Silicates and Silicones: Structure From One Building Block

September 15, 2026

| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Main Group Silicates and Silicones: Structure From One Building Block Every silicate is built from the same tetrahedron. What varies is how many corners are shared, and that single number determines the structure. BSc & MSc · Inorganic Chemistry · Concept The short answer: A silicate tetrahedron shares between zero and four of its corner oxygens with neighbours. Sharing none gives discrete anions, two gives chains or rings, three gives sheets, and four gives a three-dimensional network. Silicones are synthetic polymers with a silicon–oxygen backbone and organic side groups. The building block Every silicate contains silicon at…

Substitution in Octahedral Complexes: Dissociative or Associative

September 15, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Mechanism Substitution in Octahedral Complexes: Dissociative or Associative Square planar substitution is associative; octahedral substitution is usually dissociative. The reason is simply how crowded the metal already is. BSc & MSc · Inorganic Chemistry · Concept The short answer: An octahedral complex is sterically crowded, so an incoming ligand cannot easily approach. Substitution therefore usually proceeds by a ligand leaving first, giving a five-coordinate intermediate. The evidence is that rates depend strongly on the leaving group and only weakly on the entering one. The two limiting mechanisms Dissociative Associative First step A ligand leaves, giving five-coordinate A…

Catalytic Cycles: Hydroformylation and the Wacker Process

September 14, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Catalysis Catalytic Cycles: Hydroformylation and the Wacker Process Industrial catalysis assembled from four elementary steps that repeat in different orders. Learn the steps and any cycle becomes readable. BSc & MSc · Inorganic Chemistry · Concept The short answer: Homogeneous catalytic cycles are built from a small set of elementary organometallic steps: oxidative addition, migratory insertion, reductive elimination and ligand substitution. Hydroformylation and the Wacker process are the two standard examples, and each is examined by asking which step does what. The elementary steps Step What changes Oxidation state Electron count Oxidative addition A bond adds across…

Crystal Defects and Non-Stoichiometry

September 13, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Solid State Crystal Defects and Non-Stoichiometry A perfect crystal would have zero entropy of disorder, which thermodynamics forbids above absolute zero. Defects are not flaws but a requirement. BSc & MSc · Inorganic Chemistry · Concept The short answer: Point defects exist in every real crystal because they increase entropy enough to lower the free energy despite costing enthalpy. Schottky defects remove ion pairs and reduce density; Frenkel defects relocate an ion and leave density unchanged. Non-stoichiometric compounds arise when defects are accompanied by a change in oxidation state. Why defects must exist Defects are thermodynamically required,…

Orgel and Tanabe–Sugano Diagrams: Interpreting d–d Spectra

September 13, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Spectra Orgel and Tanabe–Sugano Diagrams: Interpreting d–d Spectra Two diagrams for the same purpose, differing in whether they can handle a spin state change. BSc & MSc · Inorganic Chemistry · Concept The short answer: Both plot the energies of electronic terms against ligand field strength. Orgel diagrams cover weak-field high-spin complexes only. Tanabe–Sugano diagrams cover the whole range including the high-spin to low-spin crossover, and take the ground state as the horizontal axis so transition energies are read directly. What the diagrams show A free ion’s electronic states are described by term symbols. Placing that ion…

Noble Gas Compounds: Why Xenon Reacts and Helium Does Not

September 12, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Main Group Noble Gas Compounds: Why Xenon Reacts and Helium Does Not The elements once believed inert form a well-defined set of compounds, and which ones form is entirely predictable from ionisation energy. BSc & MSc · Inorganic Chemistry · Concept The short answer: Xenon has a low enough ionisation energy to be oxidised by fluorine and oxygen. Its fluorides have structures predicted correctly by VSEPR once the lone pairs are counted, and the fluorides hydrolyse to oxides and oxofluorides. Helium and neon do not react, because their ionisation energies are far too high. Why xenon and…

The Jahn–Teller Effect: Why Some Complexes Distort

September 11, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Structure The Jahn–Teller Effect: Why Some Complexes Distort A degenerate electronic state is unstable against distortion. Knowing which configurations are degenerate tells you immediately which complexes distort and how strongly. BSc & MSc · Inorganic Chemistry · Concept The short answer: A non-linear molecule in a degenerate electronic state will distort to remove that degeneracy, because doing so lowers the energy. In octahedral complexes the effect is strong for unevenly occupied eg orbitals and weak for uneven t2g occupation, because eg orbitals point directly at ligands. The statement Any non-linear molecule in a degenerate electronic state is…

Latimer and Frost Diagrams: Reading Redox Chemistry From a Picture

September 10, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Redox Latimer and Frost Diagrams: Reading Redox Chemistry From a Picture Two ways of displaying the same data, each answering a different question — one about individual couples, one about which species survive. BSc & MSc · Inorganic Chemistry · Method The short answer: A Latimer diagram lists reduction potentials between adjacent oxidation states. A Frost diagram plots nE° against oxidation state, so stability becomes visual: the lowest point is the most stable species, and any species lying above the line joining its neighbours will disproportionate. Latimer diagrams A Latimer diagram writes the oxidation states of an…

Metal Carbonyls: Synergic Bonding and What the Spectrum Reveals

September 9, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Organometallics Metal Carbonyls: Synergic Bonding and What the Spectrum Reveals The infrared stretching frequency of bound carbon monoxide is a direct readout of electron density at the metal, which makes it one of the most informative single measurements in the subject. BSc & MSc · Inorganic Chemistry · Concept The short answer: Carbon monoxide donates a lone pair to the metal and simultaneously accepts electron density from filled metal d orbitals into its own antibonding orbital. That back-donation weakens the C–O bond, lowering its stretching frequency — so the observed frequency measures how much back-donation is occurring….

The HSAB Principle: Predicting Which Combinations Are Stable

September 8, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Acids and Bases The HSAB Principle: Predicting Which Combinations Are Stable A qualitative rule that predicts a surprising amount — which minerals occur together, which ligands bind which metals, and which reactions go. BSc & MSc · Inorganic Chemistry · Concept The short answer: Hard species are small, highly charged and not easily polarised; soft species are large, less charged and readily polarised. Hard acids prefer hard bases and soft acids prefer soft bases. The rule is qualitative but predicts stability, solubility and reaction direction remarkably well. What hard and soft mean Property Hard Soft Size Small…

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