Lutetium is the chemical element with atomic number and chemical symbol . It is a dense rare-earth element whose ordinary chemistry is dominated by the oxidation state. The neutral atom has a filled shell with outer occupancy.[ref]
Its close chemical similarity to neighbouring rare earths makes separation difficult. This illustrates why identifying a new element and obtaining a pure metallic specimen are different experimental achievements. Element identity is fixed by nuclear charge, whereas similar outer-electron chemistry controls the practical separation.
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