Variability and relative stability of oxidation states

Matt Carruthers Variability and relative stability of oxidation states In this essay the concentration will be on the oxidation states of the transition metals rather than the entire periodic table. An oxidation state is a number assigned to an element in a compound according to some rules. This number enables us to describe oxidation-reduction reactions, and balancing redox chemical reactions. Compared to Group II elements such as calcium, transition elements form ions with a wide variety of oxidation states. Calcium ions typically don't lose more than two electrons, whereas transition metals can lose up to nine. The energies required to remove electrons from calcium are low until you try to remove electrons from below its outer two s orbitals. In fact Ca3+ has an ionisation enthalpy so high that it rarely occurs naturally. However a transition element like vanadium has roughly linear increasing ionisation enthalpies throughout its s and d orbitals, due to the close energy difference between the 3d and 4s orbitals. Transition metal ions are therefore commonly found in very high states. Certain patterns can be seen to emerge across the period of transition elements: The number of oxidation states of each ion increases up to Mn, after which they start to drop. This drop is due to the stronger pull from the protons in the nucleus towards the electrons, making them

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Method's of Drug Characterisation

Experiment 6 - Methods of Drug Characterization Aims . To gain experience of the analytical methods used for drug characterization Objectives . To gain experience in melting point determination, thin layer chromatography and UV spectroscopy 2. Application of the methods to identify an unknown substance Introduction The 2 most basic analytical techniques for identification of organic compounds are melting point determination and thin layer chromatography. Identification of compounds relied upon melting point determination before the modern analytical techniques of nuclear magnetic resonance, infrared and UV spectroscopy. Although thin layer chromatography still plays an important role in organic analysis. A solution of the unknown is spotted onto the silica coated plate about 1cm from the bottom and dried; it is then placed vertically into a tank with a suitable solvent inside. The solvent moves up the plate by capillary action and resolves the sample into discrete spots. The plate is removed and dried and the spots are viewed under UV or by treating it chemically with developing agent. For each component of the sample an Rf value can be calculated: Rf = distance moved by solute/distance moved by solvent Safety * Local rules apply * The sealing of melting point tubes by Bunsen must be done away from flammable solvents * After practical all waste solvents

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"Environmental degradation is neither the inevitable price of, nor a desirable path for, economic development

"Environmental degradation is neither the inevitable price of, nor a desirable path for, economic development." (UNDP, et al, 2005) Introduction Environmental degradation is now apparent on a global scale. In addition to the deterioration of what were once considered free goods (such as air and water), escalating scarcity of natural resources, deforestation, desertification and threatened bio-diversity are now commonplace across the spectrum. There are certainly no reservations over the scale of this degradation, however there is much controversy concerning the apparent environmental degradation - economic development nexus. Many have argued that short-term tradeoffs exist in the form of environmental degradation, for superior long-term economic gains. One of the positions put forward is that environmental degradation is the result and inevitable price of economic development. This viewpoint is based on the Environmental Kuznets Curve, regarding environmental degradation as the 'necessary evil' for achieving 'economic development' and suggesting that environmental assets are degraded in the early stages of economic development, only to improve after some income threshold has been passed at a later point. In the last decade, extensive literature has argued that a direct link between environmental degradation and economic development is too simplistic and that the

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