In f-block elements, the electrons enter in which of the following shell?
Answer & explanation
Correct answer: option 2
The correct answer is option 2. Antipenultimate shell.
Let us break this down clearly with an explanation of the electron configurations and the terminology used for the shells: Shells and Subshells
Principal Quantum Number (n):
The principal quantum number \( n \) indicates the main energy level (shell) of an atom.
For example, \( n = 1, 2, 3, 4, \ldots \).
Subshells:
Within each shell, there are subshells designated by the angular momentum quantum number \( l \). For f-block elements, \( l = 3 \) (f subshell).
f-block Elements
Lanthanides: These elements fill the 4f subshell.
Actinides: These elements fill the 5f subshell.
Penultimate Shell:
The second-to-last shell (n-1). Example: For \( n = 6 \), the penultimate shell is \( n-1 = 5 \).
Antipenultimate Shell:
The third-to-last shell (n-2). Example: For \( n = 6 \), the antipenultimate shell is \( n-2 = 4 \).
Electron Configuration in f-block Elements
For lanthanides (period 6):
The principal quantum number \( n = 6 \). Electrons are added to the 4f subshell. This subshell belongs to the \( (6-2) = 4 \) shell, which is the antipenultimate shell.
For actinides (period 7):
The principal quantum number \( n = 7 \). Electrons are added to the 5f subshell. This subshell belongs to the \( (7-2) = 5 \) shell, which is the antipenultimate shell.
Summary
The f-block elements have electrons filling the f subshells of the shell that is two levels below the outermost shell. This subshell is in the antipenultimate shell (n-2).
Therefore, the electrons in f-block elements enter the antipenultimate shell.