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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 3,100 articles (and many subpages) since November 2006. Join us! New authors and editors welcome! A human being will respond usually within a few hours. 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 What's Your Article? - a place to display your best Support us We're a 501(c)(3) non-profit, and we need your support. If you shop at Amazon or Barnes & Noble and you access these sites by the links provided here, we'll be getting donations at no cost to you (read more) - Search All Products.	Some of our finest [ about ] Approved Articles Developed Articles (over 600) Draft of the Week [ about ] The Rottweiler is a large breed of dog known for its great physical strength and strong protective instinct. The breed was once employed widely to guard, herd, and pull carts, and its kennel club classification, usually in the working dog group, reflects this. Although still sometimes put to work, especially as police dogs, most rottweilers today serve as human companions or family pets, where their natural instincts manifest as a strong protectiveness toward those they consider their own. [more...] New Draft of the Week [ about ] Oxygen (chemical symbol O) is the most abundant (46.6%) chemical element of the lithosphere (the crust and the uppermost mantle of the earth). It is a constituent of water (H2O) and of rocks and sand in the form of silicon dioxide SiO2 (silica). A volume of earth atmosphere consists of 21% of the oxygen molecule O2. The O-atom has nuclear charge 8e, where e is the elementary charge, and 8 electrons, occupying the eighth position in the Periodic Table of Elements, i.e., its atomic number Z is eight. Atomic oxygen is very reactive, so that the element does not occur naturally in free form, but only in compounds. [more...]