What is the electron configuration of the element in the 4th period of Group 5A (IUPAC Group 15), using an appropriate noble gas symbol for the core electrons?
(A) [Kr] 4s2 3d10 4p5
(B) [Ar] 4s2 3d10 4p3
(C) [Ar] 4s2 4p3
(D) [Kr] 4s2 4p5
The Correct Answer and Explanation is :
Correct Answer: (B) [Ar] 4s² 3d¹⁰ 4p³
Explanation:
To determine the electron configuration of the element in the 4th period of Group 5A (IUPAC Group 15), follow these steps:
1. Identify the element:
- Group 5A (Group 15): This group includes elements with 5 valence electrons in the outermost shell.
- 4th Period: The 4th period includes elements where the principal quantum number ( n = 4 ).
- The element in Group 15 and the 4th period is arsenic (As).
2. Understand its electron configuration:
- The electron configuration is built by filling orbitals in order of increasing energy:
- ( 1s ), ( 2s ), ( 2p ), ( 3s ), ( 3p ), ( 4s ), ( 3d ), ( 4p ).
- Using the noble gas shorthand notation:
- Core electrons are represented by the electron configuration of the preceding noble gas (argon, ( [Ar] ), in this case).
- Electrons beyond ( [Ar] ) are added to the ( 4s ), ( 3d ), and ( 4p ) orbitals.
3. Determine the configuration:
- After ( [Ar] ), the ( 4s ) orbital is filled with 2 electrons:
[ [Ar] 4s^2 ] - Next, the ( 3d ) orbital is filled with 10 electrons:
[ [Ar] 4s^2 3d^{10} ] - Finally, the ( 4p ) orbital gains 3 electrons to account for Group 15’s 5 valence electrons:
[ [Ar] 4s^2 3d^{10} 4p^3 ]
4. Eliminate incorrect options:
- (A) ( [Kr] ): Incorrect because the core noble gas should be ( [Ar] ) for the 4th period.
- (C) ( [Ar] 4s^2 4p^3 ): Incorrect because it ignores the ( 3d ) orbital.
- (D) ( [Kr] 4s^2 4p^5 ): Incorrect noble gas and wrong electron count.
Thus, the correct configuration is ( [Ar] 4s^2 3d^{10} 4p^3 ), corresponding to (B).