Page 209 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

P1: GSS Final Pages
Encyclopedia of Physical Science and Technology EN009F-398 July 6, 2001 20:34

18 Main Group Elements

Research with an alkali-promoted (potassium or K 2 O) Hydrazine, N 2 H 4 , is a colorless liquid with a weakly
ruthenium catalyst has demonstrated that ammonia syn- ammoniacal odor. Its density, boiling point (114 C), and
◦
thesis can be effected at lower temperatures and pressures melting point (2 C) are fairly close to those of water. Hy-
◦
than those required by the Haber process. As the price of drazine and its monomethyl and dimethyl derivatives are
energy increases, ruthenium catalysis might become in- used as rocket fuels. A more mundane application of hy-
creasingly important, because the energy-expensive com- drazine is its use in water treatment and in cleaning steam
pression process could be avoided. Another advantage of boilers.
ruthenium if its diminished susceptibility to poisoning by
H H H H H H
H 2 O and CO. Ruthenium catalysts can carry out the direct
N N H N
synthesis of ammonia from N 2 , CO, and H 2 O: N H N H C N
H H H C H
Ru−K 2 O H C
3H 2 O + 3CO + N 2 −−−−→ 3CO 2 (g) + 2NH 3 (g) H H
H H
Hydrazine Monomethylhydrazine Dimethylhydrazine
Ammonia, a colorless gas with a distinctive, highly ir-
ritating, penetrating odor, is a potent heart stimulant. It
Hydrazoic acid, HN 3 , is a colorless, explosive liquid.
is highly soluble in water, boils at −33 C, and melts at
◦
It is a weak acid whose salts are called azides. Heavy-
−78 C. The shape of the ammonia molecule is that of a
◦
metal azides, like the acid, are unstable and are employed
trigonal pyramid; the lone pair on the nitrogen atom helps
as detonators for explosives. Sodium azide, NaN 3 , is used
to explain the highly polar nature and the basicity of the
by biochemists to study cellular respiration. The linear,
molecule.
−
symmetric azide ion, [N N N] , serves as an inhibitor
Liquid ammonia has certain solvent properties like
of the key electron transfer step.
those of water; however, liquid ammonia will dissolve the
alkali metals (sodium, potassium, etc.) and the heavier al-
kalineearthmetals(calcium,strontium,barium)togivein- B. Halides
tensely blue, conducting solutions. The sodium solution is
The important nitrogen halides include the following:
widely used as a reducing agent in organic syntheses. The
NF 3 ,N 2 F 2 ,N 2 F 4 , NCl 3 , NBr 3 , and NI 3 . The structures
unbalanced equation is presented in textbooks as follows:
of the four fluorides have been determined and are not un-
R H expected in terms of valence-shell electron-pair repulsion
Na, NH 3(1)
R C C R C C theory (VSEPR) for predicting molecular geometries.
H R
F F
The primary use of ammonia (∼80%) in the United N N N N N F N N F
States is in fertilizers, either as anhydrous ammonia or as F F F F F F
F trans cis
the salts ammonium nitrate and ammonium sulfate. Other
uses include conversions to nitric acid and urea. The re-
The trihalides of nitrogen provide sharp contrasts in
action for the syntheses of the ammonia derivatives are as
their stability and reactivity. NF 3 is a stable gas that re-
follows.
sists hydrolysis by water, NCl 3 is an unstable liquid that
1. Ammonium nitrate:
decomposes explosively and hydrolyzes readily, and NBr 3
is very unstable and decomposes explosively even at very
NH 3 + NHO 3 → NH 4 NO 3
low temperatures. Pure NI 3 has not been isolated. Crystals
2. Ammonium sulfate: resulting from the action of iodine on ammonia are rep-
resented by the formula NI 3 · NH 3 . This unstable adduct,
2NH 3 + H 2 SO 4 → (NH 4 ) 2 SO 4
often prepared for chemical demonstrations, can be ex-
3. Nitric acid: ploded by the slightest tickling with a feather.
4NH 3 (g) + 5O 2 (g) → 4NO (g) + 6H 2 O (g)
C. Nitrogen Oxides
2NO (g) + O 2 (g) → 2NO 2 (g)
Nitrogen forms several oxides, some of which were known
3NO 2 + H 2 O → HNO 3 + NO
to investigators of the eighteenth century. A brief tabular
4. Urea: presentation of the oxides appears in Table V.
The three nitrogen oxides NO, NO 2 , and NO 3 are para-
O
heat,pressure || magnetic, odd-electron species. Both NO and NO 2 are
2NH 3 + CO 2 −−−−−−→ H 2 N C NH 2 + H 2 O important in the synthesis of nitric acid from ammonia;