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| + | Chemical compounds can be fairly simple, such as water (H<sub>2</sub>O), which is just one [[oxygen]] atom and two [[hydrogen]] atoms. Many are moderately complex, like sugars, which consist of no more than a few dozen [[carbon]], oxygen, and hydrogen atoms, e.g. C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>. Some are relatively huge (still not visible to the naked eye), such as DNA, which can contain millions of atoms in one double helix crystal. |