Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

If Electrons Repel Each Other, Then

  1. Jan 8, 2010 #1
    I am not sure if this is an appropriate area for this topic, so please re-direct if necessary.

    As I understand it, according to Coulomb's Law, Electrons should repel each other (except under certain circumstances such as super cooled as in a superconductor) However, I am having a hard time tying this together with observations of daily life. Perhaps someone might better explain the reasons. Here are a few examples:

    1) Water molecules are made up of two hydrogen and one oxygen atom, all of which have electron fields. Why and how can they "attract" to one another to create the molecule in the first place?

    2) Understanding that the first question may yield an answer of "there are different energy levels for each one when they meet" or something similar, what about water molecule with water molecule? They would consist of the same combination of atoms/electrons, and therefore carry identical energy states, so why does water have such an affinity (attraction) to water?

    3) Obviously water is not the only substance that has an affinity towards itself, so I am a bit confused.

    Thanks for any replies and assistance with this question.

    G
     
  2. jcsd
  3. Jan 8, 2010 #2
    1.) Because there's a distance between the atoms where the energy is minimized. At that distance the nucleus' attraction to the other atoms electrons results in a greater attractive force than the repulsion from just the electrons.

    If you were to plot the energy vs. distance of the atoms it would be something like this: http://filer.case.edu/pal25/image.jpg [Broken]. There would be a bond for energy < 0.

    2.) Your second point is because a water molecule is itself a dipole. So you can think of the molecule as having a positive charge concentration at one location and a negative charge location a little distance away.

    So if you have two water molecules the positive of one dipole and the negative of another dipole would be attracted if they were aligned properly.
     
    Last edited by a moderator: May 4, 2017
  4. Jan 8, 2010 #3

    DaveC426913

    User Avatar
    Gold Member

    What I think you're looking for is why a hydrogen atom (which is surrounded by -ive electrons) and an oxygen atom (which is also surrounded by -ive electrons) would attract.

    Here's the nutshell: Electron shells like to be filled, and will share electrons with other atoms to do so. This makes them stick together.

    The first, innermost electron shell of every atom can hold 2 electrons. The next outer shell can hold 8 electrons.

    Hydrogen has only one electron (in order to be electrically neutral: same # of +s as -s); its electron shell is filled when there are two electrons in it. So, despite being electrically neutral, its normal state has a sort of an electron "hole" that wants to be filled.

    Oxygen has 8 electrons (electrically neutral with same number of +s as -s). These 8 electrons are distributed with 2 in the inner shell and 6 in the outer shell. The outer shell needs 8 to be filled. That leaves it with a sort of 2 holes.

    If 1 oxygen and 2 hydrogen atoms are put near each other and given a little bit of a kick (such as a spark or flame), they will very happily get together and share their 8 electrons. This leaves each H and the O with effectively-filled shells. This state is low energy, meaning it will take a fair bit of energy (such as an electric current) to tear them apart again.
     
    Last edited: Jan 8, 2010
  5. Jan 9, 2010 #4

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    And I should also correct this. Even in a superconductor, the electrons STILL repel each other. Their ability to form bound pairs is NOT because they stop repelling each other, but it is due to all the surrounding ions of the solid that produced the "glue". In other words, a gas of free electron would not be able to form such bound pairs without an external help (either via phonons, or external magnetic fields).

    Zz.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook