• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Chemistry Revision Notes - Semiconductors, Superconductors & Oxidation States

Extracts from this document...


´╗┐Oxidation States. The oxidation state or oxidation number, is a value assigned to a chemical species which represents its actual or nominal electrical charge. The oxidation number in a free or uncombined element is zero. This means that, metallic magnesium has an oxidation number of zero, and chlorine in Cl2 form has an oxidation state of zero. For simple ionic compounds, the oxidation state of the single atom ions is simply the charge on the ions. In most compounds the oxidation number for hydrogen is +1 and for oxygen is -2. The exceptions include the hydrides (the oxidation state is -1) ...read more.


Semiconductors are also referred to as metalloids and they occur at the division between metals and non-metals in the Periodic Table. Key facts : 1. The electrical conductivity of semiconductors increases with increasing temperature. 2: Doping pure crystals of silicon or germanium with certain other elements produces 2 types of semiconductors: n- type and p-type semiconductors. The addition of small quantities of certain substances to pure silicon greatly enhance its conductivity and makes possible the construction of electronic devices. This controlled addition of impurities is called ?doping?. 1. doping pure silicon with phosphorus or arsenic (group 5 elements) these elements have 5 valence electrons, a few of the silicon atoms are replaced by P, As atoms --- 1 electron is left over after the 4 bonds have been formed. ...read more.


We can think of this as a vacancy or hole in the bonding orbital. An electron from a neighbouring atom can move in to occupy this vacancy. As a result of this movement this type of conductor is called p-type. Superconductors 1. Superconductors are a special class of materials that have zero electrical resistance at temperatures near absolute zero. 2. Achieving temperatures near absolute zero is difficult and costly so application of superconduction at these temperatures is impractical. 3. Recently superconductors have been discovered which have zero resistance up to temperatures above the boiling point of liquid nitrogen- temperatures which are less costly to attain. 4. Superconductors may have a future applications in power transmission and electrically powered forms of transport. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Physical Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Physical Chemistry essays

  1. Alkaloids are the most diverse group of secondary metabolites and over 5000 compounds are ...

    Structure elucidation Classical era: The classical era for structural studies on alkaloids was the 19th Century, though this could be extended to the 1930's (advent of x-ray crystallography) or even to the 1970's (advent of high resolution NMR facilities and modern methods of mass spectroscopy.

  2. Describe the construction, operation and application of distillation equipment used in industry

    A good pressure drop compared to the price. Valve Trays: Nearly as much of a pressure drop as bubble caps, but other advantages make it a more profitable investment. Shower Trays: Very little pressure drop compared to other trays, even with the closest packing possible.

  1. Outline and examine some uses of different metals through history, including contemporary uses, as ...

    The first ionization energy increases across a period as electron shells go from near empty to full. The ionization energy decreases down a group as the outer electrons become further remove from the positive nucleus. The second ionization energy is always greater than the first since the electron is now being removed from a positive ion.

  2. Titration - Preparation,Neutralisation and Applications in Industry

    Redox titrations come in use in industry when extracting metals from their ore. There are many industries that require the use of titrations on a daily basis. For example Wineries, Pharmacies, Food & Drink makers, Cosmetics and Mining these are only a few from a massive list.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work