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The mystery of oxides: Why are they so ubiquitous on Earth?
Oxides are an extremely important and common class of compounds in Earth's chemistry. They contain at least one oxygen atom and other elements and are among the most common compounds in nature. According to the chemical definition, oxides are chemical compounds containing oxygen, with the divalent anion of oxygen (O²⁻) forming the basis of such compounds.
In the Earth's crust, oxides make up the vast majority of its composition, and even many materials that are considered pure elements form oxides, such as the Al2O2 protective layer formed by aluminum foil in the air.
Oxides have a great diversity in chemistry and structure, ranging from binary oxides (containing only oxygen and another element) to more complex ternary or quaternary oxides. This diversity makes oxides play key roles both in nature and in industrial applications. Taking carbon dioxide and carbon monoxide as examples, the former is produced when carbon is completely oxidized in an aerobic environment, while the latter is produced in the absence of oxygen.
Formation of oxides
Oxides are associated with almost all elements, except for a few noble gases. Metal oxides are usually formed by thermal decomposition of other metal compounds, such as carbonates, hydroxides, etc. In the process of making calcium oxide, limestone (calcium carbonate) decomposes when heated and releases carbon dioxide.
Almost all elements react with oxygen to form oxides, for example zinc powder burns in air to form zinc oxide.
In the process of metal ore refining, metal sulfides are often required to be heated in air to generate oxides. For example, molybdenum disulfide (MoS₂) is converted into molybdenum trioxide after calcination, which is the precursor of almost all molybdenum compounds.
Metallic Oxides and Non-metallic Oxides
Metal oxides are an important class of oxides, usually produced by thermal decomposition of other compounds. Non-metallic oxides, such as carbon dioxide and carbon monoxide, are products of complete or partial oxidation of carbon or hydrocarbons. For example, when biogas (which is mainly methane) reacts with oxygen, it produces water and carbon dioxide.
In the industrial process of producing sulfuric acid, sulfur reacts directly with oxygen to form sulfur dioxide, which is then oxidized to form sulfur trioxide, and finally water is added to form sulfuric acid.
Structure and reaction
The structures of oxides range from molecular to polymeric and crystalline. Metal oxides usually exist as solid polymers at room temperature, while many non-metal oxides exist in gaseous or molecular form. Exceptions to this rule include gaseous oxides such as nitric oxide and nitrogen dioxide.
During the reaction of oxides, metal oxides can be converted into metals through reduction reactions. Most metal oxides decompose by heating, while others rely on chemical reducing agents such as carbon. During the iron refining process, iron oxide reacts with carbon to produce iron and carbon dioxide.
These reactions are not only crucial in industry, but also affect natural cycles, such as the iron cycle.
Nomenclature and chemical formula
The chemical formulas of oxides are usually predictable, especially in the case of the highest oxidation states. Although the formation of most metal oxides can be predicted based on their valence electrons, there are some exceptions. For example, the highest oxidation state of copper is copper(II) oxide, not copper(I) oxide.
Conclusion
In short, oxides are everywhere and affect every aspect of our lives, from the environment to industry. The forms and reactions of various oxides are the key to our understanding of nature and technological development. Have you ever wondered whether oxides will once again reveal more hidden secrets in future technological advances?
