Q.(c) Which of the elements whose atomic numbers are given below, cannot be accommodated in the present set up of the long form of the periodic table?

The long form of the periodic table is organized by filling electron orbitals in the order of increasing energy. Each period accommodates elements until a noble gas configuration is reached.

Period 7 ends at element 118 (oganesson), which completes the $7p^6$ configuration. This marks the natural boundary of the current periodic table structure because:

• Period 7 fills: $7s$ (2 elements), $5f$ (14 elements), $6d$ (10 elements), and $7p$ (6 elements)
• Total capacity: $2 + 14 + 10 + 6 = 32$ elements, from Z = 87 to Z = 118 …

Why the periodic table has a fixed capacity

The modern long form of the periodic table is built on quantum mechanics. Each period corresponds to filling a principal energy level, and the number of elements in each period is determined by the available orbitals:

• Period 1: $1s$ → 2 elements
• Period 2: $2s, 2p$ → 8 elements
• Period 3: $3s, 3p$ → 8 elements
• Period 4: $4s, 3d, 4p$ → 18 elements
• Period 5: $5s, 4d, 5p$ → 18 elements
• Period 6: $6s, 4f, 5d, 6p$ → 32 elements
• Period 7: $7s, 5f, 6d, 7p$ → 32 elements

The seventh period ends at element 118 (oganesson), which completes the $7p$ subshell with configuration $[Rn]5f^{14}6d^{10}7s^2 7p^6$. This marks the boundary of the current periodic table.

Checking each option

1. Element 107 (Bohrium): Falls in period 7, part of the $6d$ series. The seventh period runs from atomic number 87 (francium) to 118, so 107 fits comfortably in the existing structure.

2. Element 102 (Nobelium): A member of the actinide series (the $5f$ block), placed in period 7. Well within the current table.

3. Element 118 (Oganesson): The last element of period 7, completing the $7p^6$ configuration. This is precisely the final spot in the present setup. …