8. Chemistry of the Main Group Elements
A Snapshot on Main Group Chemistry
unusual bonding , structure & reactivity
8. Chemistry of the Main Group Elements
A Snapshot on Main Group Chemistry very powerful reducing agent te 2+ a − in d r o ? o ! c n - o b six r a c 2− Na2 [Ne]3s2 {Ba-cryptand} + disodide 2− M.Y. Redko et al. JACS 2003
gold(I) methanium also, in NH3(l) H. Schmidbaur et al. Na + (NH ) e − Chem. Ber. 1992 3 x
1 8. Chemistry of the Main Group Elements
A Snapshot on Main Group Chemistry very powerful reducing agent 2+ −
2− Na2 [Ne]3s2 {Ba-cryptand} + disodide 2− M.Y. Redko et al. JACS 2003
gold(I) methanium also, in NH3(l) H. Schmidbaur & F. Gabbai Na + (NH ) e − Chem. Ber. 1997 3 x
8. Chemistry of the Main Group Elements
here we go again… table salt #1 …well, not in my book!
Check out Nitrogenase or Cytochrome C-Oxidase…or Hemoglobin…
2 8. Chemistry of the Main Group Elements
Hemoglobin
8. Chemistry of the Main Group Elements
more on that later…
3 8. Chemistry of the Main Group Elements
General Trends in Main Group Chemistry
Electrical Resistivities:
far right: non-metals pnic(t)ogens (pnigo = choke), chalcogens, halogens & noble gases
middle: C: Diamond, graphite & fullerenes Si: Silicon, Ge: germanium, Sn & Pb
far left: metals alkali metals & alkaline earths: luster, high ability to conduct heat & electricity, malleability
8. Chemistry of the Main Group Elements
General Trends in Main Group Chemistry
Electrical Resistivities: Carbon conductivity 154.5 pm parallel to layers: σ = C-C 154 pm 2 C=C 134 pm 3 2.6 x 104 sp sp Ω-1cm-1 + pπz
T ¼, σ ¿ metal
conductivity perp. to layers: σ = ~2 Ω-1cm-1
T ¼, σ ¼ semiconductor
4 8. Chemistry of the Main Group Elements
General Trends in Main Group Chemistry
Electronegativities & Ionization Energies
Bond-Energy X2 Acid-Strength HX C Multiple-Bonding ly H-Bonding a m o n a w ro t- rs fi
8. Chemistry of the Main Group Elements
Oxidation – Reductions Reactions
acidic basic ΔG0 = −nFE
Frost- Diagram
+ − − − 2H + 2e -> H2 H20 + e -> OH + ½ H2
E0 = 0V E0 = −0.828V
− − − − H2 + 2e -> 2H H2 + 2e -> 2H
E0 = −2.25V E0 = −2.25V +1 0 -1 +1 0 -1 Latimer- + 0 -2.25 − -0.828 -2.25 − H H2 H Diagram H2O H2 H
5 8. Chemistry of the Main Group Elements
Oxidation – Reductions Reactions
acidic basic
0 -1 -2 Latimer- 0 -1 -2 0.695 1.763 −0.065 − 0.867 − O2 H2O2 H2O Diagram O2 H2O OH
8. Chemistry of the Main Group Elements
Hydrogen - Occurrence
most abundant element heavy water cosmic radiation in in the universe upper atmospheres 1 2 3 1H 1H 1H Protium H Deuterium D Tritium T 99.9855% 0.0145% 10-15 % 3 0 β-decay: 2He + −1e stable stable τ½ = 12.34 yrs 6 1 4 3 3Li + 0n -> 2He + 1H
6 8. Chemistry of the Main Group Elements
Hydrogen – Physical Properties
Properties H2O D2O T2O molecular weight 18.0150 20.0276 22.0315 density @ 25oC g/cm3 0.99701 1.1044 1.2138 max. density of liquid water 1.0000 1.1059 1.2150 T @ max. density in 0C 3.98 11.23 13.4 melting point in 0C 0.00 3.82 4.49 boiling point in 0C 100.00 101.42 101.51
8. Chemistry of the Main Group Elements
Hydrogen – Chemical Properties
− The hydride anion H : strong reducing agent (E0 = −2.25 V)
& good ligand
− 3+ + − (BH4 )3Al [(en)2Li ]AlH4 (Ph3P)ReH8
7 8. Chemistry of the Main Group Elements
Ionic (salt-like) Hydrides: NaH, CsH, MgH2
ΔE.N.: 1.3 (CsH) – 1.0 (MgH2) × only 30 – 18% ionic character ionic radius (exp.: 1.39 – 1.14, calc.: 2.04 Å)
NaH
Metallic (interstitial) Hydride: PdH2, UH3 electr. conductance: M—M and M—H “metallic bonding”
+ 3+ hydridic H: UH3 + 3H Æ U + 3H2 protic H: cathod. H2-evolution from Pd sponge electrolysis of PdH2 [Pd]—Hads
Covalent (molecular) Hydride: B2H6, CH4, NH3 molecular structures: Gillespie & Nyholm formation of polymers, dimers, oligomers & complex structures Diborane
8. Chemistry of the Main Group Elements
• Ammonia-( Haber-Bosch) Synthesis: N2 + 3H2 2NH3 (a-Fe Cat., 500 °C, 400 bar)
• Methanol Synthesis: CO + 2H2 CH3OH (Cu/ZnO/Al2O3 – Cat., 200 °C, p)
• Hydrogenation: R2C=CR2 + H2 R2HC—CHR2 (Cat.: Ni, Pd, Pt etc)
Reduction agent: MOx + H2 M + xH2O (high Temp.)
• Rocket Fuel and Energy: H2 + O2 2H2O + Energy
8 8. Chemistry of the Main Group Elements
The Alkaline-Metals – The Elements Lithium (Li) Sodium (Na) Potassium (K)
τ½ = 22 min Rubidium (Rb) Caesium (Cs) Francium (Fr)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
8. Chemistry of the Main Group Elements
The Alkaline-Metals – Physical Properties
9 8. Chemistry of the Main Group Elements
The Alkaline-Metals – Chemical Properties
2 M + 2H2O -> 2 MOH + H2
M + O2 -> M2O, M2O2, MO2
+ − M + xNH3 -> M + e(NH3)x
− − RC≡CH + e -> RC≡C + ½ H2 − 2− S8 + 2e -> S8
8. Chemistry of the Main Group Elements
The Alkaline-Metals – Chemical Properties
10 8. Chemistry of the Main Group Elements
The Alkaline-Metals – Chemical Properties inverse Na hydride
[(15crown5)Cs]+e − an “electride” [(15crown5)Rb]+Na −
8. Chemistry of the Main Group Elements
The Alkaline-Metals – Chemical Properties
Bis(15crown5)cesium electride, space fill (left) and stick-model (right) with cell axis – Where is the electron? alkalide counter- part structures large are known , e.g.: + − cationic (15C5)2Cs Na complexes 8 – 10 Å
electron trapping cavity 3.7 – 4.8 Å J. L. Dye Acta Cryst. C (1990) 46, 1831
11 8. Chemistry of the Main Group Elements
The Alkaline-Metals – Chemical Properties • Electrons can also be trapped in solid matrices (lattices) of simple salts (color-center or F-center, German: Farbe)
• Irradiation of salts with X-rays or ionizing radiation produces colored defects. The color of the defect depends on the nature of the host lattice (dimensions)
http://mrsec.wisc.edu/Edetc/cineplex/Fcenter/text.html
8. Chemistry of the Main Group Elements
The Alkaline-Earths – The Elements Beryllium (Be) Magnesium (Mg) Calcium (Ca)
τ½ = 1600 yrs Strontium (Sr) Barium (Ba) Radium (Ra)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
12 8. Chemistry of the Main Group Elements
The Alkaline-Earths – Physical Properties
8. Chemistry of the Main Group Elements
The Alkaline-Earths – Chemical Properties
+ 2+ Mg + 2H -> Mg + H2
Ca + 2H2O -> Ca(OH)2 + H2 Elements in Group 2 have similar chemical properties; tendency to loose two electrons to achieve noble gas e − conf.
Exception: Beryllium, covalent rather than ionic bonding:
2-electron-3-center bonding (as in B2H6, Al2Cl6...)
13 8. Chemistry of the Main Group Elements
The Group 13 Elements
Boron (B)
non-metal
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
8. Chemistry of the Main Group Elements
Diborane (B2H6) convenient laboratory synthesis: @ RT
3Na(BH4) + 4 Et2O • BF3 -> 2B2H6 + 3NaBF4 + 4Et2O
industrial synthesis: @ 450K
2BF3 + 6NaH -> B2H6 + 6NaF
0 B2H6 (ΔfH = +36 kJ/mol) air-moisture sensitive
explodes with O2 (stable borates) very toxic
controlled pyrolysis of B2H6 via reactive BH3 intermediates & H2 form.
14 8. Chemistry of the Main Group Elements
Boranes: Wade’s Rules
2− BnHn closo
BnHn+4 nido
BnHn+6 arachno
controlled pyrolysis of B H BnHn+8 hypho 2 6 via reactive BH3 intermediates
8. Chemistry of the Main Group Elements
B12 B11 B10 B9 B8 B7 B6 B5 B4 closo-
2- 2- B6H6 B12H12 Oh Ih nido-
and by the way… Al does it as well arachno-
15 8. Chemistry of the Main Group Elements
8. Chemistry of the Main Group Elements
Boron-Neutron Capture therapy (BNCT) selective cell-killing with slow neutrons
thermal neutron
no hit- ionizing α-particles no harm travel one cell-diameter, very destructive
16 8. Chemistry of the Main Group Elements
Bonding in Diborane (B2H6)
8. Chemistry of the Main Group Elements
Bonding in Diborane (B2H6)
17 8. Chemistry of the Main Group Elements
Bonding in Diborane (B2H6)
8. Chemistry of the Main Group Elements
Bonding in Diborane (B2H6)
H don’t forget …similar to about B BB B B H in higher borane clusters
18 8. Chemistry of the Main Group Elements
The Group 14 Elements
Carbon (C)
non-metal
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
8. Chemistry of the Main Group Elements
The Group 15 Elements
Nitrogen (N)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
19 8. Chemistry of the Main Group Elements
The Group 16 Elements
Oxygen (O)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
8. Chemistry of the Main Group Elements
The Group 17 Elements
Fluorine (F)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
20 8. Chemistry of the Main Group Elements
The Group 18 Elements
Helium (He)
http://www.chemsoc.org/viselements/pages/pertable_fla.htm
8. Chemistry of the Main Group Elements
The Group 18 Elements
Discovered : by Sir William Ramsay in London, and independently by P.T. Cleve and N.A. Langlet in Uppsala, Sweden in 1895
Discovered : by Sir William Ramsay and Discovered : by Sir M.W. Travers in 1898 William Ramsay and Discovered : 1899 by Lord M.W. Travers in 1898 Origin : Greek ‘xenos’, Rayleigh and Sir William meaning strange. Ramsay Origin : Greek ‘kryptos’, Discovered : by Sir William meaning hidden Description : Ramsay and M.W. Travers Origin : Greek ‘argos’ A colorless, odorless gas in 1898 (London, UK) meaning inactive. Description : that makes up 0.086 Description : A colorless, odorless gas parts per million of the A colorless, odorless gas that Origin : Greek ‘neos’ (new) Description : that is inert to everything atmosphere. About half is totally unreactive. It is The third most abundant but fluorine gas. The a ton a year is produced isotope krypton 86 has a from liquid air and extracted from natural gas Description : gas, making up one line in its atomic used for research wells, some of which contain A colorless, odorless gas percent of the atmos- gas that is 7% helium. It is phere. The quantity has spectrum that is now the purposes. that comprises 18 parts per standard measure of used in deep sea diving for million of air. Neon will increased since the Earth balloons and, as liquid was formed because length : 1 meter is not react with any other defined as exactly helium , for low temperature substance. It is produced radioactive potassium research. The Earth’s turns into argon as it 1,650,763.73 wavelengths from liquid air for of this line. Krypton is one atmosphere contains 5 parts ornamental lighting (i.e. decays. Argon is a per million by volume, colorless, odorless gas of the rarest gases in the neon signs) because it Earth’s atmosphere, totaling 400 million tons, but glows red when an that is totally inert to it is not worth extracting it other substances, and for accounting for only 1 electrical discharge is part per million by from this source at present. passed through it. this reason it is ideal in light bulbs. volume.
21