BASIC OXIDES: FORMATION, NOMENCLATURE, PROPERTIES - CHEMISTRY - 2025

The basic oxides are those formed by the union of a metal cation with a dianion of oxygen (O ^2-); they usually react with water to form bases, or with acids to form salts. Due to its strong electronegativity, oxygen can form stable chemical bonds with almost all elements, resulting in different types of compounds.

One of the most common compounds that an oxygen dianion can form is oxide. Oxides are chemical compounds that contain at least one oxygen atom along with another element in their formula; They can be generated with metals or non-metals and in the three states of aggregation of matter (solid, liquid and gaseous).

For this reason, they have a large number of intrinsic properties that can vary, even between two oxides formed with the same metal and oxygen (such as iron (II) and iron (III) oxide, or ferrous and ferric, respectively). When an oxygen joins a metal to form a metal oxide, a basic oxide is said to have formed.

This is because they form a base by dissolving in water or they react as bases in certain processes. An example of this is when compounds such as CaO and Na ₂ O react with water and result in the hydroxides Ca (OH) ₂ and 2NaOH, respectively.

Basic oxides are normally ionic in character, becoming more covalent while talking about elements to the right of the periodic table. There are also acidic oxides (formed from non-metals) and amphoteric oxides (formed from amphoteric elements).

Training

The alkali and alkaline earth metals form three different types of binary compounds from oxygen. Apart from oxides, peroxides (which contain peroxide ions, O ₂ ^2-) and superoxides (which contain superoxide O ₂ ^- ions) can also occur.

All oxides that are formed from alkali metals can be prepared by heating the corresponding nitrate of the metal with its elemental metal, such as what is shown below, where the letter M represents a metal:

2MNO ₃ + 10M + Heat → 6M ₂ O + N ₂

On the other hand, to prepare the basic oxides from the alkaline earth metals, their corresponding carbonates are heated, as in the following reaction:

OLS ₃ + Heat → MO + CO ₂

The formation of basic oxides can also occur due to treatment with oxygen, as in the case of sulfides:

2MS + 3O ₂ + Heat → 2MO + 2SO ₂

Finally, it can occur by oxidation of some metals with nitric acid, as occurs in the following reactions:

2Cu + 8HNO ₃ + Heat → 2CuO + 8NO ₂ + 4H ₂ O + O ₂

Sn + 4HNO ₃ + Heat → SnO ₂ + 4NO ₂ + 2H ₂ O

Nomenclature

The nomenclature of basic oxides varies according to their stoichiometry and according to the possible oxidation numbers that the metallic element involved has.

It is possible to use the general formula here, which is metal + oxygen, but there is also a stoichiometric nomenclature (or old Stock nomenclature) in which compounds are named by placing the word "oxide", followed by the name of the metal and its oxidation state in Roman numerals.

When it comes to systematic nomenclature with prefixes, the general rules are used with the word "oxide", but the prefixes are added to each element with the number of atoms in the formula, as in the case of "di-iron trioxide".

In traditional nomenclature, the suffixes «–oso» and «–ico» are used to identify the accompanying metals of lower or higher valence in an oxide, in addition to the fact that basic oxides are known as «basic anhydrides» due to their ability to form basic hydroxides when water is added to them.

In addition, this nomenclature uses the rules, so that when a metal has oxidation states up to +3 it is named with the rules of oxides, and when it has oxidation states greater than or equal to +4, it is named with the rules of anhydrides.

Summary rules for naming basic oxides

The oxidation states (or valence) of each element should always be observed. These rules are summarized below:

1- When the element has a single oxidation number, as for example in the case of aluminum (Al ₂ O ₃), the oxide is named:

Traditional nomenclature

Aluminum oxide.

Systematics with prefixes

According to the amount of atoms that each element has; that is, dialuminum trioxide.

Systematics with Roman numerals

Aluminum oxide, where the oxidation state is not written because it has only one.

2- When the element has two oxidation numbers, for example in the case of lead (+2 and +4, which give the oxides PbO and PbO ₂, respectively), it is named:

Traditional nomenclature

Suffixes "bear" and "ico" for minor and major, respectively. For example: plumb oxide for PbO and lead oxide for PbO ₂.

Systematic nomenclature with prefixes

Lead oxide and lead dioxide.

Systematic nomenclature with Roman numerals

Lead (II) oxide and lead (IV) oxide.

3- When the element has more than two (up to four) oxidation numbers, it is named:

Traditional nomenclature

When the element has three valences, the prefix «hypo-» and the suffix «–oso» are added to the smallest valence, as for example in hypophosphorous; the suffix «–oso» is added to the intermediate valence, as in phosphorous oxide; and finally, to the greater valence "–ico" is added, as in phosphoric oxide.

When the element has four valencies, as in the case of chlorine, the previous procedure is applied for the lowest and two following ones, but to the oxide with the highest oxidation number the prefix "per-" and the suffix "–ico" are added.. This results in (for example) a perchloric oxide for the +7 oxidation state of this element.

For systems with a prefix or Roman numerals, the rules that were applied for three oxidation numbers are repeated, remaining the same.

Properties

- They are found in nature as crystalline solids.

- Basic oxides tend to adopt polymeric structures, unlike other oxides that form molecules.

- Due to the considerable strength of the MO bonds and the polymeric structure of these compounds, the basic oxides are usually insoluble, but they can be attacked by acids and bases.

- Many of the basic oxides are considered non-stoichiometric compounds.

- The bonds of these compounds cease to be ionic and become covalent the further one advances per period in the periodic table.

- The acid characteristic of an oxide increases as it descends through a group in the periodic table.

- It also increases the acidity of an oxide in higher oxidation numbers.

- Basic oxides can be reduced with various reagents, but others can even be reduced with simple heating (thermal decomposition) or by an electrolysis reaction.

- Most of the really basic (not amphoteric) oxides are located on the left side of the periodic table.

- Most of the Earth's crust is made up of solid metal-type oxides.

- Oxidation is one of the paths that leads to corrosion of a metallic material.

Examples

Iron oxide

It is found in iron ores in the form of minerals, such as hematite and magnetite.

Additionally, iron oxide makes up the famous red "rust" made up of corroded metal masses that have been exposed to oxygen and moisture.

Sodium oxide

It is a compound used in the manufacture of ceramics and glasses, in addition to being a precursor in the manufacture of sodium hydroxide (caustic soda, a powerful solvent and cleaning product).

Magnesium oxide

A hygroscopic solid mineral, this compound high in thermal conductivity and low in electrical conductivity has multiple uses in construction (such as fire-resistant walls), and in the remediation of contaminated water and land.

Copper oxide

There are two variants of copper oxide. Cupric oxide is a black solid that is obtained from mining and that can be used as a pigment, or for the final disposal of hazardous materials.

On the other hand, cuprous oxide is a red semiconductor solid that is added to pigments, fungicides and marine paints to avoid accumulation of residues on ship hulls.

References

1. Britannica, E. (nd). Oxide. Retrieved from britannica.com
2. Wikipedia. (sf). Oxide. Retrieved from en.wikipedia.org
3. Chang, R. (2007). Mexico: McGraw-Hill.
4. LibreTexts. (sf). Oxides. Retrieved from chem.libretexts.org
5. Schools, NP (sf). Naming Oxides and Peroxides. Retrieved from newton.k12.ma.us