Inorganic Solids

Inorganic Solids is a set of six lectures within CH1401. It covers an introduction to the composition both chemically and physically of simple inorganic solids.

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Content
The properties of a material are determined by its composition and structure. Materials can be classified either by structure or properties, depeding upon their position on the periodic table, purity, size, functions (eg charge, conductivity, appearence, catalysis) and structural properties (eg hardness, strength, flexibility).

Bonding
Metals are compounds whose electrical conductivity decrease where temperature increases (due to increased heat causing the overall lattice to move more, removing the electrons' previous easy motion even though they too are moving faster). They exist in a closely packed structure with delocalised electrons (obeying the band theory), and have both good thermal and electrical conduction. They also have a lustrous appearence and are strong whilst malleable.

Ionic solids are formed by electron exchange between a number of atoms. Their electrons cannot move, giving the materials insulating properties, and although their bond energies are high they are very brittle.

Covalent solids have localised electrons and distinct directional bonding (unlike ionic lattices, which exist in disorder) as well as insulating properties and weaker bond strengths.

Although these categories are useful, in reality most compounds are not entirely one or the other of these but somewhere between. In ambiguous cases it can be more useful to categorise compounds by their electronegativity (found by 1/2(Ionisation energy+electron affinity))and chemical hardness (1/2(EI-Ae)).

Hard and Soft Compounds
A species is chemically 'hard' if it is small with high charge and low ability to polarise. Likewise 'soft' species are large, with low charges and high ability to polarise. Hard reacts quickly and forms stronger bonds with hard, whereas soft reacts quickly and forms stronger bonds with soft. Much like polarity this embodies the like-to-like system found in chemistry.