"Atoms want a full outer shell" is retired as an explanation

Atoms react in order to achieve a full outer shell / a noble gas configuration. Sodium "wants to lose" one electron; chlorine "wants to gain" one. Bonding happens because atoms are trying to become stable.

Bonding is electrostatics plus energy minimisation. An ionic bond is "the electrostatic attraction between oppositely charged ions" (Structure 2.1.2); a covalent bond is "the electrostatic attraction between a shared pair of electrons and the positively charged nuclei" (Structure 2.2.1). Note the wording — both definitions are electrostatic. Whether a species forms depends on the overall energy balance (which the Born–Haber cycle, Reactivity 1.2.5, makes explicit: ionisation energy is endothermic and by itself unfavourable; it is lattice enthalpy that pays for it). The octet is a useful pattern that correlates with stability, not a cause.

The direction of explanation reverses. GCSE: "it forms a bond because it gets a full shell." IB: "the full shell is what you observe because that arrangement happens to be low in energy." IB then immediately shows you cases where the octet is violated legitimately — expanded octets (Structure 2.2.13: SF₆, PCl₅, XeF₄), electron-deficient BF₃, odd-electron radicals (Reactivity 3.3), and formal charge analysis (Structure 2.2.14) which sometimes prefers a Lewis structure that breaks the octet.

The octet rule is a genuinely excellent heuristic for period 2 and it lets 15-year-olds draw correct diagrams. It is a legitimate teaching model that becomes a liability only when treated as a mechanism.

This is the single most documented alternative framework in chemistry education — Taber calls it the "octet framework" and the "full outer shells explanatory principle", and shows it persists into university (Taber 1998, 2024). Symptoms: writing "the sodium atom donates its electron to the chlorine atom so they both have full shells" as an explanation of NaCl's lattice; believing an Na⁺ ion is specially bonded to "its" Cl⁻ (the molecular framework for ionic bonding); asserting that reactions occur because atoms "want" something (anthropomorphism); refusing to accept SF₆ exists; being unable to explain why noble gases are unreactive without circularity. It also makes Born–Haber cycles (HL) incomprehensible, because the student expects ionisation to be energy-releasing.