Some Physical Properties, Sources, and Methods of Preparation

Transcription

1 Group 15, 5A Valence-shell configuration: ns 2 np 3 Exhibits varied chemical properties. 1. N and P are nonmetals; 2. As and Sb are metalloids; 3. Bi is a metal (the heaviest non-radioactive element)

2 Some Physical Properties, Sources, and Methods of Preparation

3 Oxides of Group 5A Elements Nitrogen: N 2 O, NO, N 2 O 3, NO 2, N 2 O 4, N 2 O 5 ; Phosphorus: P 4 O 6 & P 4 O 10 ; Arsenic: As 2 O 3 (As 4 O 6 ) & As 2 O 5 ; Antimony: Sb 2 O 3 & Sb 2 O 5 Bismuth: Bi 2 O 3 & Bi 2 O 5 phosphorus in orange, oxygen in red

4 Chlorides of Group 5A Elements Nitrogen: only NCl 3 ; Phosphorus: PCl 3 and PCl 5 ; Arsenic: AsCl 3 and AsCl 5 ; Antimony: SbCl 3 and SbCl 5 ; Bismuth: BiCl 3 All are molecular compounds.

5 Reactions of Oxides and Chlorides 3NO 2 (g) + H 2 O(l) 2HNO 3 (aq) + NO(g); N 2 O 5 (g) + H 2 O(l) 2HNO 3 (aq) P 4 O 10 (s) + 6H 2 O(l) 4H 3 PO 4 (aq); As 2 O 5 (s) + 3H 2 O(l) 2H 3 AsO 4 (aq); PCl 5 (s) + 4H 2 O(l) H 3 PO 4 (aq) + 5HCl(aq); AsCl 5 (s) + 4H 2 O(l) H 3 AsO 4 (aq) + 5HCl(aq); 2SbCl 5 (s) + 5H 2 O(l) Sb 2 O 5 (s) + 10HCl(aq);

6 The Chemistry of Nitrogen The triple bonds (N N) in N 2 provide high stability to the molecule; Oxidation states from -3 to 5 NH 2 OH (-1), N 2 H 4 (-2), and NH 3 (-3) Many reactions involving nitrogen gas are endothermic and compounds containing nitrogen decompose exothermically to the elements. N 2 (g) + O 2 (g) 2NO(g) ΔH = 180 kj 2NO 2 (g) N 2 (g) + O 2 (g); ΔH = -68 kj N 2 H 4 (g) N 2 (g) + 2H 2 (g); ΔH = -95 kj

7 Nitrogen Fixation The process of transforming N 2 to other nitrogen containing compounds. Atmospheric fixation (occurs naturally during thunderstorm): N 2 (g) + O 2 (g) 2NO(g); ΔH o = 180 kj 2NO(g) + O 2 (g) 2NO 2 (g); ΔH o = -112 kj 3NO 2 (g) + H 2 O(l) 2HNO 3 (aq) + NO(g); ΔH o = -140 kj

8 Biological Nitrogen Fixation Fixation of atmospheric N 2 by bacteria living in soils and water; some live in root nodules; Plants such as legumes and alfalfa have root nodules that contain nitrogen-fixing bacteria they benefit directly from these bacteria; Other plants benefit when the bacteria die and release absorbable forms of nitrogen (NH 3, NH 4 +, and NO 3 - ) to the soils;

9 Biological Nitrogen Fixation In nitrogen-fixing bacteria 1. Atmospheric N 2 is first reduced to NH 3 ; 2. In bacterial cells, NH 3 becomes NH 4 +, oxidized to NO 2 - and then to NO 3 - ; 3. NH 3, NH 4 +, and NO 3 - can be released into the surroundings (water or soils) and become available to plants; Denitrifying bacteria (in soils) change NO 3 - back to NO 2 -, NH 3, and finally to N 2 to complete the biological nitrogen cycle.

10 Biological Fixation and The Nitrogen Cycle

11 Industrial Nitrogen Fixation Industrial Fixation (the Haber Process): N 2 (g) + 3H 2 (g) 2NH 3 (g) Most NH 3 are converted to: 1. Fertilizers (~70%) 2. Nitric acid, HNO 3 (~20%) ΔH = -92 kj 3. Hydrazine, N 2 H 4, and monomers for various plastics and nylons.

12 The Haber Process

13 Important Hydrides of Nitrogen Ammonia, NH 3 (most important hydride) Production of fertilizers (NH 4 NO 3, (NH 4 ) 2 SO 4, (NH 4 ) 3 PO 4, and CO(NH 2 ) 2 ), HNO 3, and N 2 H 4 Hydrazine, N 2 H 4 Rocket propellant, manufacture of plastics, agricultural pesticides; Monomethylhydrazine, CH 3 N 2 H 3 Rocket fuels

14 Production of HNO 3 Oswald Process: 1. NH 3 (g) + O 2 (g) NO(g) + H 2 O(g) 2. 2NO(g) + O 2 (g) NO 2 (g) 3. 3NO 2 (g) + H 2 O(l) 2HNO 3 (aq) +NO(g) HNO 3 - a strong acid and an oxidizing agent; Reactions with metals does not produce H 2 Cu(s) + 4HNO 3 (16 M) Cu(NO 3 ) 2 (aq) + 2NO 2 (g) + 2H 2 O(l) 3Cu(s) + 8HNO 3 (aq, 6 M) 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) 4Zn(s) + 10HNO 3 (aq, 3 M) 4Zn(NO 3 ) 2 (aq) + N 2 O(g) + 2H 2 O(l)

15 Allotropes of Phosphorus White Phosphorus: P 4 (tetrahedral) - very reactive Black Phosphorus: crystalline structure - much less reactive Red Phosphorus: amorphous with P 4 chains

16 Allotropes of Phosphorus White very reactive Black Red P (white) (heat, 1 atm, no air) P (black) P (white) or P (red) (high pressure) P (black)

17 Oxides of Phosphorus Reaction of white phosphorus with oxygen: 1. P 4 (s) + 3O 2 (g) P 4 O 6 (l); (o.s. of P = +3) 2. P 4 (s) + 5O 2 (g) P 4 O 10 (s); (o.s. of P = +5) Reactions of phosphorus oxides with water: 1. P 4 O 6 (l) + 6H 2 O(l) 4H 3 PO 3 (aq); 2. P 4 O 10 (s) + 6H 2 O(l) 4H 3 PO 4 (aq); phosphorus in orange, oxygen in red

18 Oxyacids of Phosphorus Phosphoric acid, H 3 PO 4 - triprotic Phosphorous acid, H 3 PO 3 - diprotic Hypophosphorous acid, H 3 PO 2 - monoprotic

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20 ATP Adenosine triphosphate ADP Adenosine diphosphate

21 Phosphorus Halides Reactions of white phosphorus with halogens: 1. P 4 (s) + 6X 2 4PX 3 (l); 2. P 4 (s) + 10X 2 4PX 5 (s); Examples of reactions: PCl 3 (l) + Cl 2 (g) PCl 5 (s) PCl 3 (l) + 3H 2 O(l) H 3 PO 3 (aq) + 3HCl(aq) PCl 5 (s) + 4H 2 O(l) H 3 PO 4 (aq) + 5HCl(aq)

22 Important Compounds of Phosphorus Ca 3 (PO 4 ) 2 & Ca 5 (PO 4 ) 3 F : source of phosphorus Ca 5 (PO 4 ) 3 (OH) : forms bones and teeth P 4 O 10 : formation of H 3 PO 4 H 3 PO 4 : production of fertilizers & phosphates H 2 PO 4 - & HPO 4 2- : phosphate buffers Na 3 PO 4 : scouring powder and paint remover Na 5 P 3 O 10 : fabric softeners ADP & ATP : storage of metabolic energy PCl 5 : precursor for lithium hexafluorophosphate (LiPF 6 ), an electrolyte in lithium ion batteries;

23 Group 16, 6A Valence-shell configuration: ns 2 np 4 O, S, Se, Te, Po None of the Group 6A elements behaves as a typical metal. Elements form covalent bonds with other nonmetals.

24 Some Physical Properties

25 For S, Se, Te - similar gases with characteristic odor, poisonous

26 Hydrogenchalkogenides (HS) I and chalkogenides S II Soluble in water alikali metals, alkaline earth and NH 4 + Heavy metal sulfides non-soluble precipitation from aqueous solutions - Sulfur used for removing small amounts of elemental mercury - Melting of sulfides with sulfur polysulfides; e.g. Iron(II) disulfide FeS 2 (pyrite)

27 Oxygen O 2 makes up 21% of the Earth s atmosphere. O 3 (ozone) exists naturally in the upper atmosphere (the stratosphere) of the Earth. Ozone forming at electric discharges - pale blue gas Ozone layer absorbs UV light and acts as a screen to block most uvradiation from reaching the Earth s surface. We now know that Freons (CFCs = chloro-fluorocarbons) are promoting destruction of ozone layer.

28 Strong oxidizing agent

29 Various Forms of Oxides Metal oxides (ionic) 1. Nonconductor example: MgO 2. Semiconductor example: NiO 3. Conductor example: ReO 3 4. Superconductor example: YBa 2 Cu 3 O 7 Nonmetal oxides (covalent): Molecular oxides examples: CO 2, NO, NO 2, N 2 O, SO 2, P 4 O 10, etc. Covalent network oxide SiO 2

30 Characteristics of Oxides Metallic oxides basic or amphoteric Examples: Na 2 O (basic); Al 2 O 3 (amphoteric) Semi-metallic oxides mild to weakly acidic Example: B 2 O 3 Nonmetallic oxides weak to strong acids Examples: 1. SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) (weak acid); 2. SO 3 (g) + H 2 O(l) H 2 SO 4 (aq) (strong acid);

31 Redox properties of water Hydrogen peroxide in solid weak acid disproportionation ΔH o of 98.2 kj/mol; ΔS of 70.5 J/(mol K) Redox properties in acidic env. in basic env.

32 Sulfur is found in nature both in large deposits of the free element and in ores such as: Galena = PbS, Cinnabar = HgS, Pyrite = FeS 2, Sulfur Gypsum = CaSO 4 2H 2 O, Epsomite = MgSO 4.7H 2 O, and Glauberite = Na 2 Ca(SO 4 ) 2

33 Sulfur Mining: Frasch Process

34 Aggregates of Sulfur

35 Sulfur Oxides and Oxyacids S(s) + O 2 (g) SO 2 (g) 2SO 2 (g) + O 2 (g) 2SO 3 (g) SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) SO 3 (g) + H 2 O(l) H 2 SO 4 (aq) H 2 SO 3 diprotic; weak acid H 2 SO 4 diprotic; strong acid

36 Sulfuric Acid Productions: 1. S 8 (s) + 8 O 2 (g) 8SO 2 (g); 2. 2H 2 S(g) + 3 O 2 (g) 2SO 2 (g) + 2H 2 O(l); 3. FeS 2 (s) + 11 O 2 (g) Fe 2 O 3 (s) + 8SO 2 (g); 4. 2SO 2 (g) + O 2 (g) 2SO 3 (g); (V 2 O 5 /K 2 O catalyst) 5. 2SO 3 (g) + H 2 SO 4 (l) H 2 S 2 O 7 (l); 6. H 2 S 2 O 7 (l) + H 2 O(l) 2H 2 SO 4 (l);

37 Oxyacids of sulfur Sulfuric acid Sulfurous acid Polysulfuric acids H 2 SO 4.nSO 3 Peroxymonosulfuric acid di- Disulfurous acid Thiosulfurous acid Peroxydisulfuric acid Dithionous acid Dithionic acid Polythionic acids Thiosulfuric acid

38 Important Compounds of Sulfur H 2 SO 4 most important compound, for manufacture of fertilizer, soap, detergents, metal and textile processing, sugar refinery, and organic syntheses; SF 4 for fluoridation SF 6 as insulating and inert blanket Na 2 S 2 O 3 as reducing agent and complexing agent for Ag + in photography (called hypo ); P 4 S 3 in strike-anywhere match heads

39 Exercise #8 Draw Lewis structures for the following molecules: 1. SO 2 2. SF 2 3. SF 4 4. SF 6 5. H 2 SO 4 6. H 2 SO 3 7. H 2 S 2 O 7