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Oxidation States of Transition Metals

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Transition metals can be a little confusing, but this lesson will simplify things by explaining why transition metals can have more than one oxidation state. It will also touch on other topics such as half equations and colored solutions.

What is a Transition Metal?

The periodic table is filled with fascinating elements. For example, did you know:

• Nearly all of the earth's core is made of iron.

• Vanadium is named after a Scandinavian goddess.

• Although it's highly toxic, people used to use mercury as a cure-all for a whole list of aliments.

So, other than being neat, what do iron, vanadium, and mercury have in common? Well… I'm so glad you asked. These are three of the transition metals, found in groups 3 through 12 on the periodic table. These metals have varying oxidation states which can make them a little confusing. Wait, oxidation states? Yep, let's check it out!

The yellow colored elements are the transition metals and are groups 3 through 12
predate

Oxidation State

In order to understand transition metals, we need to delve into oxidation states, (which are sometimes referred to as oxidation numbers). These are numbers that are assigned to each element and show how many electrons the element would lose or gain if it were to bond to other atoms.

For example, iron can have an oxidation state of +3. This means that iron has lost three electrons. Oxygen (which isn't a transition metal) has an oxidation state of -2. This means it gained 2 electrons. You see, some atoms like to give away their electrons and some like to take them.

Before we move on, it's worth going over two more terms: oxidation and reduction.

  • Oxidation means something lost electrons. If the oxidation state (number) increases, there has been an oxidation. Or, the atom was a giver.
  • Reduction means something gained electrons. If the oxidation state (number) decreases, the substances have been reduced. Or, the atom was a taker.

Keeping these two things straight will make your life easier. Remember: LEO the lion goes GER. So… LEO stands for Loses Electrons Oxidation and GER stands for Gains Electrons Reduced.

Now, a lot of the elements on the periodic table are simple. For example, the group 1 elements, also called the Alkali Metals, have a +1 oxidation state. Or the group 2 elements, or Alkaline Earth Metals, have a +2 oxidation state. But, alas, our troublesome transition metals aren't so straightforward. So, while they are neat, they are a little complicated.

Why Multiple Oxidation States?

Electrons are oriented around the nucleus, or the center, of the atom. Some of these electrons are closer to the nucleus and some are further away. Generally, it is easier to take electrons that are further away from the nucleus.

Think back to those group 1 elements (Alkali Metals) we mentioned earlier. In these elements, the electron furthest away from the nucleus can be removed, but it would take too much energy to remove the electrons closer to the nucleus. This is why chemists can say with good certainty that those elements have a +1 oxidation state. It means that chances are, the Alkali Metals have lost one and only one electron.

However, with the transition metals, there are a bunch of electrons that take about the same amount of energy to remove. It's possible that one electron is removed, but it is also possible two, three, or four could be removed (depending on the transition metal). So, these transition metals can have numerous oxidation states.

For example, iron can be found in several oxidation states such as +2, +3, and +6. It's also worth noting that chemists have found a way to let you know the oxidation state of the element by placing a Roman numeral after its name. For example Iron (II) is iron with a +2 oxidation state. Iron (III) is iron with a +3 oxidation state and Iron (VI) is iron with a +6 oxidation state. Geez, not only do you have to do chemistry, you have to brush up on your Roman numerals!

Half Equations

Chemists can show the losing or gaining of electrons with half equations. Let's look at an example to get the general idea.

Look at the half equation for the oxidation of iron. Remember LEO GER? If iron is oxidized, it lost an electron and the oxidation state is changed. The oxidation state is represented by a superscript, and the electron is represented by an 'e.' You can see that iron (Fe) starts out with a +2 oxidation state, but it is oxidized so it loses an electron. The arrow shows that the reaction took place and iron is left with a +3 oxidation state and an electron (with a negative charge).

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