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Carbon vs Silicon and Carbon vs Silicon Dioxide

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    • Thread Starter

    Which substances from these pairs have the highest melting point? Why?

    The 'why' has me stumped, in all honesty.

    The carbon compounds. It's all to do with bond lengths. As you know, sigma bonds are just the attraction between the two nuclei and the two electrons localised in the bonding orbital. The attractions are electrostatic and the nuclei and electrons can be modeled as point charges, as in this rather classical diagram https://upload.wikimedia.org/wikiped...drogen.svg.png. Coulombs law states that the force is inversely proportional to the distance between the charges so naturally as the atomic radii get larger the distances between the bonding electrons and nuclei get larger and the force becomes weaker.

    Even in hydrogen it's a bit more complex than that, as you have to consider the repulsion between the nuclei as well as the attraction between the electrons and each nucleus. The effects of things like that are quite small though so unless you're calculating the actual bond length you tend to ignore them.
    • Thread Starter

    (Original post by Peroxidation)

    Thanks. That'll take me a while to get my head round, tbh.
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