How Atoms Join

Five parts on what a chemical bond actually is, opening by refusing the sentence every textbook uses. Atoms do not want full outer shells: they have no wants, and that phrasing swaps a mechanism for a motive. The argument instead starts from the elements that form almost no compounds, notes that what helium, neon and argon share is a filled outer shell, and gets to the real reason — such an arrangement is lower in energy, and systems settle into lower arrangements the way water runs downhill. It also puts the direction the right way round: breaking a bond costs energy and making one releases it, with the hydrogen combustion sum worked through in numbers so the claim is checkable. The second part turns transfer into arithmetic, so that the charge on an ion and then the formula of the compound can be worked out from a group number rather than remembered. The third sets transfer against sharing and shows what decides between them. The fourth takes the trap almost everyone falls into — salt melts at 801 °C and ice at 0 °C, and the bonds inside a water molecule are strong — by establishing that melting separates particles and never breaks a molecule open, so a melting point reports the structure rather than the strength of any bond. The last part reaches the third kind of bonding and the one case where a blow does not shatter anything: a lattice of positive ions in a pool of electrons that belong to none of them, which is why metals bend, why alloys are harder, and why a spoon feels cold.