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We all know that carbon mostly forms covalent bonds (almost always) and sodium mostly forms ionic bonds (almost always). But if $\ce{NaOH}$ reacts with ethyne, then $\ce{HC#CNa}$ and $\ce{H2O}$ are formed. Then what type of bond will $\ce{C-Na}$ be: mostly ionic or covalent?

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    $\begingroup$ en.wikipedia.org/wiki/Organosodium_chemistry $\endgroup$ – Nilay Ghosh May 18 '20 at 7:50
  • $\begingroup$ Well, I get the point that this bond is highly polar due to the high electronegativity difference between them . But if you were to classify it as either ionic or covalent, which one would you prefer to go for? $\endgroup$ – Habib May 18 '20 at 8:01
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    $\begingroup$ Generally, the difference between an ionic and a covalent bond is quite vague. Usually, it just comes down to an arbitrary difference in electronegativity on the Pauling scale of electronegativity. Most chemists agree that an electronegativity difference greater than 1.7 renders a bond ionic. Because the C-Na bond difference in electronegativity is 1.62, we would call it a polar covalent bond. Again, this definition is VERY arbitrary, and often times chemists will think of polar covalent bonds like the C-Na bond as ionic or ionic bonds as covalent (in some forms of organometallic chemistry). $\endgroup$ – Eli Jones May 18 '20 at 8:26
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    $\begingroup$ @EliJones It can be done better then that chemistry.stackexchange.com/questions/17064/… $\endgroup$ – Mithoron May 18 '20 at 12:24
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Electronegativity of Carbon is $2.55$ and that of Sodium is $0.93$ (from Wikipedia) so by the Haney-Smith equation (from J.D. Lee's Inorganic chemistry, third edition) $$\%\text{Ionic Character} = 16 |\Delta\chi| =3.5 (\Delta\chi)^2,$$ where $\Delta \chi$ is the difference in electronegativity of the two atoms. Carrying out the calculation gives us $$\% \textrm{Ionic Character} = 35.1054$$ So, it shows that the bond $\ce{C-Na}$ has a less ionic character.

In Organic Chemistry by Morrison and Boyd we find

The carbon-magnesium bond is covalent but highly polar, with carbon pulling the electrons from electropositive magnesium [...].
But, whatever the metal, it is less electronegative than carbon, and the carbon-metal bond - like the one in the Grignard reagent - is highly polar. Although, the organic group is not full-fledged carbanion [...] it nevertheless has considerable carbanion character.

Note: No bond is completely ionic or covalent, what matters is which character is dominant and hence the bond will behave like that.

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