Chemistry Revision Notes - Semiconductors, Superconductors & Oxidation States

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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) and the peroxides (the oxidation state for oxygen is -1).

In the compounds, halides usually have the oxidation number -1.

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The sum of all the oxidation numbers in a compound have to be equal to zero.

The sum of all the oxidation states in a complex ion is the same as the charge on the ion.


A covalent element such as silicon or germanium which has a higher conductivity than that of a typical non-metal but a much lower conductivity than that of a metal is described as a semiconductor.

Semiconductors are also referred to as metalloids and they occur at the division between metals and non-metals in the Periodic ...

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