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.
