atomic number 57


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Noun1.atomic number 57 - a white soft metallic element that tarnishes readilyatomic number 57 - a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth
metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
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Most of the rare earths consist of the elements between the lanthanum (atomic number 57) and lutetium (atomic number 71), with two outliers: scandium (atomic number 21) and yttrium (atomic number 39).