Inorganic Chemistry
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Inorganic Chemistry


DisciplinaQuímica Inorgânica I3.901 materiais31.960 seguidores
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the pair of atoms BN being isoelectronic with CC. (For example, the ion [NH3BH2NH3]
+ is analogous to propane, CH3CH2CH3.) 
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Boron nitride BN can form two solid structures, one containing hexagonal BN layers similar to 
graphite, and the other with tetrahedral sp3 bonding like diamond (see Topic D2). Borazine B3N3H6
has a 6-\u3c0-electron ring like benzene (5 shows one resonance form; see Topic C7). Although BN is 
very hard and resistant to chemical attack, borazine is much more reactive than benzene and does not 
undergo comparable electrophilic substitution reactions. The difference is a result of the polar B-N 
bond, and the more reactive B-H bonds. 
 
Boron forms a binary carbide, often written B4C but actually nonstoichiometric, and compounds 
with most metals. The stoichiometries and structures of these solids mostly defy simple 
interpretation. Many types of chains, layers and polyhedra of boron atoms are found. Simple 
examples are CaB6 and UB12, containing linked octahedra and icosahedra, respectively. 
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Section F\u2014Chemistry of nonmetals 
F4 
CARBON, SILICON AND GERMANIUM 
The elements 
With the valence electron configuration s2p2 the nonmetallic elements of group 14 can form 
compounds with four tetrahedrally directed covalent bonds. Only carbon forms strong multiple 
bonds, and its compounds show many differences in structure and properties from those of Si and 
Ge. Like the metallic elements of the group (Sn and Pb), germanium has some stable divalent 
compounds. 
The abundances of the elements by mass in the crust are: C about 480 p.p.m., Si 27% (second only 
to oxygen), and Ge 2 p.p.m. Carbon is present as carbonate minerals and in smaller amounts as the 
element and in hydrocarbon deposits. It is important in the atmosphere (as the greenhouse gas CO2; 
see Topic J6) and is the major element of life. Silicate minerals are the dominant chemical 
compounds of the crust and of the underlying mantle (see Topic J2). Germanium is widely but thinly 
distributed in silicate and sulfide minerals. 
All three elements can crystallize in the tetrahedrally bonded diamond structure (see Topic D2). 
Si and Ge are semiconductors (see Topic D7). Carbon has other allotropes. Graphite is the 
thermodynamically stable form at ordinary pressures, diamond at high pressures. More recently 
discovered forms include buckminsterfullerene C60, higher fullerenes such as C70, and nanotubes 
composed of graphite sheets rolled into cylinders. In these structures carbon forms 
Key Notes 
The elements Carbonates and reduced forms of carbon are common on Earth, and silicates make up the 
major part of the crust; germanium is much less common. All elements can form the 
diamond structure; graphite and other allotropes are unique to carbon. 
Hydrides and 
organic 
compounds 
Silanes and germanes are less stable than hydrocarbons. Double bonds involving Si and Ge 
are very much weaker than with C. 
Halides Halides of all the elements have similar formulae and structures. Those of Si and Ge (but 
not of C) are Lewis acids and are rapidly hydrolyzed by water. 
Oxygen 
compounds 
Carbon oxides are molecular with multiple bonds, those of Si and Ge polymeric in 
structure. Carbonates contain simple ions, but silicates and germanates have very 
varied and often polymeric structures. 
Other 
compounds 
Compounds with S and N also show pronounced differences between carbon and the other 
elements. Many compounds with metals are known but these are not highly ionic. Metal-
carbon bonds occur in organometallic compounds. 
Related topics Introduction to nonmetals (F1) 
Organometallic compounds (H10) 
Geochemistry (J2) 
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three \u3c3 bonds, the remaining valence electron being in delocalized \u3c0 orbitals analogous to those in 
benzene (see Topic C7). 
The elements can be produced by reduction of oxides or halides. Highly divided carbon black is 
used as a catalyst and black pigment, and impure carbon (coke) for reducing some metal oxides (e.g. 
in the manufacture of iron; see Topic B4). Pure silicon prepared by reduction of SiCl4 with Mg is 
used in electronics (\u2018silicon chips\u2019) although much larger quantities of impure Si are used in steels. 
Hydrides and organic compounds 
Compounds of carbon with hydrogen and other elements form the vast area of organic chemistry. 
Silanes and germanes are Si and Ge analogs of methane and short-chain saturated hydrocarbons, 
and can be prepared by various methods, such as reduction of halides with LiAlH4: 
 
They are much more reactive than corresponding carbon compounds and will inflame spontaneously 
in air. Stability decreases with chain length in series such as 
 
Many derivatives can be made where H is replaced by monofunctional groups such as halide, alkyl, 
\u2212NH2. Many Si and Ge compounds are similar in structure to those of carbon, but trisilylamine 
(SiH3)3N and its germanium analog differ from (CH3)3N in being nonbasic and having a geometry 
that is planar rather than pyramidal about N. This suggests the involvement of the N lone-pair 
electrons in partial multiple bonding through the valence expansion of Si or Ge (see Topic C2, 
Structure 8). 
Si and Ge analogs of compounds where carbon forms double bonds are much harder to make. 
(CH3)2SiO is not like propanone (CH3)3C=O, but forms silicone polymers with rings or chains 
having single Si-O bonds (1). Attempts to make alkene analogs R2Si=SiR2 (where R is an organic 
group) generally result in single-bonded oligomers, except with very bulky R\u2212 groups such as 
mesityl (2,4,6(CH3)3C6H2\u2212), which prevent polymerization. 
 
Halides 
All halides EX4 form tetrahedral molecules (point group Td). Mixed halides are known, as well as 
fully or partially halogen-substituted catenated alkanes, silanes and germanes (e.g. Ge2Cl6). Unlike 
the carbon compounds, halides of Si and Ge are Lewis acids and readily form complexes such as 
[SiF6]
2\u2212. Attack by Lewis bases often leads to decomposition, and thus rapid hydrolysis in water, 
unlike carbon halides, which are kinetically more inert. 
Divalent halides EX2 can be made as reactive gas-phase species, but only for Ge are stable 
noncatenated GeII compounds formed. They have polymeric structures with pyramidal coordination 
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as with SnII (see Topic G6). The compound CF formed by reaction of fluorine and graphite has 
one F atom bonded to every C, thus disrupting the \u3c0 bonding in the graphite layer but retaining the \u3c3 
bonds and 
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giving tetrahedral geometry about carbon. (Bromine forms intercalation compounds with graphite; 
see Topic D5.) 
Oxygen compounds 
Whereas carbon forms the molecular oxides CO and CO2 with multiple bonding (see Topics C1 and 
C5), stable oxides of Si and Ge are polymeric. Silica SiO2 has many structural forms based on 
networks of corner-sharing SiO4 tetrahedra (see Topic D3). GeO2 can crystallize in silica-like 
structures as well as the rutile structure with six-coordinate Ge. This structure is stable for SiO2 only 
at very high pressures, the difference being attributable to the greater size of Ge. Thermodynamically 
unstable solids SiO and GeO can be made but readily disproportionate to the ioxide. 
CO2 is fairly soluble in water but true carbonic acid