Thallium bromide-
iodide crystals have been used as infrared detectors.
Thallium has been used, with sulfur or selenium and arsenic,
to produce low melting glasses which become fluid between
125 and I 500C. These glasses have properties at room tem-
peratures similar to ordinary glasses and are said to be
durable and insoluble in water. Thallium oxide has been
used to produce glasses with a high index of refraction. A
mercury-thallium alloy, which forms a eutectic at 8.5%
thallium, is reported to freeze at - 60?C, some 200C below
the freezing point of mercury. Commercial thallium metal
costs about $8/lb. It is available also in high-purity form at
a cost of about $4/oz.
© 1999 F. Davies
Delphi O.E.M. Co.
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