(Polar molecules, Non-polar molecules, etc.)

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Bao Tram Nguyen
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Joined: Sat Aug 24, 2019 12:17 am


Postby Bao Tram Nguyen » Thu Nov 14, 2019 7:19 pm

So for some homework problems, they only give you the name of the molecules and not the actual formula. Would this be the case on exams as well because I am stuck having to look up these molecules to find the formulas? Would you recommend me memorizing the prefixes that determine the number of atoms and if you can please give me some sort of key?

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Re: Prefixes

Postby nicolely2F » Thu Nov 14, 2019 10:36 pm

So far the exams have given us the formula, but it's very handy and potentially important to know the prefixes. I don't know any tricks so maybe memorization is the way to go. General rule for molecules is (numerical prefix + name of first atom, numerical prefix + name of second atom with "-ide" ending; if there's only one atom of the first element, you don't need the prefix mono)
Mono - 1 (Carbon monoxide)
Di - 2 (Carbon dioxide)
Tri - 3 (Sulfur trioxide)
Tetra - 4 (Tetraphosphorus)
Penta - 5 (Phosphorus pentachloride)
Hexa - 6 (Sulfur hexafluoride)
Hepta - 7 (Dichlorine heptaoxide)
Octa - 8 (Octasulfur)

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Re: Prefixes

Postby KDang_1D » Fri Nov 15, 2019 3:41 pm

In today's Friday lecture, we also learned the organic chemistry prefixes cis- and trans-. I don't think we should need to know how to draw organic molecules, but I think we should be familiar with general polarity. "Cis-" means same and "trans-" means opposite, so in general, when the two electronegative atoms are on opposite sides of the molecule their dipole vectors will cancel, making it nonpolar. Conversely, when the two electronegative atoms are together on the same side, the molecule will be polar.

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