Showing posts with label Chemistry. Show all posts
Showing posts with label Chemistry. Show all posts

Saturday, February 23, 2013

Har Gobind Khorana

Har Gobind Khorana, was born in 1922. He obtained his M.Sc. degree from Punjab University in Lahore. He worked with Professor Vladimir Prelog, who moulded Khorana’s thought and philosophy towards science, work and effort. After a brief stay in India in 1949, Khorana went back to England and worked with Professor G.W. Kenner and Professor A.R.Todd. It was at Cambridge, U.K. that he got interested in both proteins and nucleic acids. Dr Khorana shared the Nobel Prize for Medicine and Physiology in 1968 with Marshall Nirenberg and Robert Holley for cracking the genetic code.

Victor Grignard

Victor Grignard had a strange start in academic life for a chemist - he took a maths degree. When he eventually switched to chemistry, it was not to the mathematical province of physical chemistry but to organic chemistry. While attempting to find an efficient catalyst for the process of methylation, he noted that Zn in diethyl ether had been used for this purpose and wondered whether the Mg/ether combination might be successful. Grignard reagents were first reported in 1900 and Grignard used this work for his doctoral thesis in 1901. In 1910, Grignard obtained a professorship at the University of Nancy and in 1912, he was awarded the Nobel prize for Chemistry which he shared with Paul Sabatier who had made advances in nickel catalysed hydrogenation.

Alfred Werner (1866-1919)

Werner was born on December 12, 1866, in Mülhouse, a small community in the French province of Alsace. His study of chemistry began in Karlsruhe (Germany) and continued in Zurich (Switzerland), where in his doctoral thesis in 1890, he explained the difference in properties of certain nitrogen containing organic substances on the basis of isomerism. He extended vant Hoff’s theory of tetrahedral carbon atom and modified it for nitrogen. Werner showed optical and electrical differences between complex compounds based on physical measurements. In fact, Werner was the first to discover optical activity in certain coordination compounds.
He, at the age of 29 years became a full professor at Technische Hochschule in Zurich in 1895. Alfred Werner was a chemist and educationist. His accomplishments included the development of the theory of coordination compounds. This theory, in which Werner proposed revolutionary ideas about how atoms and molecules are linked together, was formulated in a span of only three years, from 1890 to 1893. The remainder of his career was spent gathering the experimental support required to validate his new ideas. Werner became the first Swiss chemist to win the Nobel Prize in 1913 for his work on the linkage of atoms and the coordination theory.

Principal Ores of Some Important Metals

Aluminium - Bauxite,  Kaolinite (a form of clay)

Iron  -   Haematite,  Magnetite,  Siderite,  Iron pyrites

Copper - Copper pyrites,  Malachite,  Cuprite,  Copper glanc

Zinc - Zinc blende or Sphalerite ZnS, Calamine,  Zincite ZnO

The Solid State

Solids have definite mass, volume and shape. This is due to the fixed position of their constituent particles, short distances and strong interactions between them. In amorphous solids, the arrangement of constituent particles has only short range order and consequently they behave like super cooled liquids, do not have sharp melting points and are isotropic in nature. In crystalline solids there is long range order in the arrangement of their constituent particles. They have sharp melting points, are anisotropic in nature and their particles have characteristic shapes. Properties of crystalline solids depend upon the nature of interactions between their constituent particles. On this basis, they can be divided into four categories, namely: molecular, ionic, metallic and covalent solids. They differ widely in their properties.
The constituent particles in crystalline solids are arranged in a regular pattern which extends throughout the crystal. This arrangement is often depicted in the form of a three dimensional array of points which is called crystal lattice. Each lattice point gives the location of one particle in space. In all, fourteen different types of lattices are possible which are called Bravais lattices. Each lattice can be generated by repeating its small characteristic portion called unit cell. A unit cell is characterised by its edge lengths and three angles between these edges. Unit cells can be either primitive which have particles only at their corner positions or centred. The centred unit cells have additional particles at their body centre (bodycentred), at the centre of each face (face-centred) or at the centre of two opposite faces (end-centred). There are seven types of primitive unit cells. Taking centred unit cells also into account, there are fourteen types of unit cells in all, which result in fourteen Bravais lattices.
Close-packing of particles result in two highly efficient lattices, hexagonal close-packed (hcp) and cubic close-packed (ccp). The latter is also called facecentred cubic (fcc) lattice. In both of these packings 74% space is filled. The remaining space is present in the form of two types of voids-octahedral voids and tetrahedral voids. Other types of packing are not close-packings and have less efficient packing of particles. While in body-centred cubic lattice (bcc) 68% space is filled, in simple cubic lattice only 52.4 % space is filled.

Solids are not perfect in structure. There are different types of imperfections or defects in them. Point defects and line defects are common types of defects. Point defects are of three types - stoichiometric defects, impurity defects and non-stoichiometric defects. Vacancy defects and interstitial defects are the two basic types of stoichiometric point defects. In ionic solids, these defects are present as Frenkel and Schottky defects. Impurity defects are caused by the presence of an impurity in the crystal. In ionic solids, when the ionic impurity has a different valence than the main compound, some vacancies are created. Nonstoichiometric defects are of metal excess type and metal deficient type. Sometimes
calculated amounts of impurities are introduced by doping in semiconductors that change their electrical properties. Such materials are widely used in electronics industry. Solids show many types of magnetic properties like paramagnetism, diamagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. These properties are used in audio, video and other recording devices. All these properties can be correlated with their electronic configurations or structures.

Elements, their Atomic Number

Element/Symbol/Atomic Number      

Actinium   Ac    89 

Aluminium  Al    13 

Americium  Am    95 

Antimony    Sb    51  

Argon     Ar    18  

Arsenic     As    33 

Astatine     At    85

Barium     Ba    56   

Berkelium     Bk    97 

Beryllium     Be     4 

Bismuth  Bi  83 

Bohrium  Bh  107 


Bromine  Br  35 

Cadmium  Cd  48   

Caesium  Cs  55 

Calcium  Ca  20 

Californium Cf  98   


Cerium  Ce  58 

Chlorine  Cl  17 

Chromium Cr  24 

Cobalt  Co  27 

Copper  Cu  29 

Curium  Cm  96 

Dubnium  Db  105 

Dysprosium Dy  66 

Einsteinium Es  99 

Erbium  Er  68 

Europium  Eu  63 

Fermium  Fm  100 

Fluorine  9

Francium  Fr  87 

Gadolinium Gd  64 

Gallium  Ga  31 

Germanium Ge  32 

Gold     Au  79 

Hafnium  Hf  72 

Hassium  Hs  108 

Helium  He 

Holmium  Ho  67 


Indium  In  49

Iodine  53

Iridium  Ir  77 

Iron         Fe  26 

Krypton  Kr  36 

Lanthanum La  57   

Lawrencium Lr  103 

Lead      Pb  82 

Lithium  Li 

Lutetium  Lu  71 

Magnesium Mg  12   

Manganese Mn  25 

Meitneium  Mt  109 

Mendelevium Md 101 

Mercury Hg  80    

Molybdenum Mo 42   

Neodymium Nd  60   

Neon  Ne  10   

Neptunium Np  93    

Nickel  Ni  28     

Niobium  Nb  41    


Nobelium  No  102   

Osmium  Os  76   


Palladium  Pd  46   

Phosphorus P  15     

Platinum  Pt  78   

Plutonium  Pu  94     

Polonium  Po  84  

Potassium  19   

Praseodymium  Pr  59   

Promethium  Pm  61   

Protactinium  Pa  91   

Radium  Ra  88   

Radon  Rn  86   

Rhenium  Re  75   

Rhodium  Rh  45   

Rubidium  Rb  37   

Ruthenium  Ru  44   

Rutherfordium  Rf  104   

Samarium  Sm  62   

Scandium  Sc  21   

Seaborgium Sg  106   

Selenium  Se  34   

Silicon  Si  14   

Silver  Ag  47     

Sodium  Na  11   

Strontium  Sr  38   

Sulphur  16   

Tantalum  Ta  73     

Technetium Tc  43   

Tellurium  Te  52   

Terbium  Tb  65   

Thallium  Tl  81   

Thorium  Th  90   

Thulium  Tm  69   

Tin      Sn  50   

Titanium  Ti  22   

Tungsten  74     

Ununbium  Uub  112   

Ununnilium Uun  110     

Unununium Uuu  111   

Uranium  92     

Vanadium  23   

Xenon  Xe  54     

Ytterbium  Yb  70   

Yttrium  39   

Zinc      Zn  30   

Zirconium  Zr  40