3 Key excerpts on "Classification and Nomenclature"

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  eBook - ePub

  Philosophy of Chemistry

  • Dov M. Gabbay, Paul Thagard, John Woods(Authors)
  • 2011(Publication Date)
  • North Holland

    (Publisher)

  There is a further distinction between chemical equations and laws of physics, to do with the meaning of the notations. In physics, for the most part, ‘+’ and ‘=’ are to be read numerically. In chemistry the very same sign forms mean something quite different. ‘+’ means something like ‘reacting’, while ‘=’ means ‘gives rise to’ or something like that. Of course, as Benjamin Brodie pointed out, every chemical equation is accompanied by a ghostly sibling, in which the atomic weights of the elements are inserted. Then the meanings of the notation change radically. Juxtaposing letters in a chemical formula means ‘combined with’. Juxtaposing letters in the gravimetric equation means ‘add’.

  4. Chemical Taxonomies

  By mid-eighteenth century a firm distinction between elements and compounds had grown up. There were disagreements about the scope of these broad generic categories. Were ‘light’ and ‘heat’ chemical elements like ‘hydrogen’ and ‘sulphur’? However, the distinction was not called into question. Much as Linnaeus built the dual taxonomies of animals and plants, so nineteenth century chemists were much occupied with classification systems for elements and for compounds. The former led to the periodic table while the latter led to the nomenclature we still use for describing compounds in terms of their constituent elements (or radicals) and the proportions with which they are combined in the compound in question.

  Do we find another kind of law-like statement in the discourses with which the periodic table is described and its arrangements explained? The role of nominal and real essences, and so of theory in the analysis of the principles of such classifications have been much discussed in recent literature [Harré, 2005 , 7-30]. For the moment let us shelve the question of how real and nominal essence definitions are related. At this point it will be helpful to introduce a working distinction between the chemical properties of a substance and its physical properties. Chemical properties are those germane to procedures of substance transformation, except those brought about by radioactivity, natural or induced. Physical properties include observable attributes germane to producing changes of state, and importantly for the context of this chapter, those which are used in the setting up of the explanatory regresses which underpin our knowledge of chemical transformations.

  The Wikipedia (such a useful source!) offers the following account of Manganese. It is a ‘gray-white metal, resembling iron. It is a hard metal and very brittle, fusible with difficulty’. So far this is a list of physical properties, germane to such changes of state as liquifaction. Wikipedia then goes to add that it is easily oxidised, and ‘sulfur-fixing, deoxidizing, and alloying’. These are chemical properties, according to the above distinction, that is germane to the transformation of substances, for example iron into steel. Potassium permanganate (Condy's crystals) was well known in my childhood for its anti-bacterial properties.

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  eBook - ePub

  Science Knowledge for Primary Teachers

  Understanding the Science in the QCA Scheme

  • Linda Gillard(Author)
  • 2013(Publication Date)
  • David Fulton Publishers

    (Publisher)

  chemicals and is the basis for the study of chemistry, in the same way as living things are the basis for the study of biology. Living things are also made up of chemicals and so the two areas of study overlap in an area called biochemistry. All chemicals originally come from the reactions that take place in stars; so the Earth has been formed from stardust and so have we. So what is this stuff and how can we begin to explore it?

  We study the material world by grouping and classifying the materials we find. There are different ways of grouping stuff depending on our needs and the purpose of the study. This can be confusing sometimes if you attempt to match the language used in one classification system to the range of terms used when materials are grouped differently. Examples of such groups that will be considered in this chapter are: the periodic table, which organises the information about all the known basic chemicals; grouping common materials such as plastics and metals; and grouping by state into solids, liquids and gases. In order to understand the basis of these groupings, we need to understand what we mean by chemical properties, and it is interesting to relate this to chemical structure and an understanding of atoms and how they join together in different ways.

  Although initially we explore the world around us using our senses, chemists also rely on a range of apparatus that can sort and classify matter more quickly and using properties that we can only measure and not sense. For example, mass spectrometers detect very small mass differences and so identify different substances, X-rays have been used in X-ray crystallography, which was important in elucidating the structure of DNA, and Geiger counters enable us to detect radioactive chemicals. Children will initially explore the material world using their senses, tasting and smelling and feeling objects as well as looking and listening to them. We need to encourage this exploration but make them aware of safety issues. Adults need to control the environment of small children so that they do not lick harmful substances. Babies naturally explore everything they come into contact with using hands, mouth and feet, but as children become more independent, they need to learn that some substances are harmful and should be explored with more caution. However, with care, supervision, guidance and health and safety training, children can and should use all of their senses to explore all the different materials that make up our world. Smells, texture, temperature changes, sparks, colour and colour changes are the exciting bits of chemistry we all remember. It is a fascinating world and once we begin to understand some basic chemistry, we may never look at ‘stuff’ in quite the same way again.

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  eBook - ePub

  Flexible Polyurethane Foams

  A Practical Guide

  • Chris Defonseka(Author)
  • 2019(Publication Date)
  • De Gruyter

    (Publisher)

  The names of organic compounds can be systematic (following logically from a set of rules) or non-systematic (following various traditions). Systematic nomenclature starts with the name of the parent structure within the molecule of interest. This parent name is then modified by prefixes, suffixes and numbers to convey the structure unambiguously. Given that millions of organic compounds are known, rigorous use of systematic names can be cumbersome. Thus, these rules are followed closely for simple compounds but not for complex molecules. To use the systematic naming procedure, one must know the structure and names of the parent structure. Parent structures include unsubstituted hydrocarbons, heterocycles and monofunctionalised derivatives thereof.

  Non-systematic nomenclature is simpler and unambiguous (at least to chemists). Non-systematic names do not indicate the structure of a compound. Non-systematic names are common for complex molecules (which includes most natural products). Computer technology has enabled other naming methods to evolve that are intended to be interpreted by machines.

  2.2.8  Structural presentation

  Organic molecules can be described by drawings, structural formulae, combinations of drawings and chemical symbols. The line-angle formula is simple and unambiguous. In this system, the endpoints and intersections of each line represent one carbon atom, and hydrogen atoms can be notated explicitly or assumed to be present as implied by a tetravalent carbon. The depiction of organic compounds with drawings is greatly simplified by the fact that carbon in almost all organic compounds has four bonds, oxygen has two bonds, hydrogen has one bond and nitrogen has three bonds.

  2.3  Classification of organic compounds

  2.3.1  Functional groups

  The concept of functional groups is central to organic chemistry as a means to classify structures and for predicting properties. A functional group is a molecular model and the reactivity of that functional group is assumed (within limitations) to be the same in various molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified on the basis of their functional groups.

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