Inorganic Chemistry (Chemistry of Main Group Elements) PDF

Inorganic Chemistry (Chemistry of the main group elements) Chemistry Department, Faculty of Science, Tanta University  “The p-BLOCK ELEMENTS” Group III Elements 2 of 32 © Boardworks Ltd 2005  Group III, The Boron Family 3 of 32...

Inorganic Chemistry (Chemistry of the main group elements) Chemistry Department, Faculty of Science, Tanta University  “The p-BLOCK ELEMENTS” Group III Elements 2 of 32 © Boardworks Ltd 2005  Group III, The Boron Family 3 of 32 © Boardworks Ltd 2005  Group 13/III Elements (Boron Group) Elements Symb. Elec. Stru. Boron B [He]2s2,2p1 Aluminum Al [Ne]3s2,3p1 Gallium Ga [Ar]4s2,3d10, 4p1 Indium In [Kr]5s2,4d10,5p1 Thallium Tl [Xe]6s2, 4f14, 5d10, 6p1 4 of 32 © Boardworks Ltd 2005  “ General Properties ”1- Oxidation States Elements Elecectronic Structure Oxidation state B [He], 2s2, 2p1 III Al [Ne], 3s2, 3p1 III I Ga [Ar], 3d10, 4s2, 4p1 III I In [Kr], 4d10, 5s2, 5p1 III I Tl [Xe], 4f14,5d10,6s2, 6p1 III I More Stable Oxidation State Stability Stability Less Stable Oxidation State Decrease Increase 5 of 32 © Boardworks Ltd 2005  Stability of Oxidation States  Al always trivalent and may Elements Oxidation be form univalent, but state unstable. B III Al III I  The (+I) oxidation state of Ga and In compounds is less Ga III I stable than (+III). In III I  Thalous (+I) compounds Tl III I are more stable than thallic (+III) compounds. Decrease Increase 6 of 32 © Boardworks Ltd 2005  How and Why does monovalency occure?  How…? This explained by Inert Pair Effect. is the tendency of the electrons in the outermost atomic s orbital to remain unionized or unshared in compounds of post-transition metals. The s-electrons in the outer shell remaining paired and not participate in bonding.  Why….? This is because the energy required to ionize them exceeds the energy evolved when they forms bonds, then the s-electrons will remain paired. 7 of 32 © Boardworks Ltd 2005 Two major reasons for the inert-pair effect: 1.increasing ionization energies 2.decreasing bond strengths. Ionization energies increase because filled (n−1)d or (n−2)f subshells have poor shielding effect on ns orbitals. Thus the two electrons in the ns subshell undergo high effective nuclear charge, so they are strongly attracted to the nucleus, reducing their participation in bonding. therefore more difficult to remove these ns2 electrons. Because Tl is less likely than Al to lose its two ns2 electrons, its most common oxidation state is +1 rather than +3 8 of 32 © Boardworks Ltd 2005  The oxidation state ( +II ) GaCl2, However, Ga is not really divalent….? The structure of GaCl2 has been shown to be Ga+[GaCl4]-, which contain (+I) and (+III). 9 of 32 © Boardworks Ltd 2005  2- Type of Bonds  Small size of (+III) ions and their III highly charges, favors the formation of covalent compounds. III I  The (+I) ions are much larger, with III I low charge, favors the formation of ionic compounds. III I  B, is the smallest element and more electronegative than others, it is III I always covalent. 10 of 32 © Boardworks Ltd 2005  Al, Ga, In and Tl simple compounds  (GaCl3, AlCl3,…) are covalent when anhydrous. But, in solution become ionic with acidic character…?  1- Ionic Character: M atom s p d M3+ ion s p d s p d sp3d2 M3+ ion having gained 6 lone pairs from 6 oxygen atoms of 6 H2O 11 of 32 © Boardworks Ltd 2005   Forming the hydrated complex increases the effective size of the M3+ ion, thus spreading the charge over a large area, according to Fajan’s rule stable ionic salts are formed.  2- Acidic Character: H H2O + [ (H2O)5 M O ]3+ [M (H2O)5(OH)]2++ H3O+ H  The bond between M and O is strong bond, the strength of this bond weakens the O-H bonds, hence there is a tendency to lose protons. 12 of 32 © Boardworks Ltd 2005  3. Size of atoms  Do not increase in a completely regular way from B to Tl  The size increases largely from B to Covalent radius (ang) 2 Al and from Ga to In due to the added extra shell of electrons. 1.6 1.2  The size increases by very small amount from Al to In due to the added 0.8 filled d orbital that have small shielding effect for the nucleus 0.4 B Al Ga In Tl (d-block contraction). Similarly, the size increases by very small amount from In to Tl due to the added filled f orbital that have very small shielding effect for the nucleus ( f-block or lanthanide contraction).  Note: the shielding effects decrease in the order: s>p>d>f 13 of 32 © Boardworks Ltd 2005  General properties 4. Metallic properties:  B is metalloid, hard, and dark semiconductor solid.  Al, Ga, In, and Tl are fairly reactive metals and have a silver luster.  Melting points: Al (660 oC), Ga (30 oC, unusual structure which contains Ga2 units ), In (157 oC), and Tl (303 oC). 14 of 32 © Boardworks Ltd 2005  Compounds of Boron with Oxygen  Oxides  oxo compounds of boron  The most important compounds of boron.  B is strong oxophiles (high affinity for oxygen). Examples of compounds are boric acid, polyborate salts, boron sesquioxide, and borosilicate glasses.  Sesqui- = one and half  The oxides of boron have formula MO1.5 or M2O3. 15 of 32 © Boardworks Ltd 2005  1- Oxides “Boron Sesquioxides and Borates” Boron Sesquioxides (B2O3) Preparation  By heating the element in oxygen.  4B + 3O2 2B2O3  By dehydrating the boric acid. 100 oC Red hot B O 2H3BO3 z 2HBO 2 2 3 Orthoboric Acid Metaoboric Acid  Rapid cooling of molten B2O3 forms borate glasses (have technological significance). 16 of 32 © Boardworks Ltd 2005  Boron Sesquioxides B2O3  Weakly Acidic oxide Properties Amphoteric character  B2O3 is the anhydride form of orthoboric acid. It is nonmetallic oxide and has acidic properties. B2O3 + 3MgO Mg3(BO3) 2 Acidic Strong Orthoborates Basic “salts”  But, when reacts with strongly acidic oxide, it behaves as a basic oxide. B2O3 + P2O5 2BPO4 Basic Strong Boron Phosphate acidic 17 of 32 © Boardworks Ltd 2005   B2O3 is weakly acidic oxide B2O3 +H2O →H3BO3  Al2O3 is amphoteric Al2O3 + NaOH → NaAlO2 +H2O Al2O3 + HCl → AlCl3 +H2O  Tl2O is strong basic oxide Tl2O + H2O → 2Tl(OH) Basicity increase down the group 18 of 32 © Boardworks Ltd 2005  2- Oxo compounds of boron “Borates, Boric acid and boron silicate glasses”  Each boron atom is bonded to three oxygen atoms arranged at the corners of an equilateral triangle. B -atom 2s 2p B -atom in excited state 2s 2p Sp2-hybridization B -atom in BO3 2s 2p 3 bonds with 3 oxygen atoms 19 of 32 © Boardworks Ltd 2005  3- O B O O Simple Borates 20 of 32 © Boardworks Ltd 2005  3- O Orthoborates: Contains discrete BO33- ions. B Example: Mg3(BO3)2 O O 21 of 32 © Boardworks Ltd 2005   Simple unites of BO3 join together to form a variety of polymeric Open chain and ring structures. O O O B B B O O O O O O B B B Open Chain O O O O 22 of 32 Ring structure © Boardworks Ltd 2005  O- B O O B B - - O O O [B3 O6]3- 23 of 32 © Boardworks Ltd 2005   The solid orthoboric acid contains triangular B(OH)3 units which are bonded together through hydrogen bond into two dimensional sheets with hexagonal symmetry. The unit cell of boric acid 24 of 32 © Boardworks Ltd 2005  H H H O O H H H B O O O B B H H H O O H O O H H H H H O O O O H B H H B O The unit cell O O of orthoboric acid H B H H H O O H H Orthoboric Acid 25 of 32 © Boardworks Ltd 2005  Properties  Very weak monobasic acid  Orthoboric acid H3BO3 = B (OH)3  It is soluble in water and behaves as a weak monobasic acid. It does not donate protons like most acids BrØnsted acid, but it accept OH- (Lewis acid, electron-pair acceptor). B(OH)3+2H2O [B(OH)4]- + H3O+ pKa = 9.2 H H O O B B HO OH HO OH O H Plane Triangle Tetrahedral borate anion 26 of 32 © Boardworks Ltd 2005  Becomes strong monobasic acid by addition of cis dihydroxy compounds such as glycerol, or sugars that remove [B(OH)4]- from solution and shifts the equilibrium to the right, hence all the H3BO3 ionizes and the maximum number of H+ are produced. HO -  At high concentrations: B O OH O B Polymeric metaborate OH species are formed. HO B O Polymeric metaborate species 3B(OH)3 [B3O3(OH)4]- + H3O+ Boric acid (B(OH)3 _ _ HO OH HO OH OH HO B B B O O OH HO OH B B HO O OH Boric acid Borate anion Triborate anion   Made up from fusion of sodium borate Na3BO3 with silica  Low thermal expansion (little tendency to crack when heated or cooled)  Example is Pyrex glass. Used for cooking- and laboratory-ware 29 of 32 © Boardworks Ltd 2005  Compounds of Aluminum with Oxygen  Aluminum has a very strong affinity for oxygen, and the reaction is strongly exothermic “Thermite Reaction ” 2Al + 3/2O2 Al2O3  = 1700 KJ mol -1  The very strong affinity of Al for oxygen is used in the metallurgicall extraction of other metals from their oxides. 8Al + 3Mn3O4 4Al2O3 +9Mn 2Al + Cr2O3 Al2O3 +2Cr 30 of 32 © Boardworks Ltd 2005  3- hydrides “Boron Hydrides or Boranes” None of gp.III react directly with hydrogen  Reaction occurs in the presence of reducing agent. Boron forms interesting hydrides called Boranes. There are almost 20 boranes into 3 series 31 of 32 © Boardworks Ltd 2005  Properties  Electron-deficient, Colorless  Diamagnetic, Gases (B2 and B4 hydrides)  Volatile liquids (B5 and B6 hydrides)  Sublimable solid B10H14  Burn with a characteristic green flame  Several of them ignite explosively on contact with air 32 of 32 © Boardworks Ltd 2005  ***Diborane B2H6 B –atom in ground state 2s 2p B -atom in excited state 2s 2p H H H Sp3-hybridization B B 2s 2p H H H 2covalent bonds Overlape with1s-orbital with 2H-atoms of H-atoms 33 of 32 © Boardworks Ltd 2005  Structure Of Diborane, B2H6 H H H B B H H H 34 of 32 © Boardworks Ltd 2005  Preparation of Diborane  Mg3B2 + H3PO4 Mixture of boranes B2H6 180oC 2BF3 + 6NaH B2H6 + 6NaF 4BCl3 + 3Li(AlH4) 2B2H6 + 3AlCl3 35 of 32 © Boardworks Ltd 2005  Reactions of Diborane 1-With Oxygen Diborane gas (pyrophoric gas: substances that ignite instantly upon exposure to oxygen) reacts spontaneously with air, often with explosive violence and a green flash. B2H6(g) + 3O2(g) 2B(OH)3(s) 2-With Water Diborane is readily hydrolyzed by water or aqueous alkali: B2H6 + 6 H2O 2B(OH)3(aq) + 6H2 36 of 32 © Boardworks Ltd 2005  3-With Ammonia (1200  C) 3B2H6 + 6NH3 2B3N3H6 + 12H2 (200  C)  _ + NH3 H H H H B B + 2NH3 B B H H H H NH3 H H H H B2H6.2NH3 B3N3H6 or (H3B3N3H3) Borazine (Inorganic Benzene) 38 of 32 © Boardworks Ltd 2005  *** - Tetrahydroborate ion [BH ] 4  Examples are alkali metal hydride H H B Preparation H H  2NaH + B2H6  2Na[BH4] Properties  White ionic solids.  Tetrahedral.  Reducing agents.  Li [BH4] reacts violently with water.  Na[BH4] slightly decompose in water.  K[BH4] is quit stable. 39 of 32 © Boardworks Ltd 2005 Hydrides of other group III elements  AlH3 exists as solid but is not readily available.  (AlH3)n exists as a white polymer with hydrogen bridges like diborane.  LiAlH4 (Lithium tetrahydroaluminate) Pure Ga2H6 has been prepared in 1994. LiGaH4 (lithium tetrahydrogallate)  Hydrides are very unstable.  Comparison between [BH4]- and [AlH4]- *** [BH4]- [AlH4]- Reducing agent More powerful reducing agent because B is more Can be used in electronegative than Al aqueous solutions Can not be used in aqueous because boron dose solutions because Al has 3d not have d orbital orbital in the third shell in the second shell thus can be easily so it is not hydrolyzed by water. hydrolyzed.  4- Nitrides “Boron nitride (B3N3) BN ” Preparation 1200 B2H6 + 2NH3 2BN + 3 H2O 1200 B2O3 + 2NH3 2BN + 3 H2O 42 of 32 © Boardworks Ltd 2005  “Boron nitride (BN) ” (Graphite and diamond analogous)  Planar sheets (like graphite) of alternating B and N atoms in hexagonal rings.  Slippery material (oily) when dissolved that is used as lubricant. Colorless, electrical insulator. Layered BN changes into a denser cubic phase at high pressures and temperatures. Hard crystalline (like diamond but with lower hardness). 43 of 32 © Boardworks Ltd 2005  5- Halides Trihalides Dihalides Monohalides 44 of 32 © Boardworks Ltd 2005  1- Trihalides B, forms covalent trihalides BX3. Preparation 2B + 3X2  2BX3 ( X = F, Cl, or Br)  Rapidly hydrolyzed by water: BCl3 + 3H2O  B(OH)3 + 3HCl  Al, Ga, In, Tl, form covalent trihalides (Cl, Br, I)  Al, Ga, In, Tl, form ionic trifluorides. Due to the higher electronegativity of Fluore. 45 of 32 © Boardworks Ltd 2005  Trihalides of boron Structure of BF3 5 2 2 1 B: 1s , 2s ,2p 2p 5 B atom in ground state: 2s 2p 5 B atom in excited state: 2s 2p sp2 Hybridization: sp2 sp2 sp2 2p Hybridized B atom in BF3 sp2 sp2 sp2 46 of 32 © Boardworks Ltd 2005  Empty 2pz orbital on B- atom accept a lone pair of electron from any F- atom, forming dative  sp2 sp2 sp2 bond, to obtain an octet shell. F F F B B B F F F F F F 47 of 32 © Boardworks Ltd 2005  Lewis acidity of BX3  Due to the presence of an empty orbital, the B atom in the BX3 molecule can readily accept a lone pair of electrons from a donor atom such as O, N, P or S and serve as a Lewis acids. F B F F F 48 of 32 © Boardworks Ltd 2005  The order of the Lewis acid strengths of BX3 BF3 < BCl3 < BBr3  In contrast to the order of the electronegativity of the attached halogens.  This trend stems from the greater -bonding (X:→B) in the order: F > Cl > Br giving rise to the partial occupation of the p-orbital on the B atom by electrons donated by the halogen atoms. 49 of 32 © Boardworks Ltd 2005  - 2- Formation of BF4 a- Formation of BF3 5 2 2 1 B: 1s , 2s ,2p 2p 5 B atom in ground state: 2s 2p 5 B atom in excited state: 2s 2p sp2 Hybridization: sp2 sp2 sp2 2p Hybridized B atom in BF3 sp2 sp2 sp2 50 of 32 © Boardworks Ltd 2005  - b- Formation of BF4 2p Hybridized B atom F in BF3 sp2 sp2 sp2 sp3Hybridization: B sp3 sp3 sp3 sp3 F F Hybridized B atom F - 3 3 3 3 in BF4 sp sp sp sp 51 of 32 © Boardworks Ltd 2005  “ Covalent Trihalides of other group III elements ”  Al, Ga, In, Tl, form covalent dimeric trihalides (Cl, Br, I) in anhydrous form to attain an octet of electrons. Cl Cl Cl Al Al Cl Cl Cl  When the halides is dissolved in water, because of the high heat of hydration which is sufficient to break the covalent dimer, the covalent dimmer is broken into [M(H2O)6]3+ and 3X- ions. 52 of 32 © Boardworks Ltd 2005  2- Dihalides  Boron forms halides of formula B2X4. These compounds decompose slowly at room temperature. B2Cl4 can be made as follow: electric discharge 2BCl3 + 2Hg B2Cl4 + Hg2Cl2 low pressure The structure is: In the gaseous and liquid states In the solid state Because of free rotation about the B-B bond Because of crystal forces 53 of 32 © Boardworks Ltd 2005  Dihalides of other group III elements  Ga, In, and Th form dihalides. 2GaX3 + Ga  3GaX2 (X = Cl, Br, or I)  The formula GaCl2 is more properly written as Ga+[GaCl4]- that contains: Ga(I) and Ga(III) rather than Ga(II). 54 of 32 © Boardworks Ltd 2005  3- Monoihalides  Boron forms a number of stable polymeric monohalides (BX)n:  B4Cl4 is a pale yellow solid and the four boron atoms form a tetrahedron. 55 of 32 © Boardworks Ltd 2005  Monohalides of other group III elements  The other Group III elements will all form monohalides MX containing metals with +1 oxidation state. Oxidation state +1 increases in stability down the group. 56 of 32 © Boardworks Ltd 2005  Problems a. What is the most common oxidation state for Boron and Thallium? Rationalize your answer? Comment on the tendency of TlCl for disproportionation? b. Why does the size of group 3 atoms not increase in a regular way? c. Write sort notes on Pyrex glass and structure of diborane? d. Compare between [BH4]- and [AlH4]- in regards to the reducing properties and the medium of usage? e. Explain the principle of using group 3 halides as Lewis acids and arrange the halides of boron (BF3, BCl3, BBr3) according to their Lewis acidity? Rationalize your answer? f. Write short notes about boron nitride and Borazine? 57 of 32 © Boardworks Ltd 2005