Inorganic chemistry

Inorganic chemistry studies the structures, bonding, reactions, and properties of inorganic substances, including coordination complexes, metals, minerals, salts, and extended solids. Its scope overlaps organic chemistry when carbon-containing ligands or metal-carbon bonds are involved.

For example, changing a metal ion's ligands can alter its geometry, color, magnetic state, and reaction pathways. Studying that change requires both molecular electronic structure and evidence from measurements such as spectroscopy or diffraction.

Copper(II) hydroxide is $\mathrm{Cu}(\mathrm{OH}{)}_2$, a copper(II)-containing solid formed under suitable basic precipitation conditions. Its blue appearance is associated with the electronic environment of copper ions.

Its formation depends on solution equilibria and competing ligands. Adding hydroxide to a copper-containing solution does not guarantee the same product in every medium, because complexation changes the available species.

Magnesium hydroxide is $\mathrm{Mg}(\mathrm{OH}{)}_2$, a sparingly soluble hydroxide solid. Its dissolution equilibrium connects dissolved magnesium and hydroxide activities with a solubility product.

Acid consumes hydroxide and can drive further dissolution. This illustrates why an insoluble-looking solid can still have substantial acid-neutralizing capacity: removal of dissolved reaction products shifts the coupled equilibrium.

The oxidizing nitric-acid and hydrochloric-acid mixture historically called nitrohydrochloric acid. Reaction products and metal speciation depend on its composition and conditions.

A yellow phosphate-containing precipitate used under suitable acidic conditions in qualitative phosphate tests.

Calcium sulfate is $\mathrm{CaS}{\mathrm{O}}_4$, containing calcium and sulfate ions. Hydrated forms contain additional crystal water, so the hydrate state is part of a material's composition.

A calcium-sulfate solid can separate from phosphate-bearing liquor in historical phosphorus preparation. Interpreting that separation requires the relevant solubility and phase conditions, rather than treating all calcium salts as interchangeable.

An ionic potassium–iodide salt. Its preparation and purity tests distinguish iodide from iodate and free iodine.

The potassium salt of nitrate. Controlled heating can give potassium nitrite and oxygen.

A chemical compound containing a metal and oxygen; different metal oxidation states can give different oxides.

Indium oxide usually denotes indium(III) oxide, $\mathrm{I}{\mathrm{n}}_2{\mathrm{O}}_3$, a solid chemical compound of indium and oxygen. Formal oxidation states of $+3$ for indium and $-2$ for oxygen give charge balance: $2(3)+3(-2)=0$. The formula expresses the elemental ratio; it does not imply discrete molecules in the solid.^[ref]

Doping this oxide with tin produces the material family indium tin oxide, used for transparent conducting layers. Electrical and optical performance depend on charge-carrier density and preparation, so knowing the host compound's formula alone does not specify a film's conductivity.^[ref]

Indium tin oxide is a conducting oxide material based on indium oxide doped with tin. It is valued for combining substantial electrical conductivity with transmission of visible light, allowing a thin layer to function as an electrode through which light can pass. Its composition is not represented by one universal stoichiometric formula.^[ref]

The two properties probe different responses. Direct-current conduction measures mobile charge carriers, while optical transmission depends on frequency-dependent absorption and reflection as well as film thickness. Increasing carrier density can therefore change the optical response together with conductivity. Measurements of Hall effect and optical resonances help connect the electrical and optical descriptions of the same film.^[ref]

An iron hexacyanoferrate material, often hydrated and nonstoichiometric; $\mathrm{F}{\mathrm{e}}_4[\mathrm{Fe}(\mathrm{CN}{)}_6{]}_3$ is an idealized composition used to explain a historical cyanide recognition test.

Silver nitrate is the ionic salt $\mathrm{AgN}{\mathrm{O}}_3$, supplying silver cations and nitrate anions in aqueous chemical solution. Addition of a suitable halide can precipitate a silver halide.

For example, chloride gives silver chloride. The observation depends on competing ligands and solubility, so a precipitate test must be interpreted with the rest of the sample chemistry.

A family of calcium–silicon–oxygen chemical compounds. The metasilicate $\mathrm{CaSi}{\mathrm{O}}_3$ is a simple model for one reaction in slag formation.

A class of iron–oxygen chemical compounds, including oxides with different iron oxidation states.

Iron(III) oxide is ferric oxide, conventionally written $\mathrm{F}{\mathrm{e}}_2{\mathrm{O}}_3$. The formula assigns iron the formal oxidation state +3 when oxygen is treated as oxide.

Historical medicinal usage of peroxide of iron can refer to ferric oxide or hydrated ferric-oxide material. That name does not establish an oxygen-oxygen peroxide linkage, illustrating why historical material names require a composition convention.

Magnesium oxide is $\mathrm{MgO}$, the oxide historically called magnesia. In the ideal ionic description, magnesium is divalent and oxygen is present as oxide.

Reaction with an acid converts the oxide into a magnesium-containing salt and water. Its high-temperature stability also makes magnesium oxide useful as a refractory material, connecting strong solid-state bonding with resistance to heating.

A salt containing ammonium and nitrate. Its thermal decomposition has condition-dependent pathways; the familiar nitrous oxide pathway is not universal.

Potassium perchlorate is $\mathrm{KCl}{\mathrm{O}}_4$, containing potassium cations and perchlorate anions. Chlorine has formal oxidation state +7 in the perchlorate ion.

Potassium perchlorate can occur as an intermediate in uncatalysed potassium chlorate decomposition. The intermediate's formula and oxidation state distinguish a reaction pathway from the final net conversion to potassium chloride and oxygen.

Potassium chlorate is $\mathrm{KCl}{\mathrm{O}}_3$, containing potassium cations and chlorate anions. The final net thermal decomposition can be written $2KCl{\mathrm{O}}_3⟶2KCl+3{\mathrm{O}}_2$.

The balanced equation specifies the overall material inventory. It does not specify a unique sequence of intermediates: conditions and catalysts can change the route, including the role of potassium perchlorate.

The anion of hypochlorous acid. Its chemistry underlies many chlorine-based bleaching materials.

A calcium salt of hypochlorite. It must be distinguished from the variable commercial composition of bleaching powder.

Calcium oxide is $\mathrm{CaO}$, commonly called quicklime. It is produced by calcination of calcium carbonate, releasing carbon dioxide.

Reaction with water forms calcium hydroxide and releases heat. The distinction among carbonate, oxide, and hydroxide connects the lime cycle with both gas release and water uptake.

A historical material name used for quicklime or, in some contexts, hydrated lime; the intended composition must be specified.

The historical commercial material made by exposing calcium hydroxide to chlorine. Its useful oxidizing content is described by available chlorine; it should not be identified unconditionally with pure calcium hypochlorite.

The oxidizing capacity of a bleaching material expressed as the equivalent mass of chlorine.

Chemistry of finite bonded groups of atoms with molecular or metal-like skeletal bonding. Localized bond counts, skeletal-electron rules and delocalized shell models apply in different regimes.

An electronic model replacing discrete positive ionic cores by a smooth positive background. Approximately spherical clusters can be stabilized at closed angular-momentum shells.

A cluster whose nonhydrogen skeleton includes both carbon and aluminium. Exocyclic bonding must be distinguished from skeletal bonding when applying electron-counting rules.