Ionic vs. Covalent Bonds

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Krupa Prajapati
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Ionic vs. Covalent Bonds

Postby Krupa Prajapati » Wed Nov 01, 2017 10:12 am

Hi! I was just wondering how we can predict an ionic or covalent bond will form. Is it typically that a nonmetal and metal form an ionic bond, and two nonmetals form covalent bonds? Also with regards to polarity, how do we determine precisely if a molecule is polar or non polar. I remember in high school we had to check the electronegativities, but I am not so sure. If someone could help me clarify that would be great!

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Re: Ionic vs. Covalent Bonds

Postby Chem_Mod » Wed Nov 01, 2017 10:21 am

You are quite right in looking at the electronegativities of each atom. We can look at the difference between these electronegativities and have a good idea of what type of bond it is.

If the differences in electronegativities is less than 0.5 (eg. C and H), then this bond is non-polar covalent.
If the differences is between 0.5-1.5 (eg. C and O), then this bond is polar covalent.
If the differences is greater than 2.0 (eg. Na and Cl), then this bond is ionic.

These numbers aren't strict rules, but a general guide. Hope this helps!

Ethan Mondell 1A
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Re: Ionic vs. Covalent Bonds

Postby Ethan Mondell 1A » Wed Nov 01, 2017 8:49 pm

Just to add a little more, if the difference in electronegativities falls between the 1.5 and 2.0 difference gap, then you can always consider that some Ionic bonds have covalent characteristics. This means that even if there is an Ionic bond between two atoms, they can still be sharing the electrons between them to a certain extent. For example, AgBr has more covalent characteristics than AgF because the electronegative difference between Ag and Br isn't as great as that of Ag and F.

Emily Oren 3C
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Re: Ionic vs. Covalent Bonds

Postby Emily Oren 3C » Wed Nov 01, 2017 8:59 pm

Also, some molecules with polar covalent bonds are overall nonpolar due to their symmetry. For example, CO2 is a nonpolar molecule even though the C to O bond is polar covalent (electronegativities: 3.5-2.5=1 which is between .5 and 1.5). This is because it is symmetrical, so the partial negative charges on the oxygens "cancel".(CO2 molecule: O=C=O)

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