Question

With reference to long form of the periodic table fill in the blank spaces with appropriate words.

________ are the elements from At. no. 57 to _________ and are placed _______ the periodic table.

• A. Lanthanides, 71
• B. at the bottom of

Answer 1

Lanthanides are a group of 14 elements that follow Lanthanum (La).

• These elements begin from atomic number 57 (more precisely 58) to 71 i.e. Cerium (Ce) to Lutetium (Lu).
• These elements are placed as a separate group of 14 elements outside of the main body of the table or at the bottom of the periodic table to maintain the overall symmetry of the periodic table.

Long form of periodic Table: In the long form of the periodic table, elements are arranged in the order of their increasing atomic number in the tabular form.

• It has 18 vertical groups or columns and 7 horizontal rows or series.
• The long form of periodic table follows modern periodic law.

Therefore, lanthanides are the elements from At. no. 57 to 71 and are placed at the bottom of the periodic table.