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Final Exam Review

#7
by

Cyrus Ghaznavi

on 19 May 2011

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Transcript of Final Exam Review

#7 A Solid potassium conducts an electrical current, whereas solid postassium nitrate does not. The answer to this question is simple. First, we need to understand that in order to conduct an electrical current, electrons must be able to move freely. If we remember the way electrons gather in a metal (like K), we can see why electricity could be conducted: because the "sea of electrons" allows for a lot of room to move freely. An ionic compound like potassium nitrate does not have this advantage because its composition is in a rigid, crystal structure; therefore, electrons cannot move freely and thus electricity cannot be conducted (when melted, however, electricity can be conducted). B C D E F Antimony trichloride has measureable dipole movement, wheres antimony pentachloride does not. SF2, SF4, and SF6 are known to exist. However, OF2 is the only fluoride to exist with oxygen. Carbon tetrachloride has a lower boiling point than carbon tetrabromide. Sodium iodide is very soluble in water while iodine (I2) is not. The N-O bonds in NO2^-1 are equal in length, but they are unequal in HNO2. The issue here is simple: in order to have dipole movement, molecules need to be polar. As you can see by the sketches made according to VSEPR Theory, antimony trichloride is polar, while antimony pentacholride is not. ***Imagine that all the chloride ions have 3 sets of lone pairs around each of them. Intermolecular forces can explain why CCl4 boils at 77ºC while CBr4 boild at 190ºC. Bromide ions are much larger than chloride ions, meaning that they possess many more electrons. As a result, CBr4 is intermolecularly connected by London dispersion forces, caused by the occasional shifting of electrons. Therefore, much more energy is needed to break up the molecules, as a result of these intermolecular forces. Upon looking at this problem, you may be very perplexed. However, the answer is extremely understandable. First, the sodium present in the former compound allows for very easy solubility. Secondly, I2 has a covalent bond while NaI has an ionic one. Ionic compounds can ionize in water, but covalent compounds are in molecular form, with bonds much stronger than those of ions, so they do not break up in aqueous solutions. As you can see, the nitrite ion has resonance forms, so the N-O bonds even out; therefore, they are equal. However, the nitrous acid doesn't have resonance forms because one, it is an acid (the H+ is not bonded covalently, so the H-O bond must stay together), and two, this structure is very stable (formal charge). Clearly, one N-O bond is single, and the other double, which is shorter because the atoms have to get closer together. To answer this question, we need to rack our brains for beginning of the year material. In this case, we need to remember orbitals. Sulfur has d orbitals (it is low enough on the periodic table). Oxygen only has p and s orbitals, however. Therefore, it cannot expand the octet to 10 or 12 like sulfur can with the latter two compounds. ***Imagine all of the fluoride ions have three sets of lone pairs around each of them. SbCl3
http://upload.wikimedia.org/wikipedia/commons/e/e5/SbCl3.png
SbCl5
http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Antimon(V)-chlorid.svg/120px-Antimon(V)-chlorid.svg.png
SF2
http://www.chem.purdue.edu/gchelp/molecules/sf2.gif
SF4
http://upload.wikimedia.org/wikipedia/commons/9/94/Sulfur-tetrafluoride-2D.png
SF6
http://upload.wikimedia.org/wikipedia/commons/a/a9/Sulfur-hexafluoride-2D-small.png
OF2
http://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Oxygen_difluoride.svg/169px-Oxygen_difluoride.svg.png
Nitrite
http://upload.wikimedia.org/wikipedia/commons/archive/4/41/20100505000953!Nitrite-ion-lewis-canonical.png
Nitrous Acid
http://draves.org/pix/clip/nitrous-acid2.png Images Cited .. Antimony Trichloride Antimony Pentachloride .. .. .. Nitrite Nitrous Acid ..
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