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

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

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.

• 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

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

Chlorides

Group 13

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.
    • GaCl_2.3: Ga₃Cl₇ = Ga^I(Ga^III
      ₂Cl₇)
    • GaCl₂ = Ga^I(Ga^IIICl₄)
  • Lower chlorides of indium:
    • InCl_1.3: In₇Cl₉ = In^I₆(In^IIICl₆)Cl₃, yellow solid stable up to 250 °C, Angew. Chem. Int. Ed. (1991) 30, 824-825
    • InCl_1.5: In₂Cl₃ = In^I₃(In^IIICl₆), colourless, Z. anorg. allg. Chem. (1981) 478, 39-51
    • InCl_1.8: In₅Cl₉ = In^I₃(In^III₂Cl₉), 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

Group 15

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)

Table of chlorides

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

• 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

Oxides

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 - -