Atomic Radii of Some Representative Elements (in Picometers)

Transcription

1 Atomic Radii of Some Representative Elements (in Picometers)

2 Group 3A, Group 13 B, Al, Ga, In, and Tl; Valence-shell electron configuration: ns 2 np 1 Group 3A elements show increasing metallic character going down the group. Boron: a metalloid, forms covalent network solid, and highest melting point in the group

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4 Some Physical Properties, Sources, and Methods of Preparation

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6 Some Important Reactions

7 Properties of Boron (1s 2 2s 2 2p 1 ) A metalloid; forms covalent network solid; highest melting point in the group, and the least reactive All boron compounds are covalent molecules; Boron molecules, such as BF 3, have incomplete octet and acts as Lewis acid, example: BF 3 + :NH 3 F 3 B:NH 3 Boron hydrides acquire octet by forming H- bridges, electron-deficit bonds; Boron oxide, B 2 O 3, forms weak boric acid, B(OH) 3 ; icosahedron

8 3 LiAlH 4 ( et) + 4 BF 3 ( et) 2 B 2 H 6 ( g) + 3 LiAlF 4 ( et) pyrolysis Boranes - Wade rules Lewis acids

9 Borides - binary compounds with less electronegative elements - variable composition (M 5 B, M 4 B, M 3 B, M 2 B, MB, M 7 B 3, M 10 B 11, MB 66 e.t.c.) - Very hard, chemically inert, high electric conductivity - Direct synthesis at high temperature: CaB 6 MgB 2 superconductor at 38 K

10 Superhard materials: Selected applications Boron nitride BN isoelectronic with C cubic lattice as diamond Boron carbide ceramics - approximately B 4 C 2 B 2 O C B 4 C + 6 CO Boronated metals hard coating Others: BN nanotubes isolectronic with C-nanotubes Elemental boron fiber light, high-strength - aerospace (composite) structures

11 Aluminum Electron configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 or [Ar] 3s 2 3p 1 Third most abundant element (and most abundant metal) in the Earth s crust; Most important metal of Group 3A;

12 Aluminum Production Extracted from bauxite, Al 2 O 3 nh 2 O; Produced by the Hall-Heroult process - electrolysis of molten Al 2 O 3 -Na 3 AlF 6 (cryolite) mixture at ~ 960 o C Aluminum production is an energy intensive process Energy consumption: ~ 54 MJ/kg Al (~3% of electrical energy supply) Re-cycling saves up to 95% of this energy; (Re-cycle an aluminum can and power your desk-top monitor up to 3 hours)

13 Importance of Aluminum Lightweight metal (density = 2.70 g/cm 3 ); Forms strong, lightweight alloys with copper and magnesium for aircraft bodies and parts; High resistance to corrosion - extensively used to make beverage containers (soda drinks cans);

14 Chemical Properties of Aluminum Reactive metal, readily oxidized by atmospheric O 2 to form Al 2 O 3 ; Al 2 O 3 forms protective coating (an anodic protection) that prevents further corrosion of the metal; Al 2 O 3 is amphoteric - reacts with both strong acids & bases; Aluminum reacts with halogens to form AlX 3 ; Al 2 O 3 and AlF 3 are strictly ionic compounds; Other halides are ionic with covalent characteristics.

15 Reactions of Aluminum With strong acids: 2Al(s) + 6 HCl(aq) 2AlCl 3 (aq) + 3H 2 (g); 2Al(s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + 3H 2 (g); 2Al(s) + 2HNO 3 (aq) Al 2 O 3 (s) + 2NO(g) + H 2 O(l) (The third reaction does not occur completely because the oxide forms protective coating to prevent further reaction.) With a strong base: 2Al(s) + 6H 2 O(l) + 2NaOH(aq) 2NaAl(OH) 4 (aq) + 3H 2 (aq);

16 Important Compounds of Aluminum Al 2 O 3 source of aluminum metal and forms protective coating to the metal to prevent corrosion; Al 2 (SO 4 ) 3 most important industrial compound; 1. use in municipal water treatment plants; 2. Prepared by reaction of H 2 SO 4 with Al 2 O 3 or Al(OH) 3 : Al 2 O 3 (s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (s) + 3H 2 O(l) 2Al(OH) 3 (s) + 3H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (s) + 6H 2 O(l)

17 Exercise #5 1. Classify the following oxides as acidic, basic or amphoteric. B 2 O 3 Al 2 O 3 In 2 O 3 Balance the following equations: 1. B(s) + HNO 3 (aq) B 2 O 3 (s) + NO(g) + H 2 O 2. Al(s) + H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + H 2 (g) 3. Al 2 O 3 (s) + HCl(aq) AlCl 3 (aq) + H 2 O(l)

18 Group 4A, Group 14 (vs: ns 2 np 2 ) Contains: a nonmetal (C), two metalloids (Si & Ge), and two metals (Sn & Pb); Carbon exists in 3 allotropic forms: graphite, diamond, and the bucky-ball. Graphite has sp 2 hybridization; Graphite is soft and conduct electric current; Diamond contains sp 3 hybridization and forms covalent network solids; does not conduct electricity; Diamond is the hardest material on Earth.

19 Group 4A, Group 14

20 Some Physical Properties, Sources, and Methods of Preparation

21 Some Important Reactions

22 Carbon: 1s 2 2s 2 2p 2 Most important element on Earth forms the basic skeletal structures of all living things; Carbon forms strong covalent bonds with many elements and with itself; Carbon forms sp, sp 2, and sp 3 hybridizations; In sp hybridization, each carbon forms 2 σ- and 2 π- bonds; example in H C C H In sp 2, each carbon forms 3 σ- and a π- bonds; In sp 3 hybridization each carbon forms 4 σ-bonds;

23 Important Compounds of Carbon CO toxic gas (binds to hemoglobin); forms during combustion of carbon in limited oxygen supply; used in methanol production. CO 2 end-product of combustion of carbon or carbon-containing compounds; greenhouse gas that keeps Earth temperature relatively warm; CO 2 is essential to life used by plants in photosynthesis; NaHCO 3 used as baking soda for cooking and as in fire-extinguishers; Na 2 CO 3 used in glass manufacture; CaCO 3 used in steel production;

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25 Methane clathrates - CH 4 in the ice crystal structure - melting of 1 m 3 clathrates releases 164 m 3 of CH 4

26 Carbonyl halogenides - Planar important for chemical synthesis - phosgene - Very toxic chemical weapon CO(g) + Cl 2 (g) Cl 2 CO(g)

27 Other Important Compounds of Carbon Pseudohalogenides derived from: HCN hydrogen cyanide, HCNO fulminic acid, HNCO isocyanic acid, HNCS isothiocyanic acid and H 2 NCN cyanamide. Carbides: M x C y with M being less electronegative - ionic: either as C IV (carbides), (C 2 ) 2 (acetylides), (HC 2 ) (hydrogenacetylides) - CaC 2 ; CaO with carbon at 2200 C: - Covalent - Hard, chemically inert, high m.p. - SiC, B 4 C - Metalic Interstitial compounds atoms of C occupy the octahedral cavities in the crystal structures of metals (e.g. TiC, ZrC, VC, NbC, V 2 C, MoC, Mo 2 C, WC...) - high m.p. ( C), hardness, electric conductivity - Transition carbides between ionic and metalic carbides (e.g. Cr 2 C 3, Mn 3 C, Fe 3 C, Co 3 C...)

28 Chemistry of Silicon Silicon - a metalloid; a covalent network solid with diamond-like structure; very important in the electronic industries - forms semi-conductors. Silicon dioxide or silica (SiO 2 ) - the second most abundant substance on the Earth s crust; also the source of silicon many polymorphs; SiO 2 - used in the manufacture of glass and ceramics; Silicon carbide (SiC) has diamond-like structure; used to make abrasive and heat resistant ceramics.

29 Production of Silicon SiO 2 (s) + 2C(s) Si(s) + 2CO(g); Si(s) + 2Cl 2 (g) SiCl 4 (g); SiCl 4 (g) + 2Mg(s) Si(s) + 2MgCl 2 (s); Final purification done by zone-refining Silanes: structures similar to hydrocarbons, polymers Siloxanes: polymer, silicon oil, rubber

30 Silicon dioxide many polymorphs α-cristobalite tridimite β-quartz melanophlogite stishovitee

31 Silicates some can be derived from H 4 SiO 4 Island silicates α-ca 2 SiO 4 Be 3 Al 2 Si 6 O 18 - beryl in cement hemimorfit Zn 4 (OH) 2 Si 2 O 7 chain silicates asbestos

32 Layer silicates and aluminosilicates Clay minerals caolinite

33 3-dimensional aluminosilicates Zeolites - absrobents, molecular sieve, ion-exchange Na 2 Al 2 Si 3 O 10 2H 2 O

34 Germanium Usually as admixtures in other minerals and in some coal ashes transistors Halogenides non-volatile

35 Tin and Lead Both are soft metals; T m ( o C): Sn (232) & Pb (327) Tin - used mainly in tin-plating for making food cans, for making solders, bronze, and pewters; Lead - mainly used to make automobile batteries; some are used as lead shots and radiation shields; Both metals form +2 and +4 oxidation states; Reacts with O 2 SnO, SnO 2, PbO & PbO 2 ; Reacts with Cl 2 SnCl 2, SnCl 4, PbCl 2 & PbCl 4 ; SnO, PbO, SnCl 2, and PbCl 2 are ionic; SnO 2, PbO 2, SnCl 4, and PbCl 4 are molecular;

36 Important Compounds of Tin and Lead SnCl 2 used as reducing agent, tin plating, catalyst; SnF 2 additive in toothpaste to prevent cavity; PbO used in ceramic glaze, and cement; PbO 2 oxidizing agent and battery electrodes; PbCrO 4 for making yellow pigment for paint;