User:Benjah-bmm27/degree/2/NCN

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

General principles

 * Ionization potentials (of the elements)
 * Inert pair effect
 * Electronegativity
 * Coordination geometry
 * Coordination number
 * Ionic radius
 * Covalent radius
 * Derivation of the structures of group 14-17 elements by breaking bonds in the cubic diamond structure: examine in Jmol.



Elements

 * Allotropy — like isomerism and/or polymorphism, but for elements instead of compounds: different structural forms of the same element

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

Allotropes of carbon
Allotropes of carbon: six crystalline forms, plus fullerenes. See Greenwood & Earnshaw (2nd Ed.) pp. 275-276.
 * Graphite: α and β forms, very close in energy (~ 0.6 kJ mol−1). The α form is the normal one, layers stacked ABAB...
 * Diamond: cubic diamond (all chair conformation) (Jmol) and the exceedingly rare hexagonal diamond (Lonsdaleite) (chair and boat conformations) (Jmol).
 * diamond vs. graphite, taught beautifully
 * Chaoite (existence disputed)
 * Carbon(VI)

Allotropes of tin

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


 * Diphosphorus, P2, exists in the gas phase at around 800 °C


 * 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.


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 * Tetraphosphorus-gas-2D-dimensions.png || Tetraphosphorus-3D-balls.png || White-phosphorus-xtal-3D-balls.png
 * }


 * 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.


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 * Schwarzer Phosphor.svg || Black-phosphorus-sheet-A-3D-balls.png || Black-phosphorus-B-3D-balls.png
 * }


 * 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!


 * {|align="center" class="wikitable"


 * Violet-phosphorus-chain-from-xtal-3D-balls.png || Violet-phosphorus-chains-connecting-from-xtal-3D-balls.png || Violet-phosphorus-chains-crossing-from-xtal-3D-balls.png || Violet-phosphorus-layers-from-xtal-3D-balls.png
 * }

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

 * Oxidation state
 * Radicals, dimers, unpaired electrons, electron pairs

Trichlorides

 * BCl3 trigonal planar
 * AlCl3 ionic, octahedral Al (YCl3 structure)
 * GaCl3 dimeric, tetrahedral Ga — Jmol
 * InCl3 ionic, octahedral In (YCl3 structure)
 * TlCl3 ionic, octahedral Tl (YCl3 structure)



Lower chlorides

 * Lower chlorides much more common as group is descended:
 * Many lower chlorides of gallium:
 * GaCl: red solid, disproportionates above 0 °C.
 * GaCl2.3: Ga3Cl7 = GaI(Ga$III 2$ Cl7)
 * GaCl2 = GaI(GaIIICl4)
 * Lower chlorides of indium:
 * InCl1.3: In7Cl9 = InI6(InIIICl6)Cl3, yellow solid stable up to 250 °C, Angew. Chem. Int. Ed. (1991) 30, 824-825
 * InCl1.5: In2Cl3 = InI3(InIIICl6), colourless, Z. anorg. allg. Chem. (1981) 478, 39-51
 * InCl1.8: In5Cl9 = InI3(InIII2Cl9), Z. anorg. allg. Chem. (1978) 445, 140-146, Z. anorg. allg. Chem. (1983) 503, 126-132
 * TlCl much more stable than TlCl3 due to inert pair effect

Group 14
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

Trichlorides

 * 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

 * Pentachlorides: tend to be trigonal bipyramidal molecules, with 3c4e bonding to the two axial chlorides
 * NCl5 unknown, N(V) too small and too oxidising
 * PCl5 − colourless crystalline solid, [PCl4+][PCl6−], but neutral, monomeric, trigonal bipyramidal PCl5 molecules in the gas phase
 * AsCl5 − pale yellow crystalline solid, unstable above −50 °C, As(V) less stable and more oxidising than P(V) and Sb(V) due to poorly shielding full 3d subshell
 * first prepared in 1976: AsCl3 in liquid Cl2 at −105 °C, exposed to UV, Angew. Chem. Int. Ed. (1976) 15, 377-378
 * SbCl5 − extremely viscous, syrupy, colourless or yellow fuming liquid
 * BiCl5 unknown, probably less stable than SbCl5 due to lanthanide contraction (poorly shielding 4f subshell) (G&E p. 562) and/or inert pair effect (NCN)

Group 16

 * Many binary Cl-O compounds, but they're better thought of as oxides of chlorine: see chlorine oxides
 * S2Cl2, SCl2
 * Se2Cl2, SeCl2, SeCl4
 * TeCl2, TeCl4
 * PoCl2, PoCl4