Question

4d, 5p, 5f and 6p orbitals are arranged in the order of decreasing energy. The correct option is :

• A. 6p > 5f > 4d > 5p
• B. 5f > 6p > 4d > 5p
• C. 5f > 6p > 5p > 4d
• D. 6p > 5f > 5p > 4d

Answer 1

The Correct Option is C

To solve this problem, we need to arrange the given orbitals (4d, 5p, 5f, and 6p) in order of decreasing energy. The energy of an atomic orbital can be determined using the (n+l) rule, where 'n' represents the principal quantum number and 'l' represents the azimuthal quantum number:

• The azimuthal quantum number 'l' has the following values for different orbitals:
  • s: l = 0
  • p: l = 1
  • d: l = 2
  • f: l = 3

According to the (n+l) rule:

• If two orbitals have the same (n+l) value, the one with the lower 'n' value will be lower in energy.
• If two orbitals have different (n+l) values, the one with the higher (n+l) value has higher energy.

Now, let's calculate the (n+l) values for each orbital:

• 4d: n = 4, l = 2 → (n + l) = 4 + 2 = 6
• 5p: n = 5, l = 1 → (n + l) = 5 + 1 = 6
• 5f: n = 5, l = 3 → (n + l) = 5 + 3 = 8
• 6p: n = 6, l = 1 → (n + l) = 6 + 1 = 7

Now, arrange the orbitals in order of decreasing (n+l) value, which indicates decreasing energy:

• 5f: (n + l) = 8
• 6p: (n + l) = 7
• 4d and 5p: (n + l) = 6

Since 4d and 5p have the same (n+l) value, we compare their 'n' values:

• 4d: n = 4
• 5p: n = 5

Therefore, 5p has higher energy than 4d because it has a higher 'n' value. So the order of decreasing energy is:

• 5f > 6p > 5p > 4d

Thus, the correct option is: 5f > 6p > 5p > 4d.