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How do we create oxide names based on their molecular formulas?

Oxygen compounds with other elements are called oxides. The only exception is the oxygen‑fluorine compound, called oxygen fluoride. In all oxides, oxygen has a valency of two. On this basis, knowing the oxide formula, we can determine the valency of elements in oxides.

The names of oxides are double‑segmented. The first term is the name of the element in the genitive and the second – the word oxide e.g. sodium oxide. Many elements create several oxides in which their valency is different. An example is the compounds of lead with oxygen with the following molecular formulas: $\text{Pb}{\text{O}}_{\text{2}}$ and $\text{PbO}$.
In the first oxide, lead has a valency of four, in the second - two. Therefore, to uniquely determine the type of compound, e.g. oxide, its name often gives the valency of the element connected with oxygen. The compounds of the formulas discussed above $\text{Pb}{\text{O}}_{\text{2 }}$ and $\text{PbO}$ are respectively: lead(IV) oxide and lead(II) oxide. Oxygen valency is not determined in the names of oxides, since it is always two (II).

Exercise 1

Watch the presentation ‘Creating the name of a chemical compound based on its total formula’. Note your conclusions.

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Grafika slajdu. Na niebieskim tle napis Creation of a chemical compound name based on its total formula

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Grafika. Na białym tle duży niebieski napis en dwa o trzy, N2O3, dinitrogen trioxide

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Grafika. Na białym tle duże skrzyżowane niebieskie strzałki. En dwa łączy się z rzymską dwójką, o trzy łączy się z rzymską trójką.

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Grafika. Na białym tle duży niebieski napis en dwa o trzy, niżej napis dinitrogen trioxide.

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Conclusions about creating names of chemical compounds (Uzupełnij).

Conclusions about creating names of chemical compounds (Uzupełnij).

Conclusions about creating names of chemical compounds

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Nagranie dźwiękowe abstraktu

Nagranie dźwiękowe abstraktu

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Nagranie dźwiękowe abstraktu

By creating the names of metal oxides belonging to groups 1st and 2nd, their valency is not given, because these elements always have only one characteristic valency in chemical compounds: metals from 1st group - one, from 2nd group – two. A similar principle applies to aluminum: due to the fact that this element has a valency of three, it has been assumed not to give its valency in the name of the compounds.

How do we determine molecular formulas based on the name?

Based on the full name of the oxide, you can easily write its molecular formula. Remember that oxygen valency in these compounds is two. The valency of the second element must be known or it is given in the name. If the element belongs to the 1st group of the periodic table, its valency will be equal to one, if it is the element located in the 2nd group, it will have the valency equal to two.

Writting molecular formula of barium oxide

We determine the valency of particular elements that make up the oxide:

We write the molecular formula of barium oxide: BaO

Writting molecular formula of dinitrogen pentoxide

We determine the valency of particular elements that make up the oxide:

We are writting molecular formula of dinitrogen pentoxide: NIndeks dolny 2₂OIndeks dolny 5₅

How do we create structural formulas of covalent compounds based on the knowledge of the valency of elements?

Determining the structural formula of a compound molecule based on its molecular formula is not always possible. For example, without knowing about the existing connections between individual atoms, we will not draw a formula of a compound molecule consisting of three elements with a molecular formula ${\text{H}}_{\text{2}}\text{S}{\text{O}}_{\text{4}}$. In the case of two‑element compounds, it is possible if you know the valency of both elements. The easiest way to draw a formula of a molecule made of two atoms. An example is a molecule created by combining nitrogen and oxygen, the valency of which is two. It has the following structural formula:

$\text{N = O}$

Both atoms of elements have a valency equal to two and form two bonds each.

Summary

• Oxygen in oxides has valency equal to two. Based on this information and compound molecular formula, valency of the second element in the connections with oxygen can be determined.

• The names of oxides give the valency of the element which in chemical compounds may have different valency.

Key words

structural formula, valency

Glossary