Purdue still has an old General Chemistry Help page that explains the difference between atoms and ions with almost no ceremony: count the protons, count the electrons, and see whether the charges balance. The page looks modest because it was built to teach chemistry, not to audition for a redesign.
Visit Purdue’s Atoms vs. Ions page
The explanation starts from electrically neutral atoms, where the number of electrons matches the number of protons, then shows how losing or gaining electrons creates charged ions. Sodium and chlorine provide the practical example: neutral sodium metal and chlorine gas are highly reactive substances, while sodium and chloride ions can sit together in ordinary table salt without making dinner unusually exciting.
That page is only one piece of a much larger teaching site.
A Whole Chemistry Course Built From Links
Purdue’s General Chemistry material contains topic reviews covering measurements, stoichiometry, gases, thermochemistry, atomic structure, ionic and covalent compounds, metals, acids and bases, oxidation-reduction reactions and other introductory material.
The broader help site also links course information, laboratory material, problem-solving resources, glossaries, old tests and lecture demonstrations. Instead of hiding everything inside a learning-management system that requires an account and a current enrollment, much of the instructional material lives as ordinary public webpages.
Some surrounding pages reveal their age more clearly than the chemistry does. Old software-help material references Netscape, Eudora Lite and VRML browsers. A lecture-demonstration page carries a 2002 update date and includes the sort of browser and frame instructions that used to be normal housekeeping for educational websites.
The Content Outlived the Interface
There is a useful lesson for webmasters here. The atoms-and-ions page does not need JavaScript, animation, a user account or an application framework to explain a chemical idea. Its usefulness is mostly in the writing, diagrams and links.
That simplicity has aged surprisingly well. Browser fashions changed repeatedly around it while the basic educational job remained the same.
For chemistry students, the material is still a quick reference. For Internet-history researchers, the larger site preserves an era when universities often published course resources directly onto the open Web, where a student twenty years later can still stumble into them through a search engine.