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

September 13, 2026

| 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…

Nuclear Chemistry: Decay Kinetics, Stability and Applications

September 8, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Nuclear Nuclear Chemistry: Decay Kinetics, Stability and Applications Radioactive decay is first-order kinetics applied to nuclei, so the mathematics is already familiar. What is new is what decides which nuclei decay at all. BSc & MSc · Inorganic Chemistry · Concept The short answer: All radioactive decay is first order, so half-life is independent of the amount present. Which mode a nucleus takes depends on its neutron-to-proton ratio relative to the band of stability: too many neutrons favours beta emission, too few favours positron emission or electron capture, and very heavy nuclei emit alpha particles. Decay kinetics…

Lanthanides: The Contraction and Why Separation Is So Hard

September 7, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · f Block Lanthanides: The Contraction and Why Separation Is So Hard One structural fact — poor shielding by f electrons — explains the contraction, the similarity of the elements, and the difficulty of separating them. BSc & MSc · Inorganic Chemistry · Concept The short answer: Across the lanthanide series the 4f electrons shield the nuclear charge poorly, so the effective nuclear charge rises steadily and the ionic radius falls. That contraction makes the elements chemically almost identical, which is why they occur together and separating them requires methods exploiting very small differences. What the contraction is…

Boranes and Wade’s Rules: Predicting Cluster Shapes

September 6, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Main Group Boranes and Wade’s Rules: Predicting Cluster Shapes Boron clusters look chaotic until you count skeletal electron pairs. Then each structure follows from a single number. BSc & MSc · Inorganic Chemistry · Method The short answer: Count the skeletal electron pairs. For n boron vertices, n+1 pairs gives a closo structure, n+2 gives nido, n+3 gives arachno. Each type is derived from the closo polyhedron by removing vertices, so the shapes are related rather than independent. Why boranes need special treatment Boron has three valence electrons but four valence orbitals, so it cannot form enough…

Stability Constants and the Chelate Effect

September 5, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Coordination Stability Constants and the Chelate Effect Why a ligand that bites twice binds far more tightly than two ligands that bite once — and why the answer is entropy, not bond strength. BSc & MSc · Inorganic Chemistry · Concept The short answer: Complex formation proceeds stepwise, each step with its own constant, and the overall constant is their product. Chelating ligands give far larger overall constants than comparable monodentate ligands. The dominant reason is entropic: one chelate molecule replaces several monodentate ones, increasing the number of free particles. Stepwise and overall constants Ligands add one…

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