Before you can read the parent topic, you must own every symbol it throws at you. We build each one from nothing, in the order they depend on each other.
A p-orbital is a dumbbell — two lobes, like a balloon pinched in the middle, pointing along one axis. An atom has three of them (one along each of the x,y,z directions).
The crucial question the parent page hammers: which direction does the lone pair point?
If the lone pair sits in an upright p-orbital (perpendicular to the ring), it joins the π loop → counts as 2 π electrons (furan's O, pyrrole's N, cyclopentadienyl's C⁻).
If it sits in an in-plane sp2 orbital (lying flat, pointing outward), it does not join the loop → not counted (pyridine's N, furan's second lone pair).
Test yourself — cover the right side of each line.
What is aromaticity in one sentence?
The extra stability a ring gains when its π electrons are delocalised all around a closed loop AND total a magic number (4n+2).
What is an orbital, and how many electrons fits in one?
A fuzzy region where an electron is likely found; max 2 electrons.
What shape is a p-orbital and why does it matter here?
A dumbbell (two lobes above/below); side-by-side p-orbitals build the π loop.
Difference between a σ bond and a π bond?
σ sits directly between two nuclei (single bond); π is side-by-side p-overlap above/below the plane (the part of a double bond).
What does "π electrons" mean?
The electrons in the sideways p-overlap clouds — the loop-electrons free to roam the ring.
What does "planar" mean and why is it required?
All ring atoms lie in one flat plane; only then are the p-orbitals parallel enough to overlap into a continuous loop.
What is the difference between sp3 and sp2 hybridisation?
sp3 uses all three p-orbitals (tetrahedral, none left over); sp2 uses two p-orbitals (flat triangle) leaving one upright p-orbital.
What does sp2 hybridisation leave over, and where does it point?
One untouched p-orbital standing perpendicular to the flat 120∘ triangle.
What does "cyclic" mean as an aromaticity condition?
The atoms form a closed ring you can trace back to the start without lifting your finger.
What does "conjugated" require?
Overlapping p-orbitals on adjacent atoms with no break (no sp3 atom interrupting).
What does delocalisation mean and why is it stabilising?
Electrons smeared over the whole system, not one bond; spreading a wave lowers its energy.
When does a lone pair count as 2 π electrons?
Only when it sits in an upright p-orbital aligned with the ring; in-plane lone pairs don't count.
What is a molecular orbital (vs an atomic orbital)?
A combined electron cloud belonging to the whole molecule (atomic p-orbitals merged); an atomic orbital belongs to one atom.
What does "degenerate" mean?
Molecular orbitals at exactly the same energy (same ladder rung); symmetric rings give degenerate pairs.
Is n the number of π electrons?
No — n is a whole-number counter (0,1,2,…) of filled degenerate pairs; the electron count is 4n+2.
Define aromatic vs antiaromatic.
Aromatic = cyclic/planar/conjugated with 4n+2 π e⁻ (extra stable); antiaromatic = same but 4n π e⁻ (destabilised).
List the first four magic numbers.
2, 6, 10, 14.
What do Ek, α, β, k and N represent?
Ek = energy of the k-th molecular orbital; α = isolated p-orbital energy; β = (negative) stabilising overlap energy; N = number of ring atoms; k = MO label (0,±1,±2,…).
