What is the difference between an ionic bond and a covalent bond?

1 Answer
Jul 6, 2017

Answer:

From first principles, we regard the #"covalent bond"# as the result of the SHARING of electron density between atoms..........

Explanation:

.....And the #"ionic bond"# as the result of the transfer of electron density between atoms.....

Metals are electron rich materials; they are good reducing agents, and typically form #M^(n+)# ions........

#M rarrM^(+) + e^(-)#

On the other hand, non-metals are electron poor materials; they are good oxidizing agents, and typically form #X^(n-)# ions........ The position of metals, say the alkali metals, and non-metals on OPPOSITE ends of the Periodic Table, reflects this differential redox reactivity. Ions of the alkali metals, #Li^+#, #Na^+#, etc., and alkaline earths, #Mg^(2+)#, #Ba^(2+)#, can typically form. Meanwhile, non-metals, halogens, and chalcogens, can be readily reduced......

#X_2+2e^(-) rarr 2X^-# #X=F, Cl, Br.........#

#E_2 + 4e^(-) rarr 2E^(2-)# #E=O, S......#

I think you can see where this is going, because for every reduction, electron gain, there is an equal and corresponding electron loss, and thus metals can be typically oxidized to form discrete cations.....

#Li(s) + 1/2Cl_2(g) rarr LiCl(s)#

The resultant salt, here #"lithium chloride"#, is non-molecular, and consists of an infinite array of positively charged cations, #Li^+#, and negatively charged anions, #Cl^-#, held together by STRONG electrostatic forces. This ionic structure also rationalizes the typical properties of an ionic solid: high-melting; brittle; non-conductive in the solid state; soluble in highly polar solvents (and of course water is such a solvent).

So we have dealt in part with ionic bonding. What about the #"covalent bond"#? Covalent bonding is typically described as the SHARING of electron density.....but why should 2 electrons result in a bonding interaction.....?

The modern covalent bond is conceived to be a region of high electron density between 2 positively charged atomic nuclei, such that the nuclei are attracted to the electron cloud electrostatically.

galleryhip.com

If we mapped electron density, (which your text will do), there is a region of high electron density BETWEEN the nuclei, which effects the covalent bond. Because, the bond is between just 2 atoms, covalent bonding generally results in discrete particles, i.e. #"molecules"#.....

Anyway, none of this is ANY substitute for reading the chapter in your text. These are fairly simple ideas, and they reasonably easy to describe.