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Water and atoms

  1. Apr 24, 2003 #1
    Water is a dipole right? Having a slightly positive side and a negative side.

    If this is true, then won't water molecules have a certain arrangement or pattern? Due to the "poles" attracting and repelling?
    Just like how magnets, which when stuck on sticks in a grid format, will self-organize into a certain pattern.

    Why does water expand when it is cooled to a certain temperature(if i remember correctly, it's 4 degrees celsius)? Is it because of its slight positive and negative sides?

    Also since electrons are orbiting the nucleus, when those electrons like move close to each other, won't they repel and cause the outer electron to "fly away"?

    You know how they calculate the overall charge of atoms. If there is an equal number of protons and an equal number of electrons, then the overall charge is zero. Does this imply that the protons's positive charge and the electron's negative charge have the same "force"?

    If they have the same "force", when something, eg. a positive particle, is near the outside of an atom. And the atom has both 5 protons and 5 electrons, won't the atom attract the positive particle? 'Cause the positive particle is nearer to the electron then the protons, so the electrons should exert a stronger attraction force on it then the repulsion force of the protons.
  2. jcsd
  3. Apr 24, 2003 #2
    Go here for a comprehensive guide to water structure:

    How do they move closer? Also stable atoms have their electrons aranged so that they are in stable orbits. But you can't really treat electrons as point objects when considering their interactions in an atom. Really they need to be treated quantum mechanically and then the concept of an electron moving closer is not so meaningful.

    The force between a proton and electron depends on both the protons and electrons charge.
  4. Apr 24, 2003 #3
    Yes, if it's cold enough -- we call it 'ice.' :smile: If it's too hot, there is too much "jumbling" going on for the structure to form, as if you were shaking the grid of magnets.
    Almost right -- if the electrons were equally distributed around the atom, then the close electrons and the far electrons would average and act like they were at the center. But a positive particle nearby will attract the electrons over to its side of the atom, and then attraction will occur. This is referred to variously as a London dispersion force, van der Waals force, induced dipole attraction, etc, depending on the details.
  5. Apr 24, 2003 #4

    Yes, it is because of the negative an positive sides.
    When water cools down (4 degrees or lower), the molecules' average speeds gets down, and the effect of the negative and positive sides become bigger on making the molecules into the grid that you are describing.
    The volume of a certain number of molecules in this grid is bigger than the volume of the same number of molecules when they are moving around without being in a grid form, therefore (And since the number of atoms will not change when the water gets cooled down), the volume of the water will get bigger, or .. it will (in common words), expand.
    Although i personally do not like to call it expand, since it is not exactly like the reason of expanding of other materials with the rise of temprature.

    I hope i helped.
  6. Apr 29, 2003 #5
    Are you implying that protons and electrons have charges which will vary?

    Erm, maybe i didn't make it clear enough or maybe i don't understand. Let's say i have a pure vacuum, no particles disappearing and appearing because of energy fluctuations. I have that same atom(that atom is not attached to anything else), with 5 protons and 5 electrons inside the vacuum. When a lone proton passes nearby the atom, won't it get attracted to an electron? Then when a lone electron passes nearby, won't it then stick onto the proton, which is stuck onto the electron, and this goes on and on and on. Kinda like an alternating pile-up, does this happen?

    Woohoo! I guessed correctly!

    What about prisms and light?

    Is this why all the 7 colours of light combine to form white light when passed through a prism:

    Just imagine a wave, which represents 1 of the colours of light.
    Wave diagrams have those humps and troughs right? Let's say the area of the hump, which is also the area of the trough, for red light is 2x. Blue light has troughs with an area of -1/2x, green light has a hump with an area of 3x, so on and so forth.

    So when the waves, which are in sync and out of sync, converge at the same spot, they interfere destructively and constructively,
    2x + (-1/2x) + 3x + 1/3x + 2/5x + (-1x) + (-8/9x) = 3.34x

    Thus the resultant wave with a hump or trough with an area of 3.34x is white light?

    *the x and coefficients of x mean nothing, just arbitary values.
  7. Apr 29, 2003 #6
    Be glad that it does. If solid water was more dense than liquid water (as is usually the case in nature), life as we know it would probably not exist.

    This anomaly of nature allows ice to float. If it didn't, it would sink to the bottom of the water where the sun would have a hard time melting it, and it would grow larger and larger until there was just a thin layer of water at the surface. Probably not enough for anything but basic life forms.
  8. Apr 30, 2003 #7
    What is the reason for this anomaly?
  9. Apr 30, 2003 #8
    I think it has to do with the crystal latice formation (ice). The water molecules in the crystal pattern occupy about 9% more space than an equal amount of water.
  10. Apr 30, 2003 #9
    I know that. But I don't know, why. That is what I want to know - what phenomenon is responsible for increase in intermolecular distance in 4--0 C interval. I guess, the shape of van-der vaalse potential well. If so, why is the well such?
  11. Apr 30, 2003 #10


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    It's due to the polar moment of the water molecule, thanks to the low electronegativity of the Hs and high electronegativity of the O. This gives the water molecule the capability to form strong dipole-dipole attractions which we call Hydrogen bonds. Each water molecule can form 4 such bonds, thanks to the two H atoms and two lone pairs on the central O. Because of charge repulsion from the other e pairs etc, hydrogen bonds tend to be most stable in a linear geometry, hence the form of the lattice. That help any?
  12. Apr 30, 2003 #11
    I know that. Average intermolecular distance (thus density) is the average distance between centers of oscillating/rotating molecules.

    So my question is: is right side of potential well of a water molecule (surrounded by other water molecules) more steep than left side at 0-4 C interval (=at about 23.5 millielectronvolt from the bottom)? Then indeed the average distance between molecules will DECREASE with increase of amplitude of oscillation. If the shape of the well is more conventional (right side is more gentle slope than steep left side), then something else is messing around.

    And if the potential well is indeed anomalous around 0-4 C, why is that? And why only in 0-4 C energy range?
    Last edited by a moderator: Apr 30, 2003
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