Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
1,200 fundamentals
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is assuming the anode is always the positive terminal. In reality, oxidation always happens at the anode and reduction always at the cathode.
Memory trick: 'An-Ox, Red-Cat' — Anode Oxidation, Reduction Cathode, in every cell.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
The tendency of an electrode to gain electrons; cell EMF = E(cathode) − E(anode).
Memory trick: a positive cell EMF means the reaction is spontaneous.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is forgetting to keep reduction potentials consistent when subtracting. In reality, the tendency of an electrode to gain electrons; cell EMF = E(cathode) − E(anode).
Memory trick: a positive cell EMF means the reaction is spontaneous.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A frequent error is using standard potentials when concentrations aren't 1 M. In reality, adjusts electrode potential for non-standard concentrations.
Memory trick: ΔG = −nFE links free energy to cell voltage.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Standard cell EMF from electrode potentials. Use it when standard conditions.
E_cell = E_cathode − E_anode
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Free energy change from cell potential. Use it when n = electrons transferred, F = Faraday constant.
ΔG = −nFE
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
A galvanic cell produces electricity from a spontaneous reaction; an electrolytic cell consumes electricity to force a non-spontaneous one.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
Oxidation occurs at the anode and reduction at the cathode — in every cell, regardless of the terminal signs.
“The battery in your phone is a controlled chemical reaction pushing electrons through the circuit.”
The anode is negative in a galvanic cell but positive in an electrolytic cell; only 'oxidation at the anode' is always true.
“Every medicine, plastic and fuel is a story written in carbon.”
A permanent shift of electron density through sigma bonds due to electronegativity differences.
Memory trick: it weakens rapidly with distance — mostly the nearby atoms feel it.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is thinking the inductive effect travels undiminished along a chain. In reality, a permanent shift of electron density through sigma bonds due to electronegativity differences.
Memory trick: it weakens rapidly with distance — mostly the nearby atoms feel it.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is believing the separate resonance structures actually exist and interconvert. In reality, delocalisation of electrons over several atoms, giving extra stability.
Memory trick: the real molecule is a single averaged hybrid of all structures.
“Every medicine, plastic and fuel is a story written in carbon.”
Electrophiles are electron-poor (seek electrons); nucleophiles are electron-rich (donate electrons).
Memory trick: nucleophile = nucleus-loving = electron donor; electrophile = electron-loving = acceptor.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is swapping the two definitions. In reality, electrophiles are electron-poor (seek electrons); nucleophiles are electron-rich (donate electrons).
Memory trick: nucleophile = nucleus-loving = electron donor; electrophile = electron-loving = acceptor.
“Every medicine, plastic and fuel is a story written in carbon.”
A frequent error is ranking a primary carbocation as more stable than a tertiary one. In reality, order 3° > 2° > 1°, because alkyl groups donate electrons and stabilise the positive charge.
Memory trick: more alkyl groups → more stable carbocation (hyperconjugation + inductive).
“Every medicine, plastic and fuel is a story written in carbon.”
The inductive effect works through sigma bonds and fades with distance; resonance works through pi systems and can act over long conjugation.
“Every medicine, plastic and fuel is a story written in carbon.”
SN1 goes through a carbocation in two steps (favoured by 3° substrates); SN2 is a one-step backside attack (favoured by 1° substrates).
“Every medicine, plastic and fuel is a story written in carbon.”
They don't flip back and forth — the molecule is one stable resonance hybrid.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
Alkanes are saturated (only single bonds); alkenes and alkynes are unsaturated (double or triple bonds).
Memory trick: double/triple bonds are reactive sites — unsaturated hydrocarbons react more readily.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
A frequent error is thinking unsaturated hydrocarbons are less reactive than alkanes. In reality, alkanes are saturated (only single bonds); alkenes and alkynes are unsaturated (double or triple bonds).
Memory trick: double/triple bonds are reactive sites — unsaturated hydrocarbons react more readily.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
A frequent error is reversing it, except in the peroxide (anti-Markovnikov) effect. In reality, when HX adds to an alkene, H attaches to the carbon that already has more hydrogens.
Memory trick: 'the rich get richer' — the H-rich carbon gains the H.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
Extra stability of planar, cyclic, fully-conjugated rings with (4n+2) pi electrons (benzene).
Memory trick: benzene prefers substitution because addition would destroy its aromatic stability.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
A frequent error is expecting benzene to undergo addition like an alkene. In reality, extra stability of planar, cyclic, fully-conjugated rings with (4n+2) pi electrons (benzene).
Memory trick: benzene prefers substitution because addition would destroy its aromatic stability.
“Petrol, cooking gas and candle wax are all hydrocarbons — just different chain lengths.”
An alkane has only single C–C bonds (saturated, reacts by substitution); an alkene has a C=C double bond (unsaturated, reacts by addition).