Electron Transfer: Inner Sphere versus Outer Sphere

September 5, 2026

| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Mechanism Electron Transfer: Inner Sphere versus Outer Sphere Two mechanisms distinguished by one question — does a ligand bridge the two metals during transfer, or not? BSc & MSc · Inorganic Chemistry · Concept The short answer: In outer sphere transfer the coordination shells stay intact and the electron tunnels between them. In inner sphere transfer a bridging ligand connects the two metals and the electron passes through it. The classic evidence is ligand transfer: if the bridging ligand ends up on the other metal, the mechanism was inner sphere. The two mechanisms Outer sphere Inner sphere…

Supramolecular Chemistry: Crown Ethers, Cryptands and Host–Guest Binding

September 4, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Entrance Exams Supramolecular Chemistry: Crown Ethers, Cryptands and Host–Guest Binding Chemistry beyond the covalent bond — where selectivity comes from the size of a hole and the number of contacts, not from making or breaking bonds. BSc & MSc · Inorganic Chemistry · Concept The short answer: Supramolecular chemistry studies assemblies held together by non-covalent forces. A crown ether binds an alkali metal ion whose radius matches its cavity, which is how selectivity is achieved without any covalent chemistry. Cryptands enclose the ion in three dimensions and bind far more strongly still. The extra stability of a…

Term Symbols and Russell–Saunders Coupling, Step by Step

September 4, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Spectra Term Symbols and Russell–Saunders Coupling, Step by Step A mechanical procedure that looks abstract. Follow the five steps in order and any ground-state term symbol takes about a minute. BSc & MSc · Inorganic Chemistry · Method The short answer: Combine the individual orbital angular momenta into L and the spins into S, then couple them into J. The term symbol is written 2S+1LJ. Hund’s rules then pick the ground state: maximum multiplicity first, then maximum L, then J by whether the shell is less or more than half filled. What a term symbol encodes 2S+1LJ…

The Trans Effect: Predicting the Product of Square Planar Substitution

September 4, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Reaction Mechanism The Trans Effect: Predicting the Product of Square Planar Substitution A synthesis question in coordination chemistry usually reduces to one thing — knowing which ligand directs the incoming group to the position opposite itself. BSc & MSc · Inorganic Chemistry · Concept The short answer: In square planar complexes, certain ligands strongly labilise the position trans to themselves. Arranging synthesis steps so the right ligand is present at the right time is how specific geometric isomers are made deliberately rather than as a mixture. What the effect is In a square planar complex, a ligand…

Molecular Orbital Theory for Diatomics: Bond Order and Magnetism

September 3, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Bonding Molecular Orbital Theory for Diatomics: Bond Order and Magnetism MO diagrams answer three questions at once — is the molecule stable, how strong is the bond, and is it paramagnetic. BSc & MSc · Inorganic Chemistry · Concept The short answer: Atomic orbitals combine to give bonding and antibonding molecular orbitals. Fill them by the aufbau principle, then bond order is half the difference between bonding and antibonding electrons. Unpaired electrons mean paramagnetism — which is where MO theory succeeds and valence bond theory fails. The core idea When two atomic orbitals of comparable energy and…

Cross-Coupling Reactions: Suzuki, Heck, Sonogashira and Stille

September 3, 2026

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| Chemical Science Exams, Inorganic Chemistry, Organic Chemistry

Organometallics · Entrance Exams Cross-Coupling Reactions: Suzuki, Heck, Sonogashira and Stille Four named couplings that share one palladium cycle — and differ only in what supplies the second carbon fragment. BSc & MSc · Organometallic Chemistry · Concept The short answer: All four couplings run on the same three-step palladium cycle. Oxidative addition and reductive elimination are common to every one of them; what distinguishes Suzuki, Sonogashira and Stille is only which organometallic delivers the partner group. The Heck is the exception — it has no transmetalation at all, and that single difference explains its different substrate scope and its…

Hydrogen Bonding: One Interaction, Many Consequences

September 3, 2026

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| Class 11, class 11-12 chemistry, Inorganic Chemistry

Chemical Bonding · Class 11 Hydrogen Bonding: One Interaction, Many Consequences Why water boils at 100°C, why ice floats, why ortho-nitrophenol is more volatile than the para isomer — all the same explanation. Class 11 & 12 · Chemical Bonding · Concept The short answer: A hydrogen bond needs hydrogen attached to nitrogen, oxygen or fluorine, and a lone pair on another such atom to accept it. It is about ten times stronger than an ordinary dipole interaction and roughly a tenth the strength of a covalent bond. Almost every anomaly in Class 11 and 12 physical property data traces…

Solid State for Entrance Exams: Close Packing, Voids and Band Theory

September 1, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Solid State Solid State for Entrance Exams: Close Packing, Voids and Band Theory Solid state questions are almost always either a packing calculation or a conduction argument. Both are formula-driven once the structure is identified correctly. BSc & MSc · Inorganic Chemistry · Concept and numericals The short answer: Identify the lattice type first — simple cubic, body-centred or face-centred — because everything else follows from it: atoms per unit cell, coordination number, packing efficiency and the relationship between edge length and radius. Band theory then explains conduction as the gap between the filled and empty bands….

The 18-Electron Rule and Hapticity: Counting Without Errors

August 30, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Organometallics The 18-Electron Rule and Hapticity: Counting Without Errors Electron counting is one of the few entrance-exam skills that is purely mechanical. Getting it wrong is almost always a bookkeeping slip, not a gap in understanding. BSc & MSc · Inorganic Chemistry · Method The short answer: Count the metal d electrons and add the electrons donated by each ligand. Eighteen corresponds to a filled valence shell and is the stable configuration for most low-oxidation-state transition metal complexes. Two counting conventions exist — ionic and neutral — and they give the same total provided you do not…

Crystal Field Theory: Splitting, CFSE and the Spectrochemical Series

August 30, 2026

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| Chemical Science Exams, Inorganic Chemistry

Inorganic Chemistry · Coordination Crystal Field Theory: Splitting, CFSE and the Spectrochemical Series Coordination chemistry carries more entrance-exam weight than any other inorganic topic, and crystal field theory is the engine underneath most of it. BSc & MSc · Inorganic Chemistry · Concept The short answer: An octahedral field raises the two eg orbitals and lowers the three t2g orbitals, splitting them by Δo. Whether electrons pair up or occupy the upper set depends on whether Δo exceeds the pairing energy — which is what decides high-spin versus low-spin, and therefore colour, magnetism and stability. The model in one paragraph…