Chapter 12,13

He Ne Ar Kr Xe Rn The Periodic Table of the Elements CrMnFeCoNi Mo W Tc Re Ru Os Rh Ir Pd Pt Most Probable Oxidation State _ H Li Na K Rb Cs Fr Sc Y Be Mg Ca Sr Ba Ra La Ac B Al Ga In Tl Ti Rf Hf Zr C Si Ge Sn Pb F Cl Br I At O S Se Te Po N P As Sb Bi Zn Cd Hg Cu Ag Au +5 V Nb Ta Ce Th PrNdPmSmEuGdTbDyHoErTmYbLu PaUNpPuAmCmBkCfEsFmMdNoLr +3 DuSgBoHaMe

 Boron:  In nature it is found as Borates:  Ulexite : {NaCa[B 5 O 6 (OH) 6 ].5 H 2 0}  Borax : {Na 2 [B (OH) 4 ]. 8 H 2 0}  Colemanite: {Ca 2 [B (OH) 3 ] 2.2 H 2 0)}  Kernite: {Na 2 [B 4 O 5 (OH) 4 ].2 H 2 0}  Borates do have complex structures, but common to all is that Boron is contained as trigonal BO 3 or tetragonal BO 4 units.

 The cations in these minerals are typically alkali or alkaline earth cations.  The largest source of Boron is in the form of Borax found in the mojave desert in california  No ionic compounds involving simple B 3 + cations are formed because the ionization enthalpies for boron are so high that lattice energies or hydration enthalpies cannot offset the energy required for formation of a cation.

 Boron is sp2 hybridized in trigonal planes.  All BX3 planes compounds are strong lewis acids  interaction with Lewis bases (molecules or ions) gives tetrahedral adducts such as BF3.O(C 2 H 5 ) 2,BF 4 -, and B(C 6 H 5 ) - 4. The formation of such Lewis acid-base adducts requires a change to Sp3 hybridization for boron. 

 Isolation of the element:  Boron is made in 95-98% purity as an amorphous powder by reduction of the oxide B with Mg  Or Zn

 Borosilicate glass- pyrex  Detergents  Flame retardants  Ceramics  Pyrotechnics  Used in production of impact resistant steels  Control rods in nuclear reactors

 2c-2e - B-H  3c-2e - B-H-B  2c-2e - B-B  3c-2e - B-B-B

Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry: principles of structure and reactivity, 4th ed. New York: HarperCollins College Publisher,

Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry: principles of structure and reactivity, 4th ed. New York: HarperCollins College Publisher,

Housecroft, C. E.; Sharpe, A. G. inorganic Chemistry. New York: Pearson Education Limited,  - rhombohdral  rhombohedral, B 12 (B 12 ) 12, (B 12 )(B 12 )(B 60 )

Housecroft, C. E.; Sharpe, A. G. inorganic Chemistry. New York: Pearson Education Limited,

 The structure of Boranes:

 The hydrides of Boron:  Diborane:  Lab quantities:  Industrial Quantities:

 Reactions of Boranes:

 Deca boranes:

 Borohydrides of many metals have been made and some representative syntheses are:

Housecroft, C. E.; Sharpe, A. G. inorganic Chemistry. New York: Pearson Education Limited,

Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry:principles of structure and reactivity, 4 th ed. New York: HarperCollins College Publishing,

 n = number of B atoms in parent closo - deltahedron  Always n+1 bonding e - pairs and n+1 bonding MOs  nido has n-1 vertices  arachno has n-2 vertices  hypho has n-3 vertices

 Find total available bonding e - s:  Each B-H unit gives 2 e - s  Each additional H gives 1 e -  Overall charge  Find parent closo -deltahedron  n+1 bonding e - pairs  Is it closo, nido, arachno, hypho ?  Lose highest connectivity B first then lose adjacent sites  Determine number of remaining hydrogen atoms  Each vertex has a H  “sew up” hole with H atoms  Bridging H atoms  Low connectivity B atoms can get another 2c-2e - B-H bond  Try to keep it as symmetrical as possible

Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry: principles of structure and reactivity, 4th ed. New York: HarperCollins College Publisher,

 10 B has large cross-section for neutron capture  10 B +   + 7 Li  Products can kill cells  Cancer treatment  Cages - need high [ 10 B] in cell

 The main resemblances to silicon and differences from the more metallic aluminum are as follows:  1. The oxide B20 3 and B(OHh are acidic. The compound Al(OH)3 is a basic hydroxide, although it shows weak amphoteric properties by dissolving in strong NaOH.  2. Borates and silicates are built on similar structural principles with sharing of oxygen atoms so that complicated chain, ring, or other structures result.

 3. The halides of Band Si (except BF 3 ) are readily hydrolyzed. The AI halides are solids and only partly hydrolyzed by water. All act as Lewis acids.  4. The hydrides of B and Si are volatile, spontaneously flammable, and readily hydrolyzed. Aluminum hydride is a polymer, (AlH 3 ) n

 Crystalline boron is very inert and is attacked only by hot concentrated oxidizing agents. Amorphous boron is more reactive. With ammonia for instance, amorphous boron at white heat gives (BN) x a slippery white solid with a layer structure resembling that of graphite, but with hexagonal rings of alternating B and N atoms.

 Hydrated borates contain polyoxo anions in the crystal, with the following important structural features: 1. Both B0 3 and tetrahedral B0 4 groups are present, the number of B0 4 units being equal to the charge on the anion. 2. Anions that do not have B0 4 groups, such as metaborate, B , or metaboric acid, B (OH) 3, hydrate rapidly and lose their original structures. 3. Certain discrete as well as chain-polymer borate anions can be formed by the linking of two or more rings by shared tetrahedral boron atoms.

 Boric acid:  The acid B(OH) 3 can be obtained as white needles either from borates, or by hydrolysis of boron trihalides.  When heated, boric acid loses water stepwise to form one of three forms of metaboric acid, HB0 2. If B(OH) 3 is heated below 130°C, the so-called form- III is obtained, which has a layer structure in which B rings are joined by hydrogen bonding. On continued heating of form-III of HB0 2, between 130 and 150°C, HB0 2 -II is formed.

 Halides:  Boron trihalide is a gas (bp -101 deg C)  Boron trihalides are the strongest lewis acids.  They react with Lewis bases  B-X bonds are somewhat shorter than is expected from the sum of the single-bond covalent radii. This suggests a delocalized π - bond system

 Al is the most common of the elements  It is produced in pure form by electrolysis, and is the most dirty of the industrial processes.  Costs a lot of energy.  Main source is Bauxite, a hydrous Al –oxide  Al is attacked by diluted acids, but passivated by strong acids.  Al oxides are used to protect metals (anodized)

 They are made from their salts by electrolysis.  Ga is used mainly in semiconductors with Group V elements. (GaAs).  Tl is a trace element and is very toxic.  Main use to get rid of spies.

 Al has only one oxide formed Al 2 O 3  There is an alpha and a gamma oxide.  Difference is the process and the temperature to get alpha or gamma oxide.  Mixed Al oxides are ruby (Cr 3+ )and sapphire  (Fe 2+,Fe 3+, Ti 4+ )

 Halides are formed of all elements, the only one that is special is TlI3.  Tl and I2 form rather a Tl 1+ and I 3 - compound  All halides readily dissolve in benzene

 The most important hydride is LiAlH4  It is a strong reducing agent and is mainly used in organic chemistry  It is used e.g. to hydrate double bonds

 1. Boron  (a) Forms no simple B 3 +cation.  (b) Forms covalent compounds almost exclusively, and all polyatomic ions have covalent bonds.  (c) Obeys the octet rule, the maximum covalence being four.  (d) Forms trivalent compounds that readily serve as Lewis acids.

 (e) Frequently forms polyhedral structures: boranes and borates.  (f) Forms an oxide, B 2 0 3, and a hydroxide, B(OH) 3 both of which are acidic.  (g) Forms covalent halides that are readily hydrolyzed.  (h) Forms numerous covalent hydrides, all of which are volatile, flammable, and readily hydrolyzed.  (i) Forms a stable and important hydride anion, BH 4 -.

 2. Aluminum  (a) Readily forms an important 3+ ion, because it is electropositive.  (b) Is much more metallic than boron, and forms a greater number and variety of ionic substances.  (c) Forms both molecular and ionic substances, with coordination numbers of six and higher.  (d) Forms two oxides, only one of which is acidic.  (e) Forms a hydroxide that is weakly amphoteric, although mostly basic.  (f) Forms solid halides that are only partially hydrolyzable.  (g) Forms a polymeric hydride.  (h) Forms an anionic hydride (AlR - ) that is more reactive than BH 4 -.

 3. Gallium, Indium, and Thallium  (a) Readily give the M 3 + ion in solution, and have a rich coordination chemistry typical of metals.  (b) Form increasingly stable lower valent compounds, especially TI +.  (c) Increasinglyformweakercovalent bondsondeseentofthegroup,enhancing the formation of monovalent compounds.  (d) Form MX 3 halides that are increasingly aggregated in the solid state (through halide ion bridges) to give coordination numbers of four, six, and higher.  (e) Do not form important EH 4 - anions, except perhaps GaH 4 -.