1 / 42

Descriptive Chemistry

Descriptive Chemistry. Introduction to Descriptive Chemistry s-Block Elements p-Block Elements d-Block Elements f-Block Elements. Introduction to Descriptive Chemistry. Definition: “…the study of the composition, structure, and properties of matter….” - the facts about the

rosalba
Download Presentation

Descriptive Chemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Descriptive Chemistry • Introduction to Descriptive Chemistry • s-Block Elements • p-Block Elements • d-Block Elements • f-Block Elements

  2. Introduction to Descriptive Chemistry Definition: “…the study of the composition, structure, and properties of matter….” - thefacts about the elements and their compounds. Comments from the Experts: “…evident differences between this and previous editions…is the absence of much theoretical material previously included…the continuing rapid growth of chemistry…required the addition of impor- tant new factsto all of the descriptive material…over the years, become less persuaded of the value of certain types of theorizing….Thus, we felt obliged to make space forfacts at the expense of theoretical material.” Cotton and Wilkinson, Advanced Inorganic Chemistry, 5th Edition, 1988.

  3. Comments from the Experts: “The facts concerning the properties and reactions of substances are the very essence of chemistry. Facts undergo little if any change in contrast to constantly changing theories. Moreover, …a chemist needs a solid background of facts in order to appreciate the need for theories….” R. J. Gillespie in the Forward of Chemistry of the Elements, Greenwood and Earnshaw, 1st Edition, 1984.

  4. “Over the years, the theoretical part tended to grow at the expense of the descriptive material….The theoretical part tended to become the end rather than the means….By the 1970’s many teachers had to abandon any attempt to cover descriptive inorganic chemistry in the traditional sense. Thus we can encounter the student who can write an erudite account of structural minutiae in copper(II) chemistry, ligand field spectra and…,but who knows little about the more mundane compounds of the transition elements and would be hard pressed to locate indium in the Periodic Table, let alone venture anything about its chemistry.” Derek W. Smith, Inorganic Substances: A Prelude to the Study of Descriptive Inorganic Chemistry, 1st Edition, 1990.

  5. “Chemistry has always been, and still is, a practical subject….An American professor told me he divided inorganic chemistry books into two types: theoretical and practical. In deciding how to classify any particular book, he first looked to see if the extraction of the two most produced metals (Fe and Al) was adequately covered, what impurities were likely to be present, and how the processing was adapted to re- move them. Second, he looked to see if the treatment of the bonding in xenon compounds and ferrocene was longer than that of the pro- duction of ammonia. Third, he looked to see if the production and uses of phosphates were covered adequately….For some years there has been a trend for chemistry teaching to become more theoretical. There is always theoretical interest in another interesting oxidation state or another unusual complex, but the balance of this book is tilted to ensure that they do not exclude the commonplace, the mun- dane and the commercially important.”J. D. Lee, Concise Inorganic Chemistry, 5th Edition,1996.

  6. To theorize is human; to ‘describe’ is divine ! B. K. Christmas, 1992. • Descriptive Chemistry Outlined: • Family Characteristics/Trends • Occurrence, Preparation, and Production • Atomic, Molecular, and Physical Properties • Chemical Properties • Unique or Unusual Chemical Properties • Applications/Uses • Other Important Facts

  7. s-Block Elements H He Li Be Na Mg K Ca Rb Sr Cs Ba Fr Ra The s-Block elements consist of the elements hydrogen, helium, the alkali metals, Group 1, and the alkaline earth metals, Group 2.

  8. Hydrogen and the Hydrides Chapter 9 Occurrence and Abundance: Elemental Composition of the Sun and the Universe - Sun Universe Hydrogen92.5 % 90.87 % Helium 7.3 % 9.08 % All Others 0.2 % 0.05 % Elemental Composition of the Earth’s Crust (ppm by mass) - O - 455 000 Mg - 27 640 Si - 272 000 Na - 22 700 Al - 83 000 K - 18 400 Fe - 62 000 Ti - 6320 Ca - 46 600 H - 1520

  9. Hydrogen and the Hydrides Chapter 9 Elemental Composition of the Human Body: By Atoms By Mass H - 63.0 % 10.0 % O - 25.5 % 64.6 % C - 9.5 % 18.0 % N - 1.4 % 3.1 % Hydrogen also occurs in very large quantities in the ocean and is present in more compounds than any other element.

  10. Hydrogen and the Hydrides Chapter 9 Important History: 1671 - Robert Boyle - Noted a flammable gas formed when iron was reacted with sulfuric acid. 1766 - Henry Cavendish - Reacted acids with Fe, Zn, and Sn and, thus, established the true properties of the element. 1781 - Henry Cavendish - Showed quantitatively that water was formed when hydrogen was burned with oxygen, proving that water was NOT an element. 1783 - Antoine Lavoisier - Proposed the name “hydrogen” from the Greek for “water former”.

  11. Hydrogen and the HydridesChapter 9 Properties of Atomic Hydrogen: 1. Electron Configuration - 1s1 2. Atomic Radius - ~ 30 pm 3. First Ionization Energy - 1311 kJ/mol 4. Electron Affinity - +72 kJ/mol

  12. Hydrogen and the HydridesChapter 9 Ortho and Para Hydrogen: Ortho - Nuclear spins are parallel Para -Nuclear spins are anti-parallel These materials have different physical properties because of differences in internal energy. The para form is more stable and is the only form present at 0K.

  13. Hydrogen and the Hydrides Chapter 9 Electronic Structure and Modes of Reaction: Hydrogen has the simplest electronic structure of all elements. It consists of a nucleus containing one proton and one electron in the 1s orbital. 1s1 electron

  14. Hydrogen and the Hydrides Chapter 9 Modes of Reactivity: 1. By losing an electron to form a hydrogen ion, H+. + Protons are extremely small and, therefore, are VERY polarizing because they have a very large charge density. They associate strongly with molecules around them. Thus, in water or in acids they form the hydronium ion, H3O+.

  15. Hydrogen and the Hydrides Chapter 9 2. By gaining an electron to form a hydride ion, H -. - Hydride ions, H -, exist in the ionic crystalline solids of some of the Groups 1 and 2 metal hydrides. Only the most elec- tropositive metals will react to form ionic (saline) hydrides.

  16. Hydrogen and the Hydrides Chapter 9 • 3. By forming an electron pair (covalent) bond with • another atom. .. H •• Cl : .. .. H •• Cl : .. .. H : Cl : Non-metals and some metals form covalent hydrides. ..

  17. Hydrogen and the HydridesChapter 9 Molecular Properties of Hydrogen: Over 40 Forms of Hydrogen Exist - H, H2 H+, H-, H2+, H3+, D, D2, D+, D-, HD, HT, DT, T, T2, nuclear spin isomers, etc. Isotopes of Hydrogen - A. Protium - 1H 1 P+ B. Deuterium - 2H 1 P+ + 1 n0 C. Tritium - 3H 1 P+ + 2 n0 (99.986 %) (0.014 %) (7 x 10-16 %)

  18. Hydrogen and the HydridesChapter 9 Physical Properties: H2 D2 T2 Atomic Mass, u 1.0078 2.0141 3.0160 Freezing Point, oC -259.0 -254.3 -252.4 Boiling Point, oC -252.6 -249.3 -248.0 Bond Length, pm 74.14 74.14 (74.14) DHDissociation, kJ/mol 435.9 443.4 446.9 DHFusion, kJ/mol 0.117 0.197 0.250 DHVaporization, kJ/mol 0.904 1.226 1.393 Vapor Pressure, torr 54 5.8 -

  19. Hydrogen and the HydridesChapter 9 Physical Properties: H2O D2O Freezing Point, oC 0 3.82 Boiling Point, oC 100 101.42 Density at 20oC, g/mL 0.917 1.017 Ion Product (25oC) 1.0 x 10-14 3.0 x 10-15 Dielectric Constant (20oC) 8280.5 NaCl Solubility, g/100 g H2O 35.9 30.5 WHY??? The differences in properties noted in these tables are called, isotope effects.

  20. Hydrogen and the HydridesChapter 9 For Your Contemplation: Why should the melting point, boiling point, and DHVap be higher for D2 than for H2? Consider: Both are non-polar. Both are about the same size. Both have the same number of electrons.

  21. Hydrogen and the HydridesChapter 9 Chemical Properties: H2 D2 T2 They are essentially identical except for reaction rates and equilibrium constants. Preparation of Isotopes: • 1. D2O is prepared by the electrolysis of H2O. Since H2 • is liberated at a faster rate than D2, the water • becomes enriched in D2O. • 2. D2O can then be used in “exchange” reactions and • direct reactions to produce deuterated compounds.

  22. Hydrogen and the HydridesChapter 9 NaOH + D2O NaOD + HDO NH4Cl + D2O NH3DCl + HDO Mg3N2 + 3 D2O 2 ND3 + 3 MgO SO3 + D2O D2SO4 P4O10 + D2O D3PO4

  23. Hydrogen and the HydridesChapter 9 • 3. Tritium is prepared on a large scale by the following • reaction: 6Li + 1n 4He + 3T 3T has a t1/2 = 12.26 y and is a b-emitter. 3T ??? + b- What is the product of 3T decay?

  24. Hydrogen and the HydridesChapter 9 Synthesis and Production of Hydrogen: Commercial Production - • 1. “Water Gas” Reaction • C (s) + H2O (g) H2 (g) + CO (g) • This is an inexpensive process that produces “water • gas which is an important industrial fuel source. • H2 (g) + CO (g) + O2 (g) CO2 (g) + H2O (g) + thermal • energy

  25. Hydrogen and the HydridesChapter 9 H2 is difficult to purify from the water gas mixture. However, it can be done using the following reaction: H2O (g) 2 H2 (g) + CO2 (g) H2 (g) + CO (g) 450oC Fe2O3 H2 (g) + CO2 (g) + K2CO3 (aq) + H2O (l) 2 KHCO3 (aq) + H2 (g)

  26. Hydrogen and the HydridesChapter 9 • 2. Steam-Hydrocarbon Reforming • A. Natural gas or oil refinery feedstock desulfur- • ization • H2S (g) + 2 NaOH (aq) Na2S (aq) + H2O (l) • B. Reforming 760 - 980oC 600 psi Ni Cat. CH4 (g) + H2O (g) CO (g) + 3 H2 (g) Endothermic

  27. Hydrogen and the HydridesChapter 9 Two reversible reactions occur setting up an equilibrium mixture of H2, CO, CO2, and H2O: CO (g) + H2O (g) CO2 (g) + H2 (g) CO (g) + 3 H2 (g) CH4 (g) + H2O (g) C. High Temperature Shift Reaction 350oC Fe/Cu Cat. CO (g) + H2O (g) CO2 (g) + H2 (g) Exothermic

  28. Hydrogen and the HydridesChapter 9 D. Low Temperature Shift Reaction 200oC CO (g) + H2O (g) CO2 (g) + H2 (g) Exothermic This reduces CO content to about 0.2 % by volume. E. Methanation (For further removal of CO) 350oC CO (g) + H2 (g) CH4 (g) + H2O (g) • F. CO2 Removal • 2 HOCH2CH2NH2 + CO2 + H2O • (HOCH2CH2NH3 )2CO3

  29. Hydrogen and the HydridesChapter 9 K2CO3 (aq) + CO2 (g) + H2O (l) 2 KHCO3 (aq) • G. Pressure-Swing Absorption (PSA) • Low temperature shift and methanation can both be • replaced by this method which involves passing gas from • high temperature shift reactor through molecular sieves to • produce hydrogen with 99.9 % purity. The hydrocarbon-steam reforming process can also be done using the products of the “cracking” process in oil refineries, e.g., C3H8 (g) + H2O (g)

  30. Hydrogen and the HydridesChapter 9 3. Electrolysis of NaOH (aq) or KOH (aq) Anode: 2 OH- H2O + 1/2 O2 + 2 e- Cathode: 2 H2O + 2 e- 2 OH- + H2 2 H2O 2 H2 + O2 Ni anodes and Fe cathodes are used in this process. This process is the most expensive method for producing H2.

  31. Hydrogen and the HydridesChapter 9 • 4. Electrolysis of Brine - A By-product of the production • of chlorine in the chlor-alkali industry. 2 NaCl (aq) + 2 H2O (l) Cl2 (g) + H2 (g) + NaOH (aq) Laboratory Synthesis - Insufficient Hydrogen is found in the atmosphere. There- fore, it must be produced from compounds containing it. 1. Water as a Source for Hydrogen - A. At ordinary temperatures 1) By highly electropositive metals

  32. Hydrogen and the HydridesChapter 9 2 Na (s) + 2 H2O (l) NaOH (aq) + H2 (g) Ca (s) + 2 H2O (l) Ca(OH)2 (s) + H2 (g) 2) By hydrides of electropositive metals LiH (s) + H2O (l) LiOH (aq) + H2 (g) CaH2 (s) + 2 H2O (l) Ca(OH)2 (s) + 2 H2 (g) 3) By electrolysis of acidified solution 2 H2O (l) 2 H2 (g) + O2 (g)

  33. Hydrogen and the HydridesChapter 9 B. At higher temperatures Mg (s) + H2O (g) MgO (s) + H2 (g) Zn (s) + H2O (g) ZnO (s) + H2 (g) 3 Fe (s) + 4 H2O (g) Fe3O4 (s) + H2 (g) All of these are Exothermic CO (g) + H2O (g) CO2 (g) + H2 (g) C (s) + H2O (g) H2 (g) + CO (g)

  34. Hydrogen and the HydridesChapter 9 2. Non-Oxidizing Acids as a Source for Hydrogen - Zn (s) + dil. H2SO4 (aq) ZnSO4 (aq) + H2 (g) Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g) Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g) Oxidizing acids DON’T WORK!! Zn (s) + HNO3 (aq) Zn(NO3)2 (aq) + NH4NO3 + H2O (l) Assignment: Balance this equation!

  35. Hydrogen and the HydridesChapter 9 3. Bases as a Source for Hydrogen - Zn (s) + 2 NaOH (aq) + 2 H2O (l) Na2[Zn(OH)4] + H2 (g) Al (s) + 2 KOH (aq) + 2 H2O (l) K2[Al(OH)4] + H2 (g)

  36. Hydrogen and the HydridesChapter 9 Chemical Properties of Molecular Hydrogen: DHdissociation = 436 kJ/mol Types of Reactions - HX H2O -C-C- O2 X2 C=C N2 M MHx H2 NH3 MxOy C=C C=O -C-C- M + H2O -C-OH

  37. Hydrogen and the HydridesChapter 9 Saline (“Salt-Like”) Hydrides:

  38. Hydrogen and the HydridesChapter 9 Saline hydrides are binary compounds containing dis- crete hydride ions, H-. Very electropositive metals are needed to form these. WHY? H -67.8 kJ Cl H- 218 kJ 119 kJ -364 kJ 1/2H2 1/2Cl2 218 kJ - 67.8 kJ = + 150 kJ = DHform Cl- 119 kJ - 364 kJ = - 245 kJ = DHform

  39. Hydrogen and the HydridesChapter 9 Only the most electropositive metals have low enough ionization potentials to form ionic hydrides. Na, K, Rb, Cs, Ca, Sr, Ba LiH and MgH have some ionic character. • 1. Preparation of Saline Hydrides • 300 - 700oC • 2 M + H2 2 MH • M + H2 MH2 Li > Cs > Rb > K > Na Rate of Reaction

  40. Hydrogen and the HydridesChapter 9 2. Properties of Saline Hydrides Their ionic character is demonstrated by the conduc- tivity of the molten hydride and the liberation of H2 at the anode during electrolysis of the molten hydride. The white crstalline solids are soluble in molten alkali halides: LiCl/KCl - 360oC Electrolysis CaH2H2at the anode.

  41. Hydrogen and the HydridesChapter 9 MH + H+ M+ + H2 (g) LiH (s) + H2O (l) LiOH (aq) + H2 (g) Saline hydrides are very strong reducing agents. 4 LiH + AlCl3 LiAlH4 + 3 LiCl Only LiH can be melted without thermal decomposition. 2 MH 2 M + H2 (g) D

  42. Hydrogen and the HydridesChapter 9 Commercial Applications of Molecular Hydrogen: The Haber Process - 3 H2 (g) + N2 (g) 2 NH3 (g) Molecular hydrogen as a reducing agent - FeO + H2 Fe + H2O 2 Fe2O3 + H2 4 Fe + 6 H2O CuO + H2 Hg + H2O

More Related