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How Come Neutral Atoms Attract?
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Two forces keep everything in the universe together. Without either, there would be no Solar System, no Sun and no Earth. One is gravity and it always attracts. The Earth attracts every rock, person, bird and airplane. For the force of gravity to be significant, it requires large mass, such as the Earth or Moon. The other force is electrostatic. As you discovered earlier, Coulomb’s force can be attractive or repulsive. The stickiness between molecules is due to electrostatic attraction.
Suppose it's all electrostatic attraction...
OK, one can imagine that the same way charged balloons stick together, atoms stick to each other with electrostatic attractive force. But if all atoms have electrostatic attraction, why do they have different stickiness?
Atoms are neutral. If so, how can they attract?
Well, it is a good question indeed. All atoms have an equal number of protons and electrons. The negative charge of all electrons cancels the positive charge of the protons. Atoms have no electrical charge. They are neither positive nor negative. They are balanced.
Still, there is one interesting detail about the distribution of electrons. The electron cloud fluctuates, which means the cloud shifts relative to the nucleus. The shift is somewhat like a pendulum, but random. Start simulations (below) to explore what the "shifting" does to the balance of charges. Do you think they still cancel each other out?
What have we discovered?
The electron cloud of all atoms is constantly shifting, affecting the symmetry of the electro distribution around the atom.
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<font size="4" face="Verdana">Let's suppose that different atoms have
different electrostatic attractions. Will this explain why water is liquid
but air is a gas under the same conditions? Let's explore this with a
model of a mixture of two different types of atoms and assign them
different electrostatic attraction. </font>
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<font size="4" face="Verdana">To cool or heat the mixture, use the
buttons below. If you feel like it is time to rain, check the "allow
gravity" box.</font>
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Take three snapshots of the atom in different "shifting" states.
Annotate the images to indicate where you think the charges are
cancelled and where they are not.
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<font face=Verdana size=4>Can the "shifting" of the electron cloud make atoms sticky?
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