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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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Friday, December 23, 2011

The Difference in Electronegativity: Ionic VS Covalent Bond

Nothing is perfect. We have to remember this: Don't ever think that Sodium Chloride has only ionic bond and don't ever think that Hydrochloric Acid has only covalent bond. The truth is: Sodium Chloride may consist of 95% of ionic bond and 5% of covalent bond. Because the ionic bond is the dominant bond, covalent bond in Sodium Chloride is neglected. From the description above, we now know why Beryllium Chloride is amphoteric, why Titanium(IV) Chloride is a covalent compound, and why Permangate ion is a covalent ion, not an ionic ion. See the picture below:

(Source: http://www.green-planet-solar-energy.com/images/PT-small-electroneg.gif)

Electronegativity is the tend of an atom to attract electrons in its bond with another atoms. This is the primary key to know the characteristics and properties of a compound. Now let me give you some questions:

1. Why Ethanol has a higher boiling point than dimethyl ether?
2. Why barium sulfate insoluble in water otherwise magnesium sulfate is soluble in water?
3. Why water has the higher boiling point than hydrogen sulfide?
4. Why hydrofluoric acid is a weak acid?
5. Why hydrochloric acid is a polar compound?

You can answer all the question above with one answer: Because of the electronegativity. But you still have to explain it completely. There are some clues to identify the ionic characteristic of binary compound (Ex: NaCl):

The Difference of Electronegativity Range:
4 - 1.7 = Ionic
0.3 - 1.7 = Polar Covalent
0 - 0.3 = Non Polar Covalent.

For example, the EN of Na is 0.9 and Cl is 3.0 so the difference of EN is 2.1. It means sodium chloride is an ionic compound.

Further Reading . . .
Effendy. Ikatan Ionik dan Cacat - Cacat pada Kristal Ionik. 2nd Edition.

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