Let's take a quick look at the abstract world of atomic structure
The protons are in the middle the electrons go around the outside
the electrons are in energy levels there is two electrons
in the first energy level, eight electrons in the second energy level
and eight electrons in the third energy level
The octet rule tells is that the energy levels have to be full
by way of review, let's look at these two examples We have hydrogen
this is right off the periodic table hydrogen has a proton and an electron
violating the octet rule
it is the duet rule for hydrogen in the case of hydrogen
and then oxygen has six electrons in the outer energy level
again violating the octet rule a common structure
perhaps the most common structure in the universe ... is this one
which is H2O .... which is water The oxygen has a covalent bond
with two hydrogen atoms giving the hydrogen the two electrons it needs
and the oxygen the eight electrons it needs water---both the oxygen and the hydrogen
meet the octet rule .. the oxygen has eight and the hydrogens each have two
a familiar reaction of water
is that it dissociates into the hydrogen ion and the hydroxyl ion
if we look at the hydrogen ion, we see that it is a proton
it is a proton with no electron ..and...and it has a positive charge
and you look at it and you might say
"well it is unstable because it has a positive charge"
but that is not the case at all it is stable because it has a positive charge
and then if we look at the hydroxyl ion we see that it has eight electrons
but it has to have an extra electron giving it a negative charge
so similarly, you might look at the hydroxyl ion and say that it is unstable
because it has a negative charge, but it is the negative charge that makes it
meet the octet rule and it is the negative charge that makes it stable.
This is, of course, the hydrogen is ,of course, acid
and the hydroxyl is, of course basic, and, if either of these is in high concentration
they can be reactive, but as an individual particle they are not reactive at all
Let's assume that water will dissociate into a hydrogen atom and a hydroxyl free radical
(water does not do this)
okay, now if we look a this hydrogen atom we see that ...
this is a hydrogen proton and an electron it is electrically neutral
This particle may the most reactive particle in all of chemistry.
it violates ... it violates the duet rule the hydrogen needs two electrons
and it only has one and the result of this is that the
hydrogen free radical has a half life of a billionth of a second
when it appears in cells, which it does sometimes, the hydrogen free radical
it does not go looking for something to react with
It reacts with the first thing it comes to
and the first thing it comes to may very well be an aliphatic hydrogen
like the tail of a fatty acid; like a lipid
The way this works is that the hydrogen free radical finds a hydrogen and pulls it off
as another free radical and then the two free radicals combine to form hydrogen gas
This is a typical theme in free radical chemistry
two free radicals will typically neutralize each other.
And then the hydroxyl free radical ...notice the Lewis structure
We now have seven...is missing an electron they hydroxyl free radical
is somewhat less reactive, quite a bit more common in cellular biology
the reaction is the same; it does not choose something to react with
it reacts with the first thing it comes to
the chemistry is complex, but again, it is a high likelihood that it will react with
another hydrogen off of an aliphatic carbon compound and it will
pull this guy right out of here.. as a free radical, the two free radicals
...now, in this case it is the hydrogen free radical and the hydroxyl free radical
will combine to form H2O, will go right back to water.
and in both of these cases, it leaves behind a free radical...it leaves a scar on the
on the material that it attacked this is like the empty chair in the stadium
part of intuitive understanding of free radicals is that they are not very common
two free radicals will frequently neutralize each other, but free radicals are not very common
and the likelihood of two of them coming together is not high
when I was a chemistry student, I was not a very smart kid
the teacher would say "free radicals are unpaired electrons"
.........and I would go "free radicals are unpaired electrons, okay"
it is easier for me to see it as free radicals are violations of the octet rule
and that's it