Did you ever play with a drop of oil on the surface of the broth? Trying to stretch it to a bigger pond? In 1926, Jean Baptiste Perrin got a Nobel prize for this - he measured atom dimensions.
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Perrin's experiment. |
"Dimensions" of atoms can be obtained in many ways but very different
answers
1. In gases, the atomic "dimension" is the distance, at which they start
to push each other in a rather brutal way - their diameters are estimated
with deviations from the perfect-gas equations, when it is impossible to pressurize
more the gas and it condensates. Like the dew in the morning.
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2. In liquids, dimensions of the particles influence the "neighborhood" effects, like the viscosity. Huge molecules, like this polymer, never stop sipping. |
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3. In crystals, atomic diameters are defined as dimensions of elementary cells, visible by the X-rays or electron-beam diffraction. |
Atomic diameters could be also evaluated from the density - if we knew how many atoms were contained in one portion, i.e. in 1 mole of the substance. But we need to know the advocate's Avogadro number, what is also difficult