Divalent and monovalent ions are often non-covalently bonded in biological molecules, they are primary building blocks of the machinery of biology. Iodine, the halogon in period 5, is covalently bonded in thyroxide. What are other examples of covalently bonded monovalent ions, alkali metals and halogens? Are there molecules that covalently bond Flourine, Chlorine, Sodium and Potassium?

  • $\begingroup$ Sodium and potassium are not going to be covalently bound in biological molecules. For fluorine: tcichemicals.com/en/ap/support-download/chemistry-clip/…, an example for chlorine: en.wikipedia.org/wiki/Epibatidine $\endgroup$
    – Ashafix
    Mar 21 '20 at 20:39
  • $\begingroup$ Thanks, very good answer. The Wiki page on Epibatidine mentions an "extremely high affinity". Gilbert Ling did some work between 1950 and to his death last year, and mentions Robert W. Taft, that may relate to why Epibatidine has "extremely high affinity". It seems that halogens like chlorine polarize the molecule. I'm assuming thyroxine has similar properties since iodine is also a halogen, also, the large effort required by organisms to synthesize thyroxine suggests it should pay off for some reason, so I'm looking a bit for information about that. $\endgroup$
    – Winstan
    Mar 22 '20 at 11:45
  • $\begingroup$ Try searching for "bioinorganic chemistry". $\endgroup$
    – David
    Mar 31 '20 at 22:04
  • $\begingroup$ A "covalent bond" affords close-to or full homopolarity of both bonding partners. Metals are genuinely low in electronegativity as in contrast to organic bonding partners like C,O,N, ... Thus there never can be colvalent bonds between such metal (cations) and organic moieties. $\endgroup$ Apr 1 '20 at 11:40

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