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Main group 1, NCN

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"Chemistry of the Main Group Elements, Part 1"
Professor Nick Norman

General principles

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Elements

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Allotropes of boron

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Several, all based on B12 icosahedra. See Jmol model of α-rhombohedral boron.

Allotropes of carbon

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Allotropes of carbon: six crystalline forms, plus fullerenes. See Greenwood & Earnshaw (2nd Ed.) pp. 275-276.

Allotropes of tin

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α-Sn (left), β-Sn (right)
  • Two main forms: α and β
    • α-Sn, grey tin, non-metallic with the cubic diamond structure, the stable form below 13.2 °C
    • β, white tin, metallic with a tetragonal (space group I41/amd, no. 141) crystal structure, the thermodynamically stable form at room temperature
  • Problematic β→α transition at low temperature is called tin pest

Allotropes of phosphorus

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According to Greenwood and Earnshaw, there are about twenty allotropes of phosphorus, but the main ones are as follows:

  • White phosphorus, also called yellow phosphorus and α-P4, contains tetrahedral P4 molecules and melts at 44 °C. When cooled to −77 °C, α-P4 converts to a very similar low-temperature form called β-P4 that has a hexagonal crystal structure. It is highly toxic.
  • Red phosphorus is polymeric and amorphous. It is made by heating white phosphorus to about 300 °C in the absence of air. It's denser than white P (2.2 vs. 1.8 g cm−3), melts much higher (600 vs. 44 °C) and is much less reactive, and almost non-toxic.
  • Black phosphorus is the most thermodynamically stable form of phosphorus. It has three crystalline forms (orthorhombic, rhombohedral, and cubic), all consisting of infinite sheets of P atoms stacked one atop the other. There is also an amorphous form. Shown below is the orthorhombic form of black P.
  • Violet phosphorus, also known as Hittorf's phosphorus, is crystalline and has a very complicated structure, shown below. It can be formed by crystallising phosphorus from molten lead!

All solid forms of phosphorus melt to give the same liquid, which consists of P4 molecules. Gaseous phosphorus is P4 up to 800 °C, a mixture of P4 and P2 above 800°C and a 50:50 mixture of P2 and atomic P at 2800 °C

Compounds

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Chlorides

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Group 13

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Trichlorides
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Lower chlorides
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Group 14

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C, Si, Ge, Sn and Pb all form MCl4 and Ge, Sn and Pb form MX2

  • Tetrachlorides: all tetrahedral molecules, +4 oxidation state gets progressively less stable down the group
    • CCl4 – non-polar, volatile, fairly unreactive colourless liquid
    • SiCl4 – non-polar, volatile, colourless liquid, undergoes nucleophilic substitution easily, e.g. SiCl4 + 2 H2O → SiO2 + 4 HCl (hydrolysis)
    • GeCl4 – non-polar, colourless liquid
    • SnCl4 – colourless liquid, hydrolyses readily, fumes in air, often forms 6-coordinate complexes L2SnCl4
    • PbCl4 – yellow oil stable below 0 °C, decomposes to PbCl2 + Cl2 above 50 °C (G&E, pp. 381–382, Acta Cryst. (2002). E58, i79-i81)
  • Dichlorides: +2 oxidation state gets progressively more stable down the group
    • CCl2 – dichlorocarbene, a highly reactive carbene
    • SiCl2 – polymeric perchloropolysilane, (SnCl2)n, Angew. Chem. Int. Ed. (1998) 37, 1441-1442, and monomeric dichlorosilylene, reactive species
    • GeCl2 – GeCl2 is pale yellow, formed from GeCl4 + powdered Ge at 300 °C or by thermal decomp. of GeHCl3 at 70 °C (G&E, p. 376)
    • SnCl2 – tin(II) chloride, white crystalline solid, stable, reducing agent
    • PbCl2 – lead(II) chloride, white crystalline solid, much more stable than PbCl4

Group 15

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Trichlorides
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  • Trichlorides: all trigonal pyramidal molecules:
    • NCl3 − reactive yellow, oily, pungent liquid; dangerously explosive, sensitive to light, heat, and organic compounds
    • PCl3 − colourless liquid, fast and exothermic hydrolysis: PCl3 + 3H2O → H3PO3 + 3HCl
    • AsCl3 − colourless liquid, more stable wrt hydrolysis in acidic water than PCl3
    • SbCl3 − soft colorless solid with a pungent smell, hydrolyses to antimony oxychloride: SbCl3 + H2O → SbOCl + 2HCl
    • BiCl3 − hygroscopic white to yellow crystalline solid; a Lewis acid, forms a variety of chloro complexes such as [BiCl6]3−
Pentachlorides
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  • Pentachlorides: tend to be trigonal bipyramidal molecules, with 3c4e bonding to the two axial chlorides

Table of chlorides

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Main group chlorides
group →
period ↓
13 14 15 16 17
2 B
B2Cl4
BCl3
C
C2Cl4
CCl4
N
-
NCl3
O
-
-
F
-
-
3 Al
-
AlCl3
Si
-
SiCl4
P
PCl3
PCl5
S
S2Cl2
SCl2
Cl
-
-
4 Ga
GaCl
Ga3Cl7, GaCl2
GaCl3
Ge
-
GeCl2
GeCl4
As
-
AsCl3
AsCl5
Se
Se2Cl2
SeCl4
-
Br
BrCl
-
-
5 In
InCl
In5Cl9, In2Cl3, In7Cl9
InCl3
Sn
-
SnCl2
SnCl4
Sb
-
SbCl3
SbCl5
Te
Te2Cl, TeCl2
Te3Cl2
TeCl4
I
ICl
ICl3
-
6 Tl
TlCl
TlCl2, Tl2Cl3
TlCl3
Pb
-
PbCl2
PbCl4
Bi
-
BiCl3
-
Po
PoCl2
PoCl4
-
At
?
-
-

Group 16

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Oxides

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Main group oxides
group →
period ↓
13 14 15 16 17
2 B
B2O3
B6O





C
COx
CO
CO2
CO3
C3O2
C2O

N
NOx
N2O
NO
NO2
N2O4
N2O3
N2O5
O
O2
O3





F
F2O
F2O2





3 Al
Al2O3


Si
SiO2
SiO

P
P2O5
P2O3

S
SOx
SO2
SO3
Cl
ClOx
ClO2
Cl2O7
Cl2O
Cl2O3
Cl2O6
4 Ga
Ga2O3
-
Ge
GeO
GeO
As
As2O5
As2O3
Se
SeO2
SeO3
Br
-
-
5 In
In2O3
-
Sn
SnO
SnO2
Sb
Sb2O5
Sb2O3
Te
TeO2
TeO3
I
IOx
I2O4
I2O5
I4O9
6 Tl
TlO2
Tl2O
Tl2O3
-
Pb
PbOx
PbO
PbO2
Pb3O4
Bi
Bi2O3
-
Po
PoO2
PoO3
At
-
-