Video: Defining Delocalized Electrons

Which of the following is the best description of delocalized electrons in metallic bonding? [A] Core electrons that can move freely between metal ions [B] Valence electrons that can move freely between metal ions [C] Core and valence electrons that can move freely between metal ions [D] Valence electrons bound to metal ions [E] core electrons bound to metal ions

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Video Transcript

Which of the following is the best description of delocalized electrons in metallic bonding? A) Core electrons that can move freely between metal ions. B) Valence electrons that can move freely between metal ions. C) Core and valence electrons that can move freely between metal ions. D) Valence electrons bound to metal ions. Or E) core electrons bound to metal ions.

Let’s have a quick recap of metallic bonding. Lithium is a metal in group one of the periodic table. It has the symbol Li. It has two core electrons and one valence electron. Valence refers to the outer shell and core to anything below the outer shell. Lithium is said to have the electron configuration 2,1. Lithium metal is a lattice of lithium.

The lithium atoms give up their outer electron in the valence shell to form lithium plus ions. While the valence electron of each ion becomes delocalized and can hop freely from one ion to the next, forming part of the sea of delocalized electrons. So, while the valence electrons are free to move between ions, the core electrons are fixed in place. If we’d started with magnesium or aluminum, metals with more valence electrons, we would get roughly the same picture but with ions with a greater charge and more delocalized electrons.

Now that we’ve gone over the basics of metallic bonding, let’s evaluate the statements to see which one is the best description of delocalized electrons in metallic bonding.

Statement A says that core electrons can move freely between metal ions. This statement is false. We know that the core electrons are bound to the ion they started on. They are not delocalized. Therefore, this is not a correct answer.

Now on to option B. Statement B says that valence electrons can move freely between metal ions. This means they are delocalized. They are not fixed to any particular ion. Based on our experience with lithium, we know that this statement is true. Valence electrons become delocalized in metallic bonding. But before we decide that this is the best description, let’s have a look at the other options.

Option C says that both core and valence electrons are delocalized. However, we already know this to be false because core electrons are bound to the ion they started on. Therefore, this too is an incorrect answer.

What about option D? Statement D says that valence electrons are bound to the metal ions. This is false because the valence electrons become delocalized in metallic bonding. Therefore, this too is an incorrect answer. And we could move on to option E.

Option E says that core electrons are bound to metal ions. This statement is true. We know that when metal atoms bond together in metallic bonding, they hold onto their core electrons. This might be confusing at first. We have two true answers. However, if you look carefully, the question asks us for the best description of delocalized electrons. The question isn’t about the core electrons.

So, even though the statement is true, it is not relevant to the delocalized electrons and is, therefore, not the correct answer. Therefore, of the options given, the best description of delocalized electrons in metallic bonding is that they are valence electrons that can move freely between metal ions.

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