57
The lanthanide series.
Two series of inner transition elements are the lanthanides (from atomic number 57 to 71) and actinides (from atomic number 89 to 103).
Promethium (Pm) is the only synthetic element in the lanthanide series. It is not found naturally on Earth and is typically produced in nuclear reactors.
The smallest atomic number and atomic weight for a lanthanide is lanthanum itself, element 57. The smallest atomic size is lutecium element 71; the lanthanides steadily decrease in atomic radius through the series, and the smallest is the last of them.
its in the Lanthanide series
Thulium belongs to the lanthanide series in the periodic table, which is often referred to as the rare earth metals.
Lutetium is one of the first inner transition series metals, sometimes called "lanthanides" because all of them have chemistry very similar to that of lanthanum, the first member of the series.
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cerium is atomic number 58 element and is in lanthanoide family and is a transition metal
The chemical element with atomic number 57 is Lanthanum (La). It is a Lanthanide, as it is what the rest of the Lanthanides are based on. It has 57 electrons in 6 shells. It is naturally occuring and non-radioactive.
They are used for making alloys
Earth