Which one of the following elements is NOT a Lanthanoid?

Concept:

• Our periodic table as given by Moseley and has in total 7 periods running horizontally and 18 groups running vertically.
• They are also further divided into s, p, d, and f blocks depending on the placement of the outermost electrons.
• Elements belonging to the same blocks resemble in their chemical and physical properties.
• The s block elements lie in the 1st and 2nd groups.
• The p block elements belong to groups 13-18.
• The d and f block elements lie in the middle of group numbers 3-12.

Explanation:

Lanthanides:

• The lanthanides are f block elements, as they have their last electrons in 4f subshell.
• The general electronic configuration is:

​\(\left[ {Xe} \right]4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}\)

• The lanthanides are elements having atomic numbers 58-71 from Ceriumto lutecium.
• There are 14 elements in total.
• They are called lanthanides because they resemble the element lanthanum in properties.
• They belong to period 6 but are placed at the bottom of the periodic table.
• They have stable oxidation states as +3 because two electrons are removed from the 6s and one electron from the 4f subshell.

4f-Block Elements (Lanthanides)

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• Er, Tm, Tb which are Erbium, Thulium, and Terbium respectively, belong to lanthanoids.

Hence, the element that is not a lanthanoid is Pu.

Additional Information

• Pu, plutonium belongs to the actinide series.
• It is radioactive in nature.
• They are also f block elements.
• The atomic number of plutonium is 94.