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Chemistry: General Properties of Nonmetals

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  • Type: Video Tutorial
  • Length: 6:32
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 69 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Nonmetals (12 lessons, $19.80)
Chemistry: Nonmetals and Hydrogen Introduction (2 lessons, $3.96)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/chemistry. The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more.

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

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Thinkwell
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A periodic table can be broken up into pieces and those pieces are the main group, which are the yellow elements, here on the left, and the purple things here on the right, including helium and I don't know why helium is yellow here. Then the transition series, which are the elements in orange and then down at the bottom the green elements, are the lanthanides and the actinides. What we are going to focus on here is we are going to focus on the nonmetals in the periodic table. The nonmetals are located over to the right and sort of up high in the periodic table, so for instance, fluorine and oxygen and neon and chlorine those are all nonmetals. They have the properties of not being electrically conductive the way metals are electrically conductive, so they are insulators. They don't conduct heat very well; they are basically everything that the metals aren't.
Now as you might imagine, there is a intermediate regime, where you have metals, and you have nonmetals, that somewhere in between there are going to be some things that behave somewhat in between metals and nonmetals and we call those species metalloids and those are typically taken to be boron, silicon, germanium, arsenic, antimony, tellurium and acetine. You can see that they make sort of a diagonal here, and the diagonal makes sense because things become more metallic as you go down the periodic table. For instance, lead is a metal, but carbon is a non-metal and things become more metallic as you go from right to left. Things tend to become more metallic. Okay.
So, what about the nonmetals, can we say? First of all, a lot of the nonmetals tend to be gases, helium, neon, argon, krypton, xenon and radon those are all gases, in addition fluorine and chlorine and oxygen and nitrogen are gases, the bromine is a liquid, and it is one of the few liquids in the periodic table, you know that mercury is also a liquid and that cesium is just about a liquid. I don't even know if there is enough francium in the universe to know whether francium is a liquid, but you might imagine that it is going to be really close to a liquid at room temperature as well. Anyway Iodine is a solid and all the other nonmetals are solids and they have some properties that distinguish them from the metals.
One of the first properties that distinguishes them is that they tend to show many different oxidation states, both positive and negative. To give you an example, carbon in methane is minus four, but carbon in carbon dioxide is plus four, nitrogen and ammonia is minus three, but nitrogen in nitrate is plus five, whereas in contrast for the metals, particularly the main group metals, you only see one oxidation state, potassium is always either plus one or zero, but in its compound it is always plus one. The transition series you see multiple oxidation states, but typically the oxidation states are positive. There are relatively few negative oxidation states, even among the transition series.
If you take a metal and you react it with a nonmetal what do you get? Typically you get an ionic compound; that is, the metals are electro positive so they're relatively willing to give up electrons and the nonmetals are relatively electro negative, they want electrons. So what you have is a transfer of an electron from the metal to the non-metal, like sodium to chlorine to make sodium chloride, which is an ionic species.
In contrast within the main group, nonmetals, what you see as covalent or polar covalent bonding. So a lot of sharing of electrons, not really, really profound differences between electric activities. So for instance phosphorous tri bromide or something like that is a compound from two nonmetal main group elements and what you see is a polar covalent bond, but you don't see any of the characteristics of an ionic species. A solution of boron tri bromide at room temperature is not going to conduct electricity for instance.
What we are going to see is that the properties within families or within columns have a lot in common. So for instance you might imagine that NH[3] is a reasonable compound, PH[3] is a reasonable compound, similarly CH[4] methane and SIH[4], which is silane, so you see a lot of the same sorts of common properties within columns that we have seen elsewhere in the periodic table.
I just want to take a moment to comment on the fact that there is a distinction between elements in the first row, particularly carbon, nitrogen, and oxygen, but to a lesser extent. Boron compared to the rest of the main group nonmetals and that the propensity for pi bonding or multiple bonding. It really dominates the chemistry or at least it is a significant component of the chemistry of carbon nitrogen and oxygen, again to somewhat lesser extent boron. It really is not important down in the rest of the periodic table. It is not that it is not exist, but if you had to decide, you would probably guess that there isn't a lot of multiple bonding in the elements down here, compared to carbon nitrogen and oxygen.
To give you a great example of that, carbon dioxide is a molecular species. It is a trinuclear molecule that is a gas at room temperature. In contrast, silicon dioxide is a solid. You might have thought, okay well they are in the same family, they ought to look real similar, but in fact, silicon dioxide is an extended network solid and is essentially not volatile at all at room temperature. Similarly, N[2] nitrogen in its elemental form is a gas, but phosphorus exists as PH[4] tetrahedral oxygen is the diatomic molecule having an oxygen, oxygen double bond. Nitrogen has a nitrogen, nitrogen triple bond, but when we look at sulfur, sulfur is not S[2]; in fact it is S[8], where we have eight sulfurs in a ring, where we only have sigma bonding. We have only sulfur, sulfur sigma bonds. Sulfur, sulfur double bond is not really important in sulfur, not nearly as important as it is the bonds between oxygen and itself.
What are we going to see? We are going to examine these elements in columns in families and we are going to see a lot of the kinds of trends that you might expect. Similar oxidation states, similar reactivity, but as I mentioned, there is a big difference between the first row and the rest of this table and it makes sense based on the idea that if you have multiple bonding in the 2 p orbitals you get better overlap. So that is why you see multiple bonding up here and much less so as you go down the column in the periodic table.
The Nonmetals
An Introduction and Hydrogen
General Properties of Nonmetals Page [2 of 2]

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