Carbon dioxide, CO2 and Silicon (IV) dioxide, SiO2 do not conduct electricity, simply because they do not have free electrons. For conducting electricity, free valence electrons are required. In case of metals, valence electrons are generally available and that is why they are (generally) good conductors of electricity. Non-metals, on the other hand, are generally bad conductors of electricity since they cannot provide free valence electrons. Apart from metals and non-metals, there are semiconductors like Silicon, where electrons can move from valence band to conduction band on application of electric field and thus be capable of electrical conductivity. Here, both the compounds, CO2 and SiO2, have stable electronic configurations due to bonding. For example, carbon is sharing the 4 valence electrons of 2 oxygen molecules, making both Carbon and Oxygen achieve fully filled orbitals. Thus, lack of free electrons make CO2 and SiO2 bad conductors of electricity.
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