Editing Molecule (section)

== Molecular size ==

Most molecules are far too small to be seen with the naked eye, although molecules of many [[polymer]]s can reach [[macroscopic]] sizes, including [[biopolymer]]s such as [[DNA]]. Molecules commonly used as building blocks for organic synthesis have a dimension of a few [[angstrom]]s (Å) to several dozen Å, or around one billionth of a meter. Single molecules cannot usually be observed by [[light]] (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an [[atomic force microscope]]. Some of the largest molecules are [[macromolecule]]s or [[supermolecule]]s.

The smallest molecule is the [[diatomic]] hydrogen (H<sub>2</sub>), with a bond length of 0.74 Å.<ref>{{cite book| author= Roger L. DeKock| author2= Harry B. Gray| author3= Harry B. Gray| title= Chemical structure and bonding| url= https://books.google.com/books?id=q77rPHP5fWMC&pg=PA199| date= 1989| publisher= University Science Books| isbn= 978-0-935702-61-3| page= 199| access-date= 27 October 2020| archive-date= 31 March 2021| archive-url= https://web.archive.org/web/20210331062042/https://books.google.com/books?id=q77rPHP5fWMC&pg=PA199| url-status= live}}</ref>

Effective molecular radius is the size a molecule displays in solution.<ref>
{{cite journal
 |author=Chang RL |author2=Deen WM |author3=Robertson CR |author4=Brenner BM
 |title=Permselectivity of the glomerular capillary wall: III. Restricted transport of polyanions
 |journal=Kidney Int.
 |volume=8
 |issue=4
 |pages=212–218
 |year=1975
 |pmid=1202253
 |doi=10.1038/ki.1975.104
 |doi-access=free
}}</ref><ref>
{{cite journal
 |author=Chang RL  |author2=Ueki IF |author3=Troy JL |author4=Deen WM |author5=Robertson CR |author6=Brenner BM
 |title=Permselectivity of the glomerular capillary wall to macromolecules. II. Experimental studies in rats using neutral dextran
 |journal=Biophys. J.
 |volume=15
 |issue=9
 |pages=887–906
 |year=1975
 |pmid=1182263
 |doi=10.1016/S0006-3495(75)85863-2
 |pmc=1334749
 |bibcode= 1975BpJ....15..887C
}}</ref>
The [[table of permselectivity for different substances]] contains examples.