Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: katieHaylor on 08/09/2017 17:43:07
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Akhilesh says:
Can we increase or decrease size of objects by increasing or decreasing the space between atoms?
What do you think?
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For most materials, if you heat the material, the vibrations of the atoms increases, which increases the average distance between the atoms, causing the material to expand.
This is most dramatically demonstrated when you heat a liquid past its boiling point. For example, water expands by about a factor of 1,000 when it turns into a vapor, because the space between the atoms is greatly increased.
There are some unusual materials which sometimes disobey this general rule; for example water shrinks as you increase the temperature from 0C to 4C. But otherwise it obeys this rule of hotter makes it expand.
There are also some materials that have been designed to hardly expand or contract as you change the temperature (at least, over a limited range of temperatures). These are used in the manufacture of precision scientific instruments like telescopes.
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Yes! (but with so many limitations, that you will probably find it so limiting that I should have said no...)
In many cases the properties (or cohesion) of the object are so changed that you could say it is not just a bigger version of itself. The amount of space that you can insert between atoms without changing the properties of the object depends very strongly on the amount of space already there:
Atoms that are less than about 3 Å (3x10–10 meters) away from another atom (center to center) are likely to be interacting (strongly) with their nearest neighbors, and their neighbors neighbors, and their neighbors neighbors neighbors, etc. (chemists call this "bonding" or intramolecular interactions). Changing the distance between bonded atoms by even 1-2% (10–12 meters) can have profound effects on the properties of the material, and probably comes with a very steep energy penalty (think of it like pulling or pushing on a very stiff spring, which incidentally is exactly how a spring works!)
Atoms that naturally have more like a 5–10 Å distance to their nearest neighbor will only interact weakly with this neighbor (chemists call this intermolecular interactions). There will be a little bit of springiness keeping the other atom away, and a weak attraction keeping it from floating away completely, but there is (for lack of a better phrase) more wiggle room here, and you can potentially increase these distances by several percent before seeing tremendous differences in the properties (though there are many cases where the wiggle room is much less). This can be observed in the thermal expansion of liquids (like how an old fashioned mercury or alcohol thermometer works!).
Atoms with more than 20 Å separation from their nearest neighbor can be though of as being isolated. The distance is so great that the interaction is negligible. (chemists call this a gas) In this case, it is easy to expand the distance between the atoms, it still takes energy, but it is easy to expand the size of a gas by orders of magnitude. (This is how things like hot air balloons and vacuum pumps work). We can argue about whether an object can be made out of gas or not, but I would point to air bubbles, atmospheric systems, and gaseous planets as examples of gaseous "objects"