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krypton (Kr), and xenon (Xe), all of which were discov-
ered between 1868 and 1898. In 1868, Pierre Janssen
(1824-1907), a French astronomer, observed a yellow
line in the spectrum of the sun's chromosphere. Because
no known element on Earth could account for this line,
he believed that it was due to an element unique to
the sun. Joseph Norman Lockyer (1836-1920), an
English astronomer, confirmed Janssen's findings and
named the new element helium (He), after Helios ,the
Greek god of the sun. The element was not discovered
on Earth until 1895, when Sir William Ramsay (1852-
1916), a Scottish chemist, found it in the mineral clevite .
Swedish chemists Per Theodor Cleve (after whom cle-
vite is named) and Nils Abraham Langlet found helium
in the mineral at about the same time. Helium is the
most abundant element in the universe after hydrogen.
On Earth, helium is emitted to the air following the
decay of radioactive minerals.
In 1894, Lord Baron Rayleigh ,anEnglish physi-
cist born John William Strutt (1842-1919), discovered
that nitrogen gas from the air was 0.5 percent heavier
than was that prepared chemically. He and Sir Ram-
say found that the difference was due to a previously
undiscovered gas that they called argon (Ar), after
the Greek word argos ,meaning “lazy” in reference to
the inert qualities of the gas. The two shared a Nobel
Prize for their discovery. Argon forms from the radioac-
tive decay of potassium (K). In his 1898 topic War o f
the Worlds ,H.G.Wellswrote that Martians used “toxic
brown argon gas” to attack London, but were subdued
by the common cold. However, argon is neither brown
nor poisonous at typical atmospheric concentrations. It
is colorless and odorless as a gas and liquid. Sir Ramsay,
together with M. W. Travers, went on to discover the
elements neon (Ne), krypton (Kr), and xenon (Xe), all
in 1898. The three were named after Greek words: neos
(“new”), kryptos (“concealed”), and xenos (“guest”),
respectively. The source of krypton and xenon is the
radioactive decay of elements in the Earth's crust, and
the source of neon is volcanic outgassing.
Figure 1.23. Marie Curie (1867-1934). Edgar Fahs
Smith Collection, University of Pennsylvania Library.
Prize for their fundamental research on radioactivity. In
1911, Marie Curie won a second prize for her discov-
eries of polonium and radium (Ra), a radon precursor.
Radon, itself, was discovered in 1900 by German physi-
cist Friedrich Ernst Dorn (1848-1916), who called it
radium emanation because it is a product of radioac-
tive decay of radium. The name radium is from the
Latin word radius ,meaning “ray.” Ramsay and Gray,
who isolated radon and determined its density, changed
its name to niton in 1908. In 1923, niton was renamed
radon.
1.2.3.6. Radioactive Gases
Tworadioactive elements of atmospheric importance,
polonium (Po) and radon (Rn), were discovered in
the late twentieth century. These carcinogenic ele-
ments are found in the air of many homes overlying
uranium-rich soils. In 1898, French chemists Pierre
Curie (1859-1906) and Marie Curie (1867-1934;
Figure 1.23) discovered polonium, which was named
after Marie Curie's native country, Poland. In 1903,
Pierre and Marie Curie, along with French physicist
Antoine Henri Becquerel (1852-1908), won a Nobel
1.3. Chemical Structure and Reactivity
In this section, the structure and reactivity of some
of the compounds identified previously are discussed.
Table 1.4 shows the chemical structure of selected com-
pounds. Single, double, and triple lines between atoms
denote single, double, and triple bonds, respectively.
Forsome compounds [OH(g), NO(g), NO 2 (g)], a sin-
gle dot is shown adjacent to an atom. A single dot indi-
cates that the atom has a free electron. Compounds with
 
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