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When the periodic table was first taught, there were 108 elements known. This has steadily increased over the years and will no doubt continue to do so. In many cases, only a few atoms have ever been created so we may never know their properties. Only elements 1 to 92 (hydrogen to uranium) occur naturally, the others have been made during nuclear reactions where heavy nuclei are made to interact with each other in particle accelerators.
The periodic table is organized into groups and periods.
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