Inorganic chemistry

Inorganic chemistry is the study of the synthesis and behavior of inorganic and organometallic compounds. This field focuses on chemical substances that are not based on carbon. This distinguishes it from organic chemistry, though the two fields overlap in organometallic chemistry. Inorganic compounds are essential to both the natural world and human industry. They appear in nature as minerals like pyrite or gypsum. They also function as vital biomolecules. For example, electrolytes like sodium chloride help biological systems, and ATP stores energy. Even the polyphosphate backbone of DNA is an inorganic structure.

Chemical bonding in inorganic compounds varies significantly. Some are ionic compounds, which consist of cations and anions joined by ionic bonding. An example is magnesium chloride, made of magnesium cations and chloride anions. Other compounds are highly covalent, such as sulfur dioxide. Many others feature polar covalent bonding, which is an intermediate state between ionic and covalent. These compounds often have high melting points. Some salts, like sodium chloride, are highly soluble in water. Additionally, acid-base chemistry can occur when a reactant contains hydrogen atoms. In this context, a Lewis acid is any species that can bind to electron pairs. A Lewis base is a molecule that tends to donate an electron pair.

Coordination chemistry is a major subdivision of this field. It involves coordination compounds where metals are bound to ligands. In classical versions, metals bind to lone pairs of electrons on atoms like water or ammonia. Modern coordination chemistry uses almost all organic and inorganic compounds as ligands. The metals involved are often from groups 3 through 13 or the lanthanides and actinides. These complexes show diverse structures, such as tetrahedral, square planar, or octahedral shapes. For example, cobalt complexes can be octahedral.

A famous example is the iron in hemoglobin, which is biologically essential.

Main group chemistry focuses on elements from groups I through VII and group 0. This excludes hydrogen but may include elements like scandium or zinc. These compounds have been known since the beginning of chemistry. For instance, early scientists studied elemental sulfur and white phosphorus. Lavoisier and Priestley performed experiments on oxygen, which helped define stoichiometric ratios in reactions.

Another major milestone occurred in the early 1900s. Carl Bosch and Fritz Haber developed a way to synthesize ammonia using iron catalysts. This process, known as the Haber process, had a massive impact on mankind. It demonstrated the power of inorganic chemical synthesis.

Organometallic chemistry specifically studies compounds containing metal-carbon bonds. This area is important because organic ligands are often sensitive to oxidation or hydrolysis. This requires specialized preparation methods compared to traditional complexes. Organometallic chemistry is highly relevant to industry because many ligands are petrochemicals.

This field also includes metal carbonyls and metal alkoxides. These compounds are vital for organic synthesis, where organometallic catalysts are frequently used as reagents.

Cluster chemistry involves groups of atoms bonded together, often in triangular sets. These clusters exist in pure inorganic systems, organometallic chemistry, and bioinorganic chemistry.

Large clusters act as an intermediate between a single molecule and a bulk solid. This interface is the basis for nanoscience and nanotechnology. One example is the study of quantum size effects in cadmium selenide clusters.

In biology, iron-sulfur clusters are central components of proteins used in human metabolism.

Inorganic chemistry is also highly practical for the global economy. Traditionally, a nation's productivity could be measured by its production of sulfuric acid. Man-made compounds like ammonium nitrate are essential for fertilizer. The Haber process produces the ammonia needed for this. Other large-scale materials include portland cement. Inorganic compounds also serve as catalysts, such as vanadium(V) oxide or titanium(III) chloride. Furthermore, solid state chemistry studies materials like silicon chips or superconductors.

Finally, many inorganic compounds are magnetic or colored, which helps scientists understand their structure through spectroscopy.