Editing History of atomic theory (section)

===Brownian motion===
In 1827, the British botanist [[Robert Brown (botanist, born 1773)|Robert Brown]] observed that dust particles inside pollen grains floating in water constantly jiggled about for no apparent reason. In 1905, Einstein theorized that this [[Brownian motion]] was caused by the water molecules continuously knocking the grains about, and developed a mathematical model to describe it. This model was validated experimentally in 1908 by French physicist [[Jean Perrin]], who used Einstein's equations to measure the size of atoms.<ref>{{Cite web |title=The Nobel Prize in Physics 1926 |url=https://www.nobelprize.org/prizes/physics/1926/perrin/lecture/ |access-date=2023-02-08 |website=NobelPrize.org |language=en-US}}</ref>

{| class="wikitable"
|+ Kinetic diameters of various simple molecules
|-
! Molecule !! Perrin's measurements<ref name="Perrin 1909 p. 50">[[#refPerrin1909|Perrin (1909). ''Brownian Movement and Molecular Reality'', p. 50]]</ref> !! Modern measurements
|-
| Helium || 1.7 × 10<sup>−10</sup> m || 2.6 × 10<sup>−10</sup> m
|-
| Argon || 2.7 × 10<sup>−10</sup> m || 3.4 × 10<sup>−10</sup> m
|-
| Mercury || 2.8 × 10<sup>−10</sup> m || 3 × 10<sup>−10</sup> m
|-
| Hydrogen || 2 × 10<sup>−10</sup> m || 2.89 × 10<sup>−10</sup> m
|-
| Oxygen || 2.6 × 10<sup>−10</sup> m || 3.46 × 10<sup>−10</sup> m
|-
| Nitrogen || 2.7 × 10<sup>−10</sup> m || 3.64 × 10<sup>−10</sup> m
|-
| Chlorine || 4 × 10<sup>−10</sup> m || 3.20 × 10<sup>−10</sup> m
|}

{| class="wikitable"
|+ Atomic masses in kilograms
|-
! Molecule !! Perrin's measurements<ref name="Perrin 1909 p. 50"/> !! Modern measurements
|-
| Hydrogen || 1.43 × 10<sup>−27</sup> kg || 1.66 × 10<sup>−27</sup> kg
|-
| Oxygen || 22.7 × 10<sup>−27</sup> kg || 22.8 × 10<sup>−27</sup> kg
|}