A Snapshot on Main Group Chemistry - inorganic chemistry 8a small.pdf · A Snapshot on Main Group Chemistry 8. Chemistry of the Main Group Elements s ix - c o o r d in a t e c a r

1

8. Chemistry of the Main Group Elements

unusual bonding , structure & reactivity

A Snapshot on Main Group Chemistry


six-c

oord

inate

carb

on!?

gold(I) methaniumH. Schmidbaur et al. Chem. Ber. 1992

2+

{Ba-cryptand} + disodide 2−

M.Y. Redko et al. JACS 2003

very powerfulreducing agent

Na22−

−


also, in NH3(l)Na + (NH3)xe −

[Ne]3s2

2


very powerfulreducing agent

Na22−

gold(I) methaniumH. Schmidbaur & F. Gabbai Chem. Ber. 1997

2+ −


M.Y. Redko et al. JACS 2003

also, in NH3(l)Na + (NH3)xe −

[Ne]3s2

{Ba-cryptand} + disodide 2−


here we goagain…table salt #1

…well, notin my book!

Check out Nitrogenaseor CytochromeC-Oxidase…orHemoglobin…

3


Hemoglobin


more on that later…

4


General Trends in Main Group Chemistry

Electrical Resistivities:

far left: metalsalkali metals & alkaline earths: luster, high ability to conduct heat & electricity, malleability

far right: non-metalspnic(t)ogens (pnigo = choke), chalcogens, halogens & noble gases

middle: C: Diamond, graphite & fullerenesSi: Silicon, Ge: germanium, Sn & Pb



Electrical Resistivities: Carbon

sp2

+ pπz

sp3

conductivityparallel to layers: σ =2.6 x 104

Ω-1cm-1

T ¼, σ ¿ metal

conductivityperp. to layers: σ =~2 Ω-1cm-1

T ¼, σ ¼ semiconductor

C-C 154 pmC=C 134 pm

154.5 pm

5



Electronegativities & Ionization Energies

first-

row a

nomaly

Bond-Energy X2Acid-Strength HXC Multiple-BondingH-Bonding


Oxidation – Reductions Reactions

2H+ + 2e − -> H2

E0 = 0V

H2 + 2e − -> 2H−

E0 = −2.25V

H+ H2 H−

+1 0 -1 0 -2.25

H20 + e − -> OH − + ½ H2

E0 = −0.828V

H2 + 2e − -> 2H−

E0 = −2.25V

H2O H2 H−

+1 0 -1 -0.828 -2.25Latimer-

Diagram

ΔG0 = −nFE

Frost-Diagram

acidic basic

6


Oxidation – Reductions Reactions

O2 H2O2 H2O0 -1 -2

0.695 1.763 Latimer-Diagram O2 H2O − OH−

0 -1 -2 −0.065 0.867

acidic basic


Hydrogen - Occurrence

H11

99.9855% 0.0145%

most abundant element in the universe

heavy water cosmic radiation inupper atmospheres

10-15 %

H12 H1

3

Protium H Deuterium D Tritium T

stable stableβ-decay: 32He + 0−1e

τ½ = 12.34 yrs 63Li + 10n -> 42He + 31H

7


Hydrogen – Physical Properties

101.51101.42100.00boiling point in 0C

4.493.820.00melting point in 0C

13.411.233.98T @ max. density in 0C

1.21501.10591.0000max. density of liquid water

1.21381.10440.99701density @ 25oC g/cm3

22.031520.027618.0150molecular weight

T2OD2OH2OProperties


Hydrogen – Chemical Properties

The hydride anion H−: strong reducing agent (E0 = −2.25 V)

& good ligand

(BH4−)3Al3+ [(en)2Li+]AlH4

− (Ph3P)ReH8

8

Ionic (salt-like) Hydrides: NaH, CsH, MgH2

ΔE.N.: 1.3 (CsH) – 1.0 (MgH2) × only 30 – 18% ionic characterionic radius (exp.: 1.39 – 1.14, calc.: 2.04 Å)

Metallic (interstitial) Hydride: PdH2, UH3electr. conductance: M—M and M—H “metallic bonding”

hydridic H: UH3 + 3H+ U3+ + 3H2protic H: cathod. H2-evolution from

electrolysis of PdH2

Covalent (molecular) Hydride: B2H6, CH4, NH3molecular structures: Gillespie & Nyholmformation of polymers, dimers, oligomers & complex structures

NaH

Pd sponge[Pd]—Hads

Diborane



• 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

9


The Alkaline-Metals – The Elements

Lithium (Li) Sodium (Na) Potassium (K)

Rubidium (Rb) Caesium (Cs) Francium (Fr)τ½ = 22 min

http://www.chemsoc.org/viselements/pages/pertable_fla.htm


The Alkaline-Metals – Physical Properties

10


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 H2S8 + 2e− -> S8

2−



11



[(15crown5)Rb]+Na −

inverse Na hydride

[(15crown5)Cs]+e −

an “electride”



J. L. Dye Acta Cryst. C (1990) 46, 1831

Bis(15crown5)cesium electride, space fill (left) and stick-model (right) with cell axis – Where is the electron?

electrontrappingcavity3.7 – 4.8 Å

large cationic complexes8 – 10 Å

alkalide counter-part structures

are known , e.g.:(15C5)2Cs+Na−

12


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 radiationproduces colored defects. The color of the defect dependson the nature of the host lattice (dimensions)

http://mrsec.wisc.edu/Edetc/cineplex/Fcenter/text.html


The Alkaline-Earths – The Elements

Beryllium (Be) Magnesium (Mg) Calcium (Ca)

Strontium (Sr) Barium (Ba) Radium (Ra)τ½ = 1600 yrs


13


The Alkaline-Earths – Physical Properties


The Alkaline-Earths – Chemical Properties

Mg + 2H+ -> Mg2+ + 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...)

14


The Group 13 Elements


Boron (B)

non-metal


Diborane (B2H6)convenient laboratory synthesis:@ RT3Na(BH4) + 4 Et2O • BF3-> 2B2H6 + 3NaBF4 + 4Et2O

industrial synthesis:@ 450K2BF3 + 6NaH -> B2H6 + 6NaF

B2H6 (ΔfH0 = +36 kJ/mol)air-moisture sensitiveexplodes with O2 (stable borates)very toxic

controlled pyrolysis of B2H6 via reactive BH3 intermediates & H2 form.

15


Boranes: Wade’s Rules

BnHn2− closo

BnHn+4 nido

BnHn+6 arachno

BnHn+8 hypho controlled pyrolysis of B2H6via reactive BH3 intermediates


B12 B11 B10 B9 B8 B7 B6 B5 B4

closo-

nido-

arachno-

B6H62-

B12H122-

IhOh

and bythe way…Al does it as well

16



Boron-Neutron Capture therapy (BNCT)

thermalneutron

selective cell-killing withslow neutrons

ionizing α-particlestravel one cell-diameter,very destructive

no hit-no harm

17


Bonding in Diborane (B2H6)



18





don’t forget about

B B

H

B B

B

H

…similar to

in higher borane clusters

19




Carbon (C)

non-metal




Nitrogen (N)

20




Oxygen (O)




Fluorine (F)

21




Helium (He)



Description :A colorless, odorless gas that is totally unreactive. It is extracted from natural gas wells, some of which contain gas that is 7% helium. It is used in deep sea diving for balloons and, as liquid helium , for low temperature research. The Earth’s atmosphere contains 5 parts per million by volume, totaling 400 million tons, but it is not worth extracting it from this source at present.

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 M.W. Travers in 1898 (London, UK)

Origin : Greek ‘neos’ (new)

Description :A colorless, odorless gas that comprises 18 parts per million of air. Neon will not react with any other substance. It is produced from liquid air for ornamental lighting (i.e. neon signs) because it glows red when an electrical discharge is passed through it.

Discovered : 1899 by Lord Rayleigh and Sir William Ramsay

Origin : Greek ‘argos’meaning inactive.

Description :The third most abundant gas, making up one percent of the atmos-phere. The quantity has increased since the Earth was formed because radioactive potassium turns into argon as it decays. Argon is a colorless, odorless gas that is totally inert to other substances, and for this reason it is ideal in light bulbs.

Discovered : by Sir William Ramsay and M.W. Travers in 1898

Origin : Greek ‘kryptos’, meaning hidden

Description :A colorless, odorless gas that is inert to everything but fluorine gas. The isotope krypton 86 has a line in its atomic spectrum that is now the standard measure of length : 1 meter is defined as exactly 1,650,763.73 wavelengths of this line. Krypton is one of the rarest gases in the Earth’s atmosphere, accounting for only 1 part per million by volume.

Discovered : by Sir William Ramsay and M.W. Travers in 1898

Origin : Greek ‘xenos’, meaning strange.

Description :A colorless, odorless gas that makes up 0.086 parts per million of the atmosphere. About half a ton a year is produced from liquid air and used for research purposes.

Documents

A Snapshot on Main Group Chemistry - inorganic chemistry 8a small.pdf · A Snapshot on Main Group Chemistry 8. Chemistry of the Main Group Elements s ix - c o o r d in a t e c a r