Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: peterpan1372 on September 16, 2017, 06:55:55 PM
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Which one of the following covalent substances could exist as a giant structure?
A SiCl4
B SiO2
C ICl
D Cl2O
E H2S
F CF4
I seriously don't know which one to choose... I know that giant structures have very high melting points and variable conductivity, but do not know why/or why not everyone of them could be right or wrong..
Appreciating any *delete me*
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Now this is a tough one. What would you consider a giant structure? What wouldn't a giant structure be made of? Ever see a a liquid or gas be a structure?
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What would you consider a giant structure? What wouldn't a giant structure be made of? Ever see a a liquid or gas be a structure?
to first question: I already stated.
to second and third: I dont know which one of them could be gases or liquids...
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This question makes almost no sense. I think I know what they are getting at, and what the answer probably is, but the concept is so ridiculous I feel silly even trying.
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and what is the concept?
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Does the BMAT actually use these words
giant structure
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I think they mean a polymeric structure
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Here, lets go through the posibilities in terms of the bonds they make.
A SiCl4
B SiO2
C ICl
D Cl2O
E H2S
F CF4
Only one of these is not "happy" existing as a molecule, so it is likely only a repeat unit in a larger structure. Can you identify which one of these stands out in that regard? Think about the number of bonds each atom likes to have.
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what do you mean?
what does Cl2O , for example, like?
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Have you learned about oxidation numbers?
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Cl->-1 and O ->-2
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Well yes, ok. Though that is in fact the funkiest example, since Cl is actually in the +1 oxidation state for that compound. Don't ask why its not O +2 Cl -1, it has to do with ionization energies I think.
Aside from that, all those compounds are generally in their normal oxidation states. Do you see one that if you drew the bonding out, would be very amenable to making bonds with other versions of itself?
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I would say SIO2... reason: since SI has a charge of +4 and O -2, that wouldn't equal it out... right?
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Correct. And the term we are really dealing with, as opposed to 'Giant structure" is "network covalent bonding." I had never heard this term "giant structure" before, and googling it leads to rather less technical sites than I would usually prefer to use. It really threw me off.
https://en.wikipedia.org/wiki/Network_covalent_bonding
Also, for petes sake, its Si for silicon, not SI.
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yeah, but why B)? why do pairs which don't equal them out exist as a "giant structure?"
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In chemistry at your level, sometimes you just have to settle for learning traits without delving too deeply the origins of rules, because the answers require a deep understanding of physical chemistry.
Oxygen likes to form two bonds, and silicon, like carbon, likes to form four. However unlike carbon, silicon does not like to form double bonds because it is a bigger atom and the p orbitals responsible for forming pi bonds are more diffuse, and so overlap between p orbitals on adjacent nuclei is poor. For this reason, CO2 is a small molecular gas with formula O=C=O, whereas silica, which has the same type of (SiO2) forms an extended structure characterized by single bonds between silicon and oxygen atoms. It is the only structure available that minimizes the number of pi bonds formed with silicon atoms.
Looking at your other options: (A) can't form easily an extended structure because halogens like chlorine typically (though not always) only bond 1 time each, so SiCl4 is a small molecule. This logic also extends to (C) and (D). (E) is likewise excluded because hydrogen usually only bonds once as well, and (F) involves fluorine, another halogen that is only available for a single bond to another atom. So with the exception of (B), all do not offer the ability to form extended structures because to do so would involve more bonds than the atoms involved would typically be happy to form.
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As I understood it: you mean because Si has a higher oxidation number, it forms more likely a double bond becasue of its higher number of free electrons, making it more solid?
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What would you consider a giant structure? What wouldn't a giant structure be made of? Ever see a a liquid or gas be a structure?
to first question: I already stated.
to second and third: I dont know which one of them could be gases or liquids...
You could look up which of these substances is a gas or liquid at room temperature.
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on test day, you have max. 15 sec to solve this question without internet, calculator etc...
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As I understood it: you mean because Si has a higher oxidation number, it forms more likely a double bond becasue of its higher number of free electrons, making it more solid?
No, the formal oxidation number of silicon has very little to do with it. And I already told you that silicon does not form double bonds easily. Honestly, though you can arrive at the correct answer of B by process of elimination. All the other options involve halogens or hydrogen atoms, which only bond once, and there's no way to make long extended networks of atoms as a result.
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isn't there another way to get to the answer quickly?
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or other question: is there a quick way to know if a substance is made of gas, liquid, or is solid?
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you also stated: (E) is likewise excluded because hydrogen usually only bonds once as well, and (F) involves fluorine, another halogen that is only available for a single bond to another atom.
That is what I meant. Of course, when atoms bond once it is not a strong bond. But when they bond with atoms which have excessive bonds available, this bond is going to be more solid...
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That is what I meant. Of course, when atoms bond once it is not a strong bond. But when they bond with atoms which have excessive bonds available, this bond is going to be more solid...
I am not sure what you mean. Double bonds are stronger than single bonds; however, the C-F bond is a single bond, and it is quite strong.
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what I mean is: obviously, Si has a higher electronic configuration than O. So the molecule is hence going to be more stronger than the rest since it has electrons available that it hasn't used.
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With apologies, peterpan1372, it is evident that you really lack an understanding of the most elementary concepts in chemistry and I don't think there's much I can do to help you further. I don't regard this forum as a replacement for basic instruction in your courses - we can't teach you all of chemistry here.
I would strongly suggest you find a personal tutor or ask your professor/instructor for additional intensive help outside the classroom.
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Don't get me also wrong, but tutors are helpless. Further, I don't have the money for one. I just want to, really short and understandable, why SiO2 is the right answer if one can not dispute with oxidation numbers...
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I just want to, really short and understandable, why SiO2 is the right answer if one can not dispute with oxidation numbers...
Yes but what about the next question, and the next after that? You have posted many questions in the last week or so. Virtually all demonstrate a lack of understanding of basic principles which are spelled out in any introductory textbook. Please talk to your professor if you feel this material is not being covered, this is their job. We just do this with bits and pieces of our free time.
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of course, I appreciate it, but I just want a quick understandable explanation of what you wrote - nothing else.
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a quick understandable explanation of what you wrote
Would be based on ideas you don't know - and as such would be completely useless to you.
You need to start from the beginning. You can't learn trying to solve a test in which every question - while not very hard - uses many different concepts combined. You need to learn these concepts separately before using them, and that's something that you can do only by following a textbook (or a lecture) that introduces them in some logical order, adding new steps based on what you have learned earlier.
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which book(s) would you recommend?
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Literally any "Introduction to Chemistry" first year university textbook.
https://www.google.com/search?q=introduction+to+chemistry+textbook&rlz=1C1CHBF_enUS712US712&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwiIx6K48LHWAhXr6YMKHeEMCvAQsxgIKQ&biw=1280&bih=918
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but still I want to know the answer why SiO2 is a giant molecule and the rest not...
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Corribus has already given an extremely precise correct answer
Oxygen likes to form two bonds, and silicon, like carbon, likes to form four. However unlike carbon, silicon does not like to form double bonds because it is a bigger atom and the p orbitals responsible for forming pi bonds are more diffuse, and so overlap between p orbitals on adjacent nuclei is poor. For this reason, CO2 is a small molecular gas with formula O=C=O, whereas silica, which has the same type of (SiO2) forms an extended structure characterized by single bonds between silicon and oxygen atoms. It is the only structure available that minimizes the number of pi bonds formed with silicon atoms.
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So, why did you brought up the oxidation number when it has nothing to do with the question @wildfyr ?
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To help you see the point about how many bonds a given materials "likes" to make, as Corribus pointed out in his first sentence.
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is there also another way to know whether a molecule like to form sigma or pi bonds without pre-knowledge?
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is there also another way to know whether a molecule like to form sigma or pi bonds without pre-knowledge?
Yes, it is based on basic concepts of quantum chemistry, as it depends on which atomic orbitals are involved in the bond. No, I won't get into details, as it is part of the basic chemistry course we told you to follow.
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As I understood it: Silicon has a electronic configuration of 1s^2 2s^2 2p^6 3s^2 3p^2
in contrast, carbon has 1s^2 2s^2 2p^8 ... based on that, Si is more inclined to build sigma bonds because it has more s orbitals filled than p orbitals, or?
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if that is right, why is SiO2 the right answer and not SiCl4 ? because of the fact that all electrons are "used up" at SiCl4? (Hence, it would have space free to "stretch" itself like in Si02 ?)
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Because unlike oxygen, which tends to bond twice, chlorine tends to bond only one time. The reason for these numbers of bonds is related to the respective # of valence electrons in each atom and the "desire" of the atom to have eight (or two, in the case of first row) electrons in the valence shell - something called the octet rule. Your general chemistry text should have a lot to say about valence electrons, the octet rule, and bonding. I suggest you read these chapters carefully - learning these concepts is enough to understand fully how to answer this question, and, frankly, a lot of general chemistry. If you don't have a general chemistry book you can find plenty of helpful videos online - e.g., https://www.youtube.com/watch?v=gsvR4AZGRSk. These are concepts too detailed and extensive to teach to you in an online forum.
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As I understood it: Silicon has a electronic configuration of 1s^2 2s^2 2p^6 3s^2 3p^2
in contrast, carbon has 1s^2 2s^2 2p^8 ... based on that, Si is more inclined to build sigma bonds because it has more s orbitals filled than p orbitals, or?
is that right?
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No.
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what is wrong with the explanation?
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Why don't you read about valence electrons in your chemistry textbook and tell us what you think is wrong with what you wrote.
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Chlorine = 1 valnce electrone. we have 4 Cl in SiCl4
O= 2 valnece electrons. We have 2 of them, making it here 2 O's too.
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No, that's not how many valence electrons those atoms have. Which means you probably didn't read about valence electrons. If you don't invest time in learning the basic principles, you have no hope to answer questions like this correctly. Moreover, if you won't invest time in yourself, why should we invest time in you?
I think I'm done here.
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I'd say that we all are. *Topic Locked*