What is chemical decomposition in the context of a crystal or amorphous solid?












4














The IUPAC Gold Book definition of chemical decomposition is:




The breakdown of a single entity (normal molecule, reaction intermediate, etc.) into two or more fragments.




That is a very general definition, but I am not sure if it is supposed to be this inclusive. For example, think of a diamond crystal. It is a single entity. Now if chemical decomposition occurs, it can break down into multiple fragments. These fragments are not defined more closely, so it could be that the fragments are single C atoms, polyatomic C molecules... or even diamond fragments again.



In this sense, simply cutting or polishing a diamond would be a special case of chemical decomposition. This seems quite absurd to me. So the question is: Is chemical decomposition really that broad, or is there some better definition that is more commonly used in chemistry? It seems to me that the intuitive definition of chemical decomposition would be that a molecule is broken into smaller fragments, while a crystal or an amorphous solid would need to be broken into non-crystalline (non-amorphous) fragments in order for it to be considered chemical decomposition. Otherwise it's just cutting!



The question is relevant to me because I am writing my PhD thesis on laser-induced breakdown spectroscopy. The "breakdown" in the name of the technique refers to a chemical breakdown, which is the same as chemical decomposition. Usually, solid samples are analyzed, in which case some material from the sample surface is removed by laser ablation. Laser ablation is basically the same as laser-induced breakdown, if you look at the definitions. So there is some confusion on the terminology in general, and I want to unravel it as good as possible in my theory chapter.



Thank you very much for your input!



(Note: By the way, some non-IUPAC definitions I have found for chemical decomposition also confusingly define it as relating to compounds. As far as I know, the definition of a compound excludes crystals and amorphous solids, but it also excludes homonuclear molecules. So this definition seems way too exclusive, because it makes sense that decomposition can also occur for homonuclear molecules.)






terminology decomposition







share|improve this question





























    4














    The IUPAC Gold Book definition of chemical decomposition is:




    The breakdown of a single entity (normal molecule, reaction intermediate, etc.) into two or more fragments.




    That is a very general definition, but I am not sure if it is supposed to be this inclusive. For example, think of a diamond crystal. It is a single entity. Now if chemical decomposition occurs, it can break down into multiple fragments. These fragments are not defined more closely, so it could be that the fragments are single C atoms, polyatomic C molecules... or even diamond fragments again.



    In this sense, simply cutting or polishing a diamond would be a special case of chemical decomposition. This seems quite absurd to me. So the question is: Is chemical decomposition really that broad, or is there some better definition that is more commonly used in chemistry? It seems to me that the intuitive definition of chemical decomposition would be that a molecule is broken into smaller fragments, while a crystal or an amorphous solid would need to be broken into non-crystalline (non-amorphous) fragments in order for it to be considered chemical decomposition. Otherwise it's just cutting!



    The question is relevant to me because I am writing my PhD thesis on laser-induced breakdown spectroscopy. The "breakdown" in the name of the technique refers to a chemical breakdown, which is the same as chemical decomposition. Usually, solid samples are analyzed, in which case some material from the sample surface is removed by laser ablation. Laser ablation is basically the same as laser-induced breakdown, if you look at the definitions. So there is some confusion on the terminology in general, and I want to unravel it as good as possible in my theory chapter.



    Thank you very much for your input!



    (Note: By the way, some non-IUPAC definitions I have found for chemical decomposition also confusingly define it as relating to compounds. As far as I know, the definition of a compound excludes crystals and amorphous solids, but it also excludes homonuclear molecules. So this definition seems way too exclusive, because it makes sense that decomposition can also occur for homonuclear molecules.)






    terminology decomposition







    share|improve this question



























      4












      4








      4







      The IUPAC Gold Book definition of chemical decomposition is:




      The breakdown of a single entity (normal molecule, reaction intermediate, etc.) into two or more fragments.




      That is a very general definition, but I am not sure if it is supposed to be this inclusive. For example, think of a diamond crystal. It is a single entity. Now if chemical decomposition occurs, it can break down into multiple fragments. These fragments are not defined more closely, so it could be that the fragments are single C atoms, polyatomic C molecules... or even diamond fragments again.



      In this sense, simply cutting or polishing a diamond would be a special case of chemical decomposition. This seems quite absurd to me. So the question is: Is chemical decomposition really that broad, or is there some better definition that is more commonly used in chemistry? It seems to me that the intuitive definition of chemical decomposition would be that a molecule is broken into smaller fragments, while a crystal or an amorphous solid would need to be broken into non-crystalline (non-amorphous) fragments in order for it to be considered chemical decomposition. Otherwise it's just cutting!



      The question is relevant to me because I am writing my PhD thesis on laser-induced breakdown spectroscopy. The "breakdown" in the name of the technique refers to a chemical breakdown, which is the same as chemical decomposition. Usually, solid samples are analyzed, in which case some material from the sample surface is removed by laser ablation. Laser ablation is basically the same as laser-induced breakdown, if you look at the definitions. So there is some confusion on the terminology in general, and I want to unravel it as good as possible in my theory chapter.



      Thank you very much for your input!



      (Note: By the way, some non-IUPAC definitions I have found for chemical decomposition also confusingly define it as relating to compounds. As far as I know, the definition of a compound excludes crystals and amorphous solids, but it also excludes homonuclear molecules. So this definition seems way too exclusive, because it makes sense that decomposition can also occur for homonuclear molecules.)






      terminology decomposition







      share|improve this question















      The IUPAC Gold Book definition of chemical decomposition is:




      The breakdown of a single entity (normal molecule, reaction intermediate, etc.) into two or more fragments.




      That is a very general definition, but I am not sure if it is supposed to be this inclusive. For example, think of a diamond crystal. It is a single entity. Now if chemical decomposition occurs, it can break down into multiple fragments. These fragments are not defined more closely, so it could be that the fragments are single C atoms, polyatomic C molecules... or even diamond fragments again.



      In this sense, simply cutting or polishing a diamond would be a special case of chemical decomposition. This seems quite absurd to me. So the question is: Is chemical decomposition really that broad, or is there some better definition that is more commonly used in chemistry? It seems to me that the intuitive definition of chemical decomposition would be that a molecule is broken into smaller fragments, while a crystal or an amorphous solid would need to be broken into non-crystalline (non-amorphous) fragments in order for it to be considered chemical decomposition. Otherwise it's just cutting!



      The question is relevant to me because I am writing my PhD thesis on laser-induced breakdown spectroscopy. The "breakdown" in the name of the technique refers to a chemical breakdown, which is the same as chemical decomposition. Usually, solid samples are analyzed, in which case some material from the sample surface is removed by laser ablation. Laser ablation is basically the same as laser-induced breakdown, if you look at the definitions. So there is some confusion on the terminology in general, and I want to unravel it as good as possible in my theory chapter.



      Thank you very much for your input!



      (Note: By the way, some non-IUPAC definitions I have found for chemical decomposition also confusingly define it as relating to compounds. As far as I know, the definition of a compound excludes crystals and amorphous solids, but it also excludes homonuclear molecules. So this definition seems way too exclusive, because it makes sense that decomposition can also occur for homonuclear molecules.)






      terminology decomposition




      terminology decomposition






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited yesterday

























      asked yesterday









      Spectrosaurus

      385




      385






















          1 Answer
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          active

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          4














          When it comes to non-molecular solids such as glass, metal or diamond, "a single entity" is in fact the formula unit, the concept identical to a "molecule" for, well, molecular compounds. Both formula unit and molecule are the smallest portion of a substance that preserves its chemical properties. As long as the formula unit remains the same, there is no chemical decomposition to speak of.



          However, this doesn't mean that there is no chemical processes that can be initiated mechanically. An entire branch, mechanochemistry deals with them. As for laser ablation, I think you are basically introducing a secondary phase, a thin film of another substance (for example, metal oxide) on the surface.



          One more practical example I can think of: for a single-crystal diffraction experiment one has to use a 3D crystal (in a sense that it shouldn't be a 2D plate for the proper absorpton correction) with linear dimensions not exceeding fractions of a millimeter. For the probe preparation a crystallographer often has to literally cut the crystals with a special scalpel under the microscope. However, the resulting crystal structure doesn't depend on how many cuts and in what direction the crystallographer did. The x-rays though, can alter the structure of some sensitive molecular crystals (often biological samples, proteins), but this is another story.






          share|improve this answer



















          • 1




            Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
            – Spectrosaurus
            yesterday












          • This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
            – andselisk
            yesterday












          • Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
            – Spectrosaurus
            yesterday










          • Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
            – andselisk
            yesterday











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          When it comes to non-molecular solids such as glass, metal or diamond, "a single entity" is in fact the formula unit, the concept identical to a "molecule" for, well, molecular compounds. Both formula unit and molecule are the smallest portion of a substance that preserves its chemical properties. As long as the formula unit remains the same, there is no chemical decomposition to speak of.



          However, this doesn't mean that there is no chemical processes that can be initiated mechanically. An entire branch, mechanochemistry deals with them. As for laser ablation, I think you are basically introducing a secondary phase, a thin film of another substance (for example, metal oxide) on the surface.



          One more practical example I can think of: for a single-crystal diffraction experiment one has to use a 3D crystal (in a sense that it shouldn't be a 2D plate for the proper absorpton correction) with linear dimensions not exceeding fractions of a millimeter. For the probe preparation a crystallographer often has to literally cut the crystals with a special scalpel under the microscope. However, the resulting crystal structure doesn't depend on how many cuts and in what direction the crystallographer did. The x-rays though, can alter the structure of some sensitive molecular crystals (often biological samples, proteins), but this is another story.






          share|improve this answer



















          • 1




            Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
            – Spectrosaurus
            yesterday












          • This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
            – andselisk
            yesterday












          • Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
            – Spectrosaurus
            yesterday










          • Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
            – andselisk
            yesterday
















          4














          When it comes to non-molecular solids such as glass, metal or diamond, "a single entity" is in fact the formula unit, the concept identical to a "molecule" for, well, molecular compounds. Both formula unit and molecule are the smallest portion of a substance that preserves its chemical properties. As long as the formula unit remains the same, there is no chemical decomposition to speak of.



          However, this doesn't mean that there is no chemical processes that can be initiated mechanically. An entire branch, mechanochemistry deals with them. As for laser ablation, I think you are basically introducing a secondary phase, a thin film of another substance (for example, metal oxide) on the surface.



          One more practical example I can think of: for a single-crystal diffraction experiment one has to use a 3D crystal (in a sense that it shouldn't be a 2D plate for the proper absorpton correction) with linear dimensions not exceeding fractions of a millimeter. For the probe preparation a crystallographer often has to literally cut the crystals with a special scalpel under the microscope. However, the resulting crystal structure doesn't depend on how many cuts and in what direction the crystallographer did. The x-rays though, can alter the structure of some sensitive molecular crystals (often biological samples, proteins), but this is another story.






          share|improve this answer



















          • 1




            Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
            – Spectrosaurus
            yesterday












          • This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
            – andselisk
            yesterday












          • Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
            – Spectrosaurus
            yesterday










          • Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
            – andselisk
            yesterday














          4












          4








          4






          When it comes to non-molecular solids such as glass, metal or diamond, "a single entity" is in fact the formula unit, the concept identical to a "molecule" for, well, molecular compounds. Both formula unit and molecule are the smallest portion of a substance that preserves its chemical properties. As long as the formula unit remains the same, there is no chemical decomposition to speak of.



          However, this doesn't mean that there is no chemical processes that can be initiated mechanically. An entire branch, mechanochemistry deals with them. As for laser ablation, I think you are basically introducing a secondary phase, a thin film of another substance (for example, metal oxide) on the surface.



          One more practical example I can think of: for a single-crystal diffraction experiment one has to use a 3D crystal (in a sense that it shouldn't be a 2D plate for the proper absorpton correction) with linear dimensions not exceeding fractions of a millimeter. For the probe preparation a crystallographer often has to literally cut the crystals with a special scalpel under the microscope. However, the resulting crystal structure doesn't depend on how many cuts and in what direction the crystallographer did. The x-rays though, can alter the structure of some sensitive molecular crystals (often biological samples, proteins), but this is another story.






          share|improve this answer














          When it comes to non-molecular solids such as glass, metal or diamond, "a single entity" is in fact the formula unit, the concept identical to a "molecule" for, well, molecular compounds. Both formula unit and molecule are the smallest portion of a substance that preserves its chemical properties. As long as the formula unit remains the same, there is no chemical decomposition to speak of.



          However, this doesn't mean that there is no chemical processes that can be initiated mechanically. An entire branch, mechanochemistry deals with them. As for laser ablation, I think you are basically introducing a secondary phase, a thin film of another substance (for example, metal oxide) on the surface.



          One more practical example I can think of: for a single-crystal diffraction experiment one has to use a 3D crystal (in a sense that it shouldn't be a 2D plate for the proper absorpton correction) with linear dimensions not exceeding fractions of a millimeter. For the probe preparation a crystallographer often has to literally cut the crystals with a special scalpel under the microscope. However, the resulting crystal structure doesn't depend on how many cuts and in what direction the crystallographer did. The x-rays though, can alter the structure of some sensitive molecular crystals (often biological samples, proteins), but this is another story.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited yesterday

























          answered yesterday









          andselisk

          13.5k646100




          13.5k646100








          • 1




            Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
            – Spectrosaurus
            yesterday












          • This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
            – andselisk
            yesterday












          • Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
            – Spectrosaurus
            yesterday










          • Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
            – andselisk
            yesterday














          • 1




            Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
            – Spectrosaurus
            yesterday












          • This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
            – andselisk
            yesterday












          • Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
            – Spectrosaurus
            yesterday










          • Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
            – andselisk
            yesterday








          1




          1




          Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
          – Spectrosaurus
          yesterday






          Thank you, this sounds very reasonable and is something I had not thought of. The definition of a chemical entity is not given by IUPAC, but your interpretation as only relating to the formula unit probably makes the most sense. One unrelated question about the "phase" - I understand it correctly that a mixture of NaCl and KCl, for example, has a NaCl phase and a KCl phase? Or does a phase need to be physically connected so that a homogeneous mixture in fact contains hundreds of small NaCl and KCl phases?
          – Spectrosaurus
          yesterday














          This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
          – andselisk
          yesterday






          This depends on what mixture you are talking about. A mechanical mix of both salts would indeed have 2 phases. However, a system of molten salts with an arbitrarily chosen composition $ce{Na_xK_{1-x}Cl}$ ($0leq xleq 1$) is homogeneous all right (single phase, see e.g. this NaCl-KCl phase diagram).
          – andselisk
          yesterday














          Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
          – Spectrosaurus
          yesterday




          Thank you, this is much appreciated! Yes, I was talking about a mechanical mix, because I was wondering whether several independent grains of NaCl would be considered the same "phase" in a mechanical mixture with something else. (From your reply, I get that the answer is "yes".)
          – Spectrosaurus
          yesterday












          Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
          – andselisk
          yesterday




          Yep, if you take table salt and pour the powder of potassium chloride in, then thoroughly mix them, it's still considered a two-phase system. However, if you increase the temperature enough (say, up to 700 °C, see the phase diagram) and cool the molten salts down, you form a new chemical compound (single phase). This is not always the case and you always have to check the phase diagram first.
          – andselisk
          yesterday


















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          Has there ever been an instance of an active nuclear power plant within or near a war zone?

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          36 3 The question Has there ever been a military combat going on around an active (running or in outage but not decommissioned) commercial nuclear power plant? Or dangerously near it? If yes, how did the plant and its personnel fare in such situation? Why I ask Let's assume for the scope of this question modern commercial nuclear power plants (CANDU, PWR, BWR of generation II plus all of gen III and newer) are usually reasonably safe to operate given that the engineering has been done right and there is a whole cohort of very well trained personnel on-site at all times, well rested and with considerable resources on their hands. Things hard to get with an armed conflict like the recent Syrian war raging around. I can't seem to find any reference or a comprehensive article about this, hence this question.
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