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Inorganic Exotic Molecules 819

which we will discuss for our own enunciated and id- A. Energy and Length
iosyncratic, internally and intellectually consistent, rea-
We start our study with a brief interlude on units. We
sons. Having decided to include such species (and like-
care about energy and length but the relevant size to us
wise some simple, classically well characterized and
as chemists is not relevant to us as human beings. As
classic inorganic compounds), we conclude that “ex-
chemists, we have two generally commonly used set of
otic” does not necessarily mean ephemeral, fragile, or −1 −1
units, kcal mol and kJ mol . In this study we will use
even rare, and “inorganic” has long not meant the ab- −1
the latter, where by definition 1 kcal mol equals 4.184 kJ
sence of carbon. Again, poetry more than chemistry −1
mol . In chemical discussions, the unit of length—
from one of the article contributors is offered as an
atomic sizes, bond lengths (interatomic distances)—has
answer:
˚
typically been A (angstroms), where, again by definition,
˚
1 A equals 10 −8 cm or 10 −10 m because that is the typ-
Molecules long-lived and transient,
ical interatomic spacing. More recently, length is often
From creative minds, fingers agile
˚
Some molecules new, some ancient, written in picometers (pm; 1 A equals 100 pm). Purely
Like glass, fluid, frozen, fragile for personal reasons, we have rarely done so. Objects of
Flowing like the tidal currents scientific and technological interest have gotten smaller—
Like the sands and like the sea “nanotechnology” has become a word for our era and a
Lessened carbon occurrence hope for the next. Molecular species have gotten bigger—
˚
To students of chemistry the nanometer (nm; 10 A equals 1 nm) is a convenient
length scale and “nano” is a convenient, confluent prefix.
Finally, we turn to the relatively prosaic question of
In this text we will use both angstroms and nanometers
sources of information. We would have preferred to rec-
length units, depending on the context.
ommend only suitably advanced textbooks and articles in
review journals and monographs. Somehow these sources
appear more permanent than papers in the primary re-
B. A Review of Atoms—Hydrogen
search journals, yet by definition secondary and tertiary
and Its Components
sources of information are more dated. Wonders abound
in all of them. We admit arbitrariness in our choices— We start our study of exotic inorganic compounds with a
no universal criterion for their inclusion other than the brief review of atoms to emphasize the strangeness of or-
presence of exotic chemistry can be offered. There was dinary chemical reality. We deal here with the simplest of
too much, rather than too little, to choose among. After chemically relevant species, and perhaps the most surpris-
all, we were not allowed to write our own volume, “The ing phenomena. To chemists these species and associated
Encyclopedia of Exotica.” We close the introduction with phenomena may appear “normal” and so our discussion
two quotes that provided us a guideline. The first is from may appear either prosaic or philosophical. Accordingly,
a psalm that provides implicit chastisement for whatever the reader may feel our text belongs, at best, in a fresh-
choice we made; the second is from the Mishnah, the legal man chemistry course or one in physics and/or philoso-
core of the Talmud, which offers a source of reassurance phy. We shall simply tell our stories and hope the reader
for our efforts. will continue on to read the following vignettes about the
science of “bigger” species, those with more nuclei and
electrons.
(i) “The stone that the builders rejected has become the
Consider atomic hydrogen and its components. In its
chief cornerstone” (Psalm 118:22, Revised Standard
most common isotopic form, it has one proton and one
Bible).
electron. The mass ratio of these two components is nearly
(ii) “It is not up to you to finish the work, yet you are not
2000:1. Why are the two parts so different in mass? Pro-
free to avoid it” Pirke Avot 2:16; Kravitz and
tons are so massive that they, individually and therefore in
Olitzky, 1993).
assemblages, may be assumed to be stationary. From this
the concept of molecular and geometric structure arises:
Now to the science.
bond lengths and angles require fixed positions. The mass
of the electron is so low that we should consider elec-
trons inherently delocalized. From this the concept of
I. ATOMS AND THE NATURE OF MATTER orbitals and electronic structure unavoidably arises: we
should not talk about dots and lines that describe fixed
Atoms and molecules are not part of conventional, daily electrons. At least as importantly, atoms, molecules, and
human experience. all the chemical-based reality from legumes to lepidoptera