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This might seem like a stupid question but please bear with me.

I've always studied and read that the molecules at the surface have higher energy than those at the interior and the explanation is also justified since very less energy is required to break them apart on surface so they must be at high energy. The molecules at the surface tend to stick to molecules of other substances to bring the energy level down(Not always but mostly like glass and water).

Here comes the question:

When we break a solid into molar chunks or grind it down to a powder, every chunk's surface energy must also be increased and they should also stick to other chunks to bring the energy down. And since their inter molecular bond is strong why don't they again stick together and form a solid piece again.

Neeraj Sharma
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1 Answers1

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You're absolutely correct that the surface molecules have a relatively high energy. They generally respond by

  1. Oxidizing or sulphurizing or otherwise chemically reacting with the air.
  2. Adsorbing a coating of atmospheric contamination—e.g., hydrocarbons.
  3. Reconstructing.

In metals that don't oxidize at room temperature, such as gold, it's not too hard to push aside the dirt (with a little ultrasonic scrubbing, for example) and reform strong metal-to-metal bonds. This is how wire bonds are created. See also cold welding.

Chemomechanics
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