A question purely for my own curiosity.

I am trying to understand what "holds the atoms in a metal bar" in shape.

A general question about metals, but let's use gold as an example.

Under suitable laboratory conditions

  • if we isolated a single atom of gold
  • and dropped that onto a plate of gold

Would the atom fuse with the plate ?

Would the valence electrons of the single free atom "attract that atom into a bond with the crystal lattice" ?

I did some searching and found this:

Metallic bond, force that holds atoms together in a metallic substance. Such a solid consists of closely packed atoms. In most cases, the outermost electron shell of each of the metal atoms overlaps with a large number of neighbouring atoms. As a consequence, the valence electrons continually move from one atom to another and are not associated with any specific pair of atoms. In short, the valence electrons in metals, unlike those in covalently bonded substances, are nonlocalized, capable of wandering relatively freely throughout the entire crystal. The atoms that the electrons leave behind become positive ions, and the interaction between such ions and valence electrons gives rise to the cohesive or binding force that holds the metallic crystal together.


I can think of a reason why two gold bars wouldn't fuse together when placed together:

  • the irregularity of their surfaces would not permit close enough contact ...
  • (ignoring any surface oxidation)

But I'm curious about the case of a "single free atom".

  • 1
    $\begingroup$ I'm unsure of how to envision "dropping" a singular atom, since at that point the atom will be in motion throughout the apparatus acting as a gas. So in light of my picture of what the physical scenario is, I would say factors such as velocity at time of contact and surface energies will dictate if the single atom would be absorbed into the crystal lattice. Related: physics.stackexchange.com/questions/87107/… $\endgroup$ – J. Ari Aug 3 '17 at 14:37
  • $\begingroup$ I guess you might want to read this: Hevesy, G.; Obrutsheva, A. Nature 1925, 115 (2897), 674–675. DOI: 10.1038/115674a0 and remember the experiment mentioned in all physics textbooks on what happens when lead and gold bars are compressed together. $\endgroup$ – andselisk Aug 3 '17 at 14:41
  • 1
    $\begingroup$ It is common in the semiconductor industry to evaporate metal to form metal layers. $\endgroup$ – MaxW Aug 3 '17 at 14:44
  • 1
    $\begingroup$ Of course, the atom can and will stick to the bar, at least if the surface is clean enough.... Is it as in the case of cold, in vacuum soldering that you have mentioned. $\endgroup$ – Alchimista Aug 3 '17 at 15:25
  • 2
    $\begingroup$ Cold welding does happen as shown in this video: youtube.com/watch?v=mHAhfX7iRjs $\endgroup$ – A.K. Aug 3 '17 at 18:22

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