Atomic diffusion is a process whereby the random thermally-activated hopping of atoms in a solid results in the net transport of atoms. For example, helium atoms inside a balloon can diffuse through the wall of the balloon and escape, resulting in the balloon slowly deflating. Other air molecules (e.g. oxygen, nitrogen) have lower mobilities and thus diffuse more slowly through the balloon wall. There is a concentration gradient in the balloon wall, because the balloon was initially filled with helium, and thus there is plenty of helium on the inside, but there is relatively little helium on the outside (helium is not a major component of air). The rate of transport is governed by the diffusivity and the concentration gradient. Properties For alternative meanings see atom (disambiguation). ... A solid is a phase of matter, characterized by resistance to deformation and changes of volume. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Air is a name for the mixture of gases present in the Earths atmosphere. ...

See also

• Kirkendall effect