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What are they? |
How are they named? | If we
know the formula | If we know the name |
Peroxides |
Examples | Exercises
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What are they? |
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They are compounds formed
by a metal and oxygen, in which
the oxygen has an oxidation number –2.
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How are they named?
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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.
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If we know the formula |
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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.
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If we know the name |
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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.
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Peroxides |
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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 |
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Examples
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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 |
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Exercises
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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.
       
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