The net energy decrease when Na and Cl form NaCl

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EvaLi_3J
Posts: 53
Joined: Wed Oct 02, 2019 12:16 am

The net energy decrease when Na and Cl form NaCl

Postby EvaLi_3J » Sat Nov 02, 2019 1:55 pm

On the book P72 (2A.3),it is said that
"In summary, there is a net lowering of energy below that of the individual atoms,
provided the net attraction between ions is greater than the energy needed to make them.
The major contribution to the energy input is normally the ionization energy of the element
that forms the cation. Although some of this energy may be recovered from the
electron affinity of the nonmetal when the anion is formed, in some cases energy is also
needed to make the anion. That energy must also be recovered from the interactions
between ions. Typically, only metallic elements have ionization energies that are low enough
for the formation of ionic bonds to be energetically feasible ."

I looked at the example before it, but I still don't quite understand what this paragraph means. What exactly is the reason why that the energy of NaCl is lower than Na and Cl atoms?

AKhanna_3H
Posts: 104
Joined: Wed Sep 18, 2019 12:19 am

Re: The net energy decrease when Na and Cl form NaCl

Postby AKhanna_3H » Sat Nov 02, 2019 3:43 pm

Na and Cl independently are less stable than when they are bonded because they have incomplete octets as ions. They bond together to achieve a lower energy state and are more stable.

KDang_1D
Posts: 127
Joined: Fri Aug 30, 2019 12:15 am
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Re: The net energy decrease when Na and Cl form NaCl

Postby KDang_1D » Sat Nov 02, 2019 4:35 pm

Hmm, I think this is a little more detailed than necessary. I believe it's explaining that all processes require energy, and the formation of ionic bonds is driven by the cation in the compound. More than the electron affinity of the anion, the ionization energy of the cation wanting to lose its extra valence electron typically drives the interaction. In conclusion, ionic bonds only form between metals and nonmetals because the ionization energy of nonmetals is not low enough for it to be favorable for this positive ionization to occur.


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