The Foundations of Chemistry

24-2 Xenon Compounds 943

THE NOBLE GASES (GROUP VIIIA)

OCCURRENCE, USES, AND PROPERTIES

The noble gases are very low-boiling gases. Except for radon, they can be isolated by frac-
tional distillation of liquefied air. Radon is collected from the radioactive disintegration
of radium salts. Table 24-1 gives the percentage of each noble gas in the atmosphere.
Helium is produced in the United States from some natural gas fields. This source was
discovered in 1905 by H. P. Cady and D. F. McFarland at the University of Kansas, when
they were asked to analyze a nonflammable component of natural gas from a Kansas gas
well. Uses of the noble gases are summarized in Table 24-2.
The noble gases are colorless, tasteless, and odorless. In the liquid and solid states the
only forces of attraction among the atoms are very weak dispersion forces. Polarizability
and interatomic interactions increase with increasing atomic size, and so melting and
boiling points increase with increasing atomic number. The attractive forces among He
atoms are so small that He remains liquid at 1 atmosphere pressure even at a tempera-
ture of 0.001 K.

XENON COMPOUNDS

Until the early 1960s, chemists believed that the Group VIIIA elements would not combine
chemically with any elements. In 1962, Neil Bartlett (1932– ) and his research group at
the University of British Columbia were studying the powerful oxidizing agent PtF 6. They

24-2

24-1

Br Kr

IXe

At Rn

Cl Ar

F Ne

He

VIIA

Si P S

Se

Te

N

VIIIA

Radon is continually produced in small

amounts in the uranium radioactive

decay sequence (Section 26-11). Radon

gas is so unreactive that it eventually

escapes from the soil. Measurable

concentrations of radon, a radioactive

gas, have been observed in basements

of many dwellings.

A pressure of about 26 atmospheres is

required to solidify He at 0.001 K.

The noble gases are often called the

rare gases. They were formerly called

the “inert gases” because it was

incorrectly thought that they could not

enter into chemical combination.

TABLE 24-1 Percentages (by volume) of Noble Gases in the Atmosphere

He Ne Ar Kr Xe Rn

0.0005% 0.015% 0.94% 0.00011% 0.000009%
0%