Metal oxides

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What are they?  |  How are they named? If we know the formula  | If we know the name  |  Peroxides  |  Examples  |  Exercises 

What are they?

They are compounds formed by a metal and oxygen, in which the oxygen has an oxidation number –2.

How are they named?

For its nomenclature we use the:

Stock´s nomenclature: it is formed by two words. The first word is the name of the metal, followed immediately by the oxidation number between brackets and in Roman numbers. If the oxidation number of the metal is invariable, it is not indicated. The second word is the root of oxygen plus the suffix "–ide"

METAL(N) oxide

The IUPAC also accepts the stoichiometric nomenclature for these oxides, though it is better to use the Stock´s nomenclature when there are metallic atoms and the stoichiometric nomenclature when all the atoms are nonmetals.

If we know the formula

In the formula: oxygen has an oxidation number –2, and the oxidation number of the metal can be deduced by knowing that the compound is neutral. If it is always the same, we must know it and it is not necessary to deduce it.

How to determine the oxidation number of the metal?

1. Multiply the oxidation number of oxygen (–2) by its subscript. Change the sign of the result.
2. Divide this result by the subscript of the metal. This it is the value of the oxidation number of the metal, and of the Roman number that you must use.



If we know the name

In the name: Remember that you must know the symbols of the elements and the oxidation numbers that are invariable.

1. Write the symbol of the first element with the oxidation number; it is either between brackets or you have to know it.
2. Write the symbol of oxygen with an oxidation number –2.
3. Calculate the fewest atoms of each element that you need so that the compound be neutral.




There are oxides which have oxygens united by a simple bond (–O–O–), as the oxygenated water or hydrogen peroxide H2O2 (H–O–O–H). The ion dioxide(2–) or ion peroxide, O22–, forms peroxides with elements of the groups 1, 2, 11 and 12.

In these compounds oxygen has an oxidation number –1.

As nearly all the elements of the groups 1, 2, 11 and 12 have an invariable oxidation number , and we must know them, there is no confusion with the oxides of the oxide(2–) ion, O2–. For example:

Peroxide Stock´s nomenclature
Na2O2 Sodium peroxide
K2O2 Potassium peroxide
MgO2 Magnesium peroxide
CaO2 Calcium peroxide
Cu2O2 Copper(I) peroxide
ZnO2 Zinc peroxide





Stock´s nomenclature

Na2O Sodium oxide
MgO Magnesium oxide
CaO Calcium oxide
Li2O Lithium oxide
Ag2O Silver oxide
FeO Iron(II) oxide
Fe2O3 Iron(III) oxide
CrO3 Chromium(VI) oxide
TiO2 Titanium(IV) oxide
Cu2O Copper(I) oxide
CuO Copper(II) oxide
ZnO Zinc oxide



In Formulae you have an exercise to write the names of these substances and to check your results. You also have the answer to the exercise.

In Names you have an exercise to write the formulae for these substances and to check your results. You have to introduce the formulae without subscripts, for example for water = H2O. You also have the answer to the exercise.

Formulae 1 Names 1 Formulae 2 Names 2 Formulae 3 Names 3 Formulae 4 Names 4


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