How come Nacl is not poisonous?

  1. Na is poisonous for us, so is Cl2 (chlorine).
    How come Nacl is not poisonous?
     
  2. jcsd
  3. Borek

    Staff: Mentor

    Compounds have different properties than elements they are made from, period.
     
  4. Elements can be highly reactive- like sodium....It wants to give away one electron like crazy:
    It will donate this electron to almost any other element. Now it is sodium+1, an ion.
    A Chlorine atom is also reactive, but it wants an electron so badly that it usually shares one with another Chlorine atom and is found as Cl2. But this pair is still extremely reactive and will react with nearly any other atom to get more electrons: They then form 2 Chloride ions which are described as Cl single minus. These ions stay the same when dissolved in water, where the Na+ and Cl- disassociate from each other to make salt water. All animals need Na ions to make their bodies and nervous systems operate properly, also Potassium and Magnesium ions.
     
  5. When Nacl is formed electrons are displaced by a very very small distance and new bonds are formed? Is such a small change responsible for such huge difference in properties of the new compound?
     
  6. Borek

    Staff: Mentor

    See explanation by dacarls.

    Yes.
     
  7. dacarls explanation goes deeper than you might think, so take heed of Borek's advice.

    When you ingest salt you are ingesting sodium and chloride ions. These have vastly different properties from the parent atoms or molecules of sodium or chlorine and are no longer bonded together.

    So that small shift of an electron does indeed have huge consequences.

    You may have heard of something similar but reversed with another substance.

    Oxygen.

    The normal molecule O2 is life giving but another form O3 (Ozone) is poisonous, except in very small quantities.

    Worse, the ions from oxygen (there are several types) can cause cancer.

    So it is the reverse since the molecule is beneficial and ion deadly in this case.
     
  8. Ygggdrasil

    Ygggdrasil 1,566
    Science Advisor

    The chemistry of a substance is essentially defined by its electron configuration. If you change the electron configuration, you completely change its reactivity with other substances.
     
  9. [​IMG]
    The process of NaCl making is pretty much like that. Trust me, I saw it with a electroquantum microscope.

    (No, I didn't.)

    You can see how the chloride has one empty slot for another electron. It wants it so bad it decided to steal one from the first element in sight.
    Dialogue balloon are that size because that image wasn't intended for English.

    ^
     
    Last edited: Jan 3, 2013
  10. well... carbon monoxide and nitrogen are isoelectronic. its a bit more subtle; vibrational spectra, which determine thermal stability, depend also on masses. also there's stuff like the isotope effect in superconductors.

    all in all, its very messy but in general its correct =)
     
  11. Ygggdrasil

    Ygggdrasil 1,566
    Science Advisor

    Very good point.
     
  12. DrDu

    DrDu 4,185
    Science Advisor

    The point is that although the electrons are only moved over small distances, the electric fields working are enormous. The reason is Coulombs law stating that the electric field seen by an electron near an ionic core depends on ##1/r^2## where r is the distance of the electron and the center of the ion. As r is a small quantity, the fields are huge.
     
  13. Force are much more stronger in the nucleus. Does it mean displacing a proton by a very-very-very-very small distance will produce dramatic effects?

    What about plank's scale. If sub atomic ( protons, quarks etc. ) particles move by only that much distance or even less distance than that? Will dramatic effects still occur? By dramatic I mean, a huge change in the erstwhile properties.
     
  14. Careful how you put this for you are implying that one zone of space is different from any other.

    One of the most important underlying principles of all science is that primary laws are the same everywhere, ie in every zone of space.
     
  15. I love when people say something isn't poisonous, because how lacking science can be in terms of rigorous definitions is amusing to me.

    One principle of toxicology is that the dose makes the poison. ANYTHING, in a certain concentration, can be said to be "poisonous." In fact, Wikipedia lists the median lethal dose between 3000 and 8000 mg/kg (for tested small rodents). This means that in a sample of small rodents, 50% of them will die when given sodium chloride in an amount between 3000 and 8000 milligrams for every kilogram of body mass.

    It becomes more of a question of biology, but it can be fairly simple to see how a large amount of NaCl might affect a biological system (exempli gratia the human body):

    Let's imagine, for simplicity, that the cytoplasm is an ideal solution. Cell membranes are semipermeable, so we can model the osmotic pressure using the equation [itex]\Pi = i MRT[/itex]. Let's also assume that the LD50 of tested animals from Wikipedia translates decently well to humans. With a 70 kg person (and 8000 mg NaCl per kg body mass) and 5 liters of blood, we get a 1.916 M NaCl solution. Assuming an average internal body temperature of 310.15 K and NaCl to have a van't Hoff factor of 2, we get that the osmotic pressure is [itex]\Pi = iMRT ≈ (2)(1.916)(0.082)(310.15) ≈ 97.57 atm[/itex]. This means that one needs to apply a pressure of 97.57 atm in order to negate osmosis. In essence, cells start to become drained of their internal fluids and begin losing functionality. In other words, death.
     
    Last edited: Jan 4, 2013
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