Welcome to science s.o.s. This time we are going to study the oxidation states.
What we have here is a small fraction of the periodic table. They are the representative elements.
But it is a small part. It goes from period 1, 2, 3 to 4, and from groups IA to group VIIIA
And these numbers that you see here, are the most common oxidation states for each of these groups.
What is the oxidation state?
It is the charge that an atom will acquire to obtain the electronic configuration of a noble gas.
For example, here we have lithium. If lithium loses an electron will have the electronic configuration of helium.
Because lithium has 3 electrons and helium has 2 electrons.
Each atom that acquires the electronic configuration of a noble gas will lower its energy level,
and will achieve stability,
you understand?
Here we have the sodium atom. Check your periodic table.
Perfect, there's the sodium.
How many valence electrons does it have?
it has 1 valence electrons
And here is the chlorine.
. How many valence electrons do you have?
Very good.
If it is in group 7, it has 7 valence electrons.
Here are the valence electrons.
We already saw that in atomic structure and the unit that corresponds to Lens and Lewis structure.
So you check it out.
Well, since chlorine is more electronegative than sodium,
The chlorine will remove an electron sodium.
Therefore, this electron is going to be erased and we are going to put it here
Since sodium lost an electron is going to be positively charged +1, it lost one electron.
As the chlorine gains an electron is going to be negatively charged.
We draw it in parentheses and the negative charge outside.
See, that's typical of an ionic bond. We can transform it into an empirical formula,
as seen in "ionic bond" in the previous video.
and this is it…
What is the oxidation state of sodium? +1.
What is the oxidation state of chlorine? -1.
Everything fits perfect.
What happens in covalent compounds?
Can we determine the oxidation state?
Of course we can do it.
Although in the covalent molecules there is no transfer of electrons,
in any case we can calculate the state of oxidation.
How is it done? In the following way:
The first thing to think is that here there is an ionic bond, you have to get that idea to be able to determine it.
So, if we had an ionic bond here, how many electrons would oxygen take away from carbon?
Oxygen would take away just the two they are sharing.
Therefore the oxygen oxidation state will be -2.
The most common oxidation state for group VI
And the most common oxidation state for oxygen
And this oxygen how much it would take away from carbon
I would take two
Therefore, its oxidation state will be -2.
What happens to carbon?
Carbon, with that oxygen, would lose 2, and with that other oxygen it would lose 2 more.
In total + 4.
And that is the oxidation state for carbon. See?
It has a variable oxidation state.
Recién les dije que el estado de oxidación más común para el oxígeno es -2,
except for peroxides. In peroxides the oxidation state of oxygen is -1.
Here we have a peroxide. It is hydrogen peroxide or hydrogen peroxide.
Here we have a peroxide. It is hydrogen peroxide or hydrogen peroxide.
Let's see, if this were an ionic bond, how many electrons would it remove?
None, and why none
Because they have no difference in electronegativity between atoms.
Hence, between them, the oxidation state will be zero.
But what happens here?
Which is more electronegative?
The oxygen is here and the hydrogen is here.
Therefore, if it were an ionic bond, oxygen could take away an electron,
but it is not, do not forget that.
Well, then the oxygen would be -1, because it takes one electron,
and the oxygen with that other hydrogen is -1, too.
Then, the oxygen oxidation state in the peroxides is always -1
How can we recognize a peroxide?
Because they are joined oxigen atoms.
Always in a peroxide we will have two oxygens,
and those two oxygens will be linked together.
Did you understand? very good perfect.
Let's keep going.
What happens here? We have a molecule a little bigger.
Can we calculate the oxidation state that way?
Of course we can.
Between sulfur and oxygen, which is more electronegative?
Of course oxygen.
So how many electrons would the oxygen remove from the sulfur if it were an ionic bond?
Very good, it'd take those two, then the oxygen is -2.
Of course it is -2, since this is not a peroxide.
Peroxides are those in which the oxygens are bound and the oxygen is -1.
Since oxygens are not bound here, the oxidation state is -2
Let's check. In this case
the oxygen with the sulfur are sharing one electron, at least one electron of the sulfur.
Then, the oxygen oxidation state there would be -1.
But in front of this hydrogen that is here, how much would it be?
-1 as well. In total it would be -2.
And this oxygen -1 with sulfur, -1 with hydrogen, in total -2.
And this oxygen from here, two electrons, if it were ionic would remove those two electrons,
What is the oxydation state?
-2
What about sulfur?
Let's see. The sulfur with that oxygen would lose 2 if it were an ionic bond.
So it would be +2.
With that other oxygen would also lose two, +2,
and with that oxygen there, one, +1,
and with the oxygen that is located here +1 too, in total it is +6,
oxidation state of sulfur.
To calculate the oxidation states, you can also use the rules of the oxidation states
that were developed from what I am telling you.
If you like to use the rules, you can do it. What do the rules say
The oxidation state of hydrogen is always -1 unless it is bound to a metal.
The oxygen oxidation state is always -2, except for the peroxides.
The oxidation state of fluor is always -1.
Then, with those rules and others, you can calculate states of oxidation.
Let's take the rules, of course, that's what we are here for.
Let's make sure they're fine. Let's make CO2, the molecule that's here.
CO2 would have this formula.
The oxidation state of the carbon we have here can be very variable ...
+4 ... -4, it can even be up to zero. We do not know what their oxidation state will be.
But we do know the oxidation state of oxygen.
How much is the oxidation state of oxygen?
-2, very well -2, because it is not a peroxide.
-2 x 2 because they are 2 oxygens, = 0
Now, all that remains is to determine and clear the X.
And the X will be +4, see? Oxidation state +4
slipped just with the molecule.
What do you think?
Do you want to make another example? Sulfuric acid, let's make sulfuric acid then.
Sulfuric acid has this formula: H2SO4.
Then … oxidation state of hydrogen …
Hydrogen is always +1 unless it is bound to a metal.
And here there is no metal, so it is +1 x 2.
Plus the sulfur, the sulfur is down here,
it has a state of variable oxidation,
so it's going to be an X.
Plus the oxygen, it's always -2,
except in peroxides and this, of course, is not peroxide.
Therefore, its oxidation state will be -2 x
how much oxygen is there? 4.
Okay, clear the incognita ... equal to zero.
Why is it equal to zero?
Because this is a neutral molecule, see?
? It has no charge, equal to zero.
We clear X, how much does the X give us? 6
OH! 6 here, 6 there,
perfect.
It is then checked how the oxidation states can be determined.
What did you think?
Easy, right? Fast and even entertaining.
See you in another chapter
of the fascinating world of chemistry,
here in Science SOS.
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