Rust is paramagnetic and differs from black iron oxide, which is used in magnetic recording media, due to its chemical composition; rust is Fe2O3 while black iron oxide is Fe3O4. The discussion highlights how a single atom change can significantly alter a compound's properties, using various examples like ozone versus oxygen and sodium chloride versus its individual elements. The conversation also touches on the nature of water, questioning why it remains a liquid rather than a gas, attributing this to hydrogen bonding that increases molecular cohesion. The importance of understanding these chemical differences is emphasized throughout the discussion. Overall, the thread illustrates how small molecular changes can lead to vastly different physical properties.