Arrange these chemical elements in the correct order by their atomic number, from lowest to highest. The periodic table organizes all known chemical elements by their atomic number - The number of protons in the nucleus of an atom of that element. Hydrogen is element number one with a single proton; helium is number two; and so on up through oganesson, the heaviest known element at number 118. The periodic table's rows and columns are not arbitrary - Elements in the same column share similar chemical properties because they have the same number of electrons in their outermost shell. This remarkable organizing principle, first proposed by Dmitri Mendeleev in 1869, is one of the great intellectual achievements of chemistry. Test your periodic table knowledge by ordering these familiar elements correctly.
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Drag items into the correct order, then hit Submit.