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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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The Documents

Friday, December 16, 2011

Grinberg's Polarization Theory and Its Relation with Solubility

First thing first, we agree that there is a periodic character of sulfate and hydroxide salt of alkali earth solubility in water (At 25 OC ). Down the group, the solubility of sulfate salt will be decreased. Otherwise, the solubility of hydroxide of alkali earth will be increased down the group.

My question is: What reason that makes those things happened?

Let me give an example:

We know that the solubility of Calcium Sulfate is so small (0.255 gram / 100 mL water at RTP) so that it will be found as a precipitate. The question still didn't answered, why Calcium Sulfate has that solubility?

In Grinberg's Polarization Theory, Grinberg suggested that the ligand T induces an additional, uncompensated dipole on the metal ion which opposes the natural dipole of the ligans "trans" to it and weakens the M-L bond in the ground state.



But what is the relation between this theory and the solubility above?

See the picture below:

We know that in ionic bond, there is a electrostatic force that attract Calcium ions and sulfate ions. When diluted, these ions will be solvated by water molecule so that they can't attract each other to make a precipitation (solid state). Well, I have to make you remember that there's nothing perfect but God. This compound not only has ionic bond but also covalent bond. The ionic character of this compound is stronger than its covalent bond so that we say this compound as a ionic compound.

The distribution of electrons in each ions can make a polarization between them so that the charge between those ions will be disappeared soon, make there is no charge between those ions and make them become a covalent compound that doesn't dissolved in water. This can be the reason why Calcium Sulfate found as precipitated in water at RTP.

And the last thing you have to memorize that the primary key to understand the bonds of compounds is: Electronegativity.

Further Reading:
Wikipedia
G. S. Manku. Theoretical Principles of Inorganic Chemistry. p521.

Source:
Documents of Pelatnas I IChO 2012


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