AL chem bonding

1. 點解cation charge density high 就會有strong polarizing power?

Polarizing power of a cation is the ability of the cation to draw back (polarize) the valence electron clouds of the anion.

For a cation carrying a higher positive charge, the attraction between the cation and the valence electron clouds of the anion would be stronger, and thus the cation draws back the valence electron clouds of the anion more readily.

For a cation have a smaller volume, the distance between the cation and the valence electron clouds of the anion would be shorter, and this leads to a strong attraction between them. Therefore, a smaller cation draws back the valence electron clouds of the anion more readily.

Consider the above two factors simultaneously. A strong polarizing power of a cation associates with a higher positive charge and a smaller volume of the cation. The charge density of a cation is defined as charge/volume. A higher positive charge and a smaller volume of a cation lead to a higher charge density. Hence, it can be deduced that a cation has strong polarizing power if it has higher charge density.


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2. CH4同埋CO2 都係overall non polar, CH 同 CO 係polar bond 點解dry ice ge CO2 molecule係dipole dipole 但CH4係induced dipole-induced dipole?

You have got incorrect idea.

Only polar molecules have dipole-dipole attractions. Since both CH4 and CO2 are non-polar, both of them have instantaneous dipole-induced dipole attractions.