Rare Earth Elements by atomic number and molecular weight:

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Atomic Number Name Molecular Weight
57 Lanthanum 138.9055
58 Cerium 140.116
59 Praseodymium 140.9077
60 Neodymium 144.242
61 Promethium 145
62 Samarium 150.36
63 Europium 151.964
64 Gadolinium 157.25
65 Terbium 158.9253
66 Dysprosium 162.500
67 Holmium 164.9303
68 Erbium 167.259
69 Thulium 168.9342
70 Ytterbium 173.04
71 Lutetium 174.967

Note that promethium is radioactive and does not occur naturally. It is produced synthetically.

The rare earth elements are also classified into three groups based on their atomic number:

Light rare earth elements (LREE): La, Ce, Pr, Nd, Pm

Intermediate rare earth elements (MREE): Sm, Eu, Gd, Tb, Dy

Heavy rare earth elements (HREE): Ho, Er, Tm, Yb, Lu

The LREE are the most abundant rare earth elements, while the HREE are the least abundant.
The MREE are intermediate in abundance.

References:

Rare Earth Elements: Chemistry, Fate and Environmental Impact: https://www.envchemgroup.com/rare-earth-elements.html by the Royal Society of Chemistry

History and Future of Rare Earth Elements: https://sciencehistory.org/education...istory-future/ by the Science History Institute

Rare Earth Elements: https://www.britannica.com/science/rare-earth-element from Encyclopedia Britannica

Rare Earth Elements: https://en.wikipedia.org/wiki/Rare-earth_element from Wikipedia

Extraction and separation of heavy rare earth elements: A review
https://www.sciencedirect.com/scienc...83586621009734

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