Question

Justify that the fifth period of the periodic table should have 18 elements on the basis of quantum numbers.

Answer 1

The fifth period of the periodic table has 18 elements.

5^th period starts from Rb to Xe (18 elements).

5^th period starts with principal quantum number n = 5 and l = 0, 1, 2, 3 and 4.

When n = 5, the number of orbitals = 9.

1 for 5s, 5 for 4d, 3 for 5p

The total number of orbitals = 9.

Total number of electrons that can be accommodated in 9 orbitals = 9 × 2 = 18.

Hence the number of elements in the 5^th period is 18.