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Welcome! We are an encyclopedia project, and more. We are a different sort of Web 2.0 project: We aim at credibility and quality, not just quantity. Both the general public and credentialed experts are encouraged to get involved. We use our real names, not pseudonyms. We're collegial. We have added over 3,800 articles (and many subpages) since November 2006. Read our first year progress report and press release. Join us! New authors and editors welcome! A human being will respond usually within a few hours. Start here. Learn about us For readers: About the Citizendium For authors: The Author Role For editors: The Editor Role Initiatives Core Articles - tackle high priority topics Recruitment - help invite others to join Subpages - add other types of info to CZ Eduzendium - students write CZ articles for credit Support us We're a 501(c)(3) non-profit, and we need your support. If you shop at Amazon.com or Barnes & Noble, do so through our links! We'll get donations at no cost to you. (read more) - Search All Products.	Some of our finest [ about ] Approved Articles Developed Articles (over 700) Article of the Week [ about ] Chemistry is the science of materials. Chemists consider that all of the materials in the world are matter, primarily made up of atoms. The combination of at least two atoms connected by a chemical bond leads to molecules. Ions are derived from atoms or molecules by loss or gain of one or more electrons leading to charged particles. Salts are composed of cations (positively charged ions) and anions (negatively charged ions), so that the substance or material is neutrally charged (without net charge). Chemists use their view of matter at the atomic to molecular level to explain how different materials interact, and how they change under varying conditions. [more...] New Draft of the Week [ about ] Augustin-Louis Cauchy (Paris, August 21, 1789 – Sceaux, May 23, 1857) was one of the most prominent mathematicians of the first half of the nineteenth century. He was the first to give a rigorous basis to the concept of limit. His criterion for the convergence of sequences defines sequences that are now known as Cauchy sequences. This notion has led to the fundamental mathematical concept of a complete space. The Cauchy condition for the convergence of series can be found in any present-day textbook on calculus. Probably Cauchy is most famous for his singlehanded development of complex function theory, with Cauchy's residue theorem as the fundamental result.[more...]