Elements: In the space below, write the unabbreviated electron configurations of the following elements: – Sodium: 1s^2 2s^2 2p^6 3s^1 – Iron: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6 – Bromine: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^5 – Barium: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 – Neptunium: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 4f^14 5d^10 6p^6 7s^2 5f^4 In the space below, write the abbreviated electron configurations of the following elements: – Cobalt: [Ar] 4s^2 3d^7 – Silver: [Kr] 5s^1 4d^10 – Tellurium: [Kr] 5s^2 4d^10 5p^4 – Radium: [Rn] 7s^2 – Lawrencium: [Rn] 5f^14 7s^2 6d^1 Determine what elements are denoted by the following electron configurations: – 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 4f^14 5d^10 6p^6 7s^2 5f^2: Sulfur – 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 4f^14 5d^10 6p^6 7s^2 5f^4 6d^0: Einsteinium Determine which of the following electron configurations are not valid: – 1s^2 2s^2 2p^2 0s^3 3p^4 5d^4: Not valid – 4d^4 4p^5: Not valid
The Correct Answer and Explanation is:
Below are the correct answers and a detailed explanation of the principles governing electron configurations.
Unabbreviated Electron Configurations
- Sodium (Na): 1s² 2s² 2p⁶ 3s¹
- Iron (Fe): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
- Bromine (Br): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵
- Barium (Ba): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²
- Neptunium (Np): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁴ 6d¹
Abbreviated Electron Configurations
- Cobalt (Co): [Ar] 4s² 3d⁷
- Silver (Ag): [Kr] 5s¹ 4d¹⁰
- Tellurium (Te): [Kr] 5s² 4d¹⁰ 5p⁴
- Radium (Ra): [Rn] 7s²
- Lawrencium (Lr): [Rn] 7s² 5f¹⁴ 6d¹
Elements Denoted by Electron Configurations
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f²: Thorium (Th)
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f⁴: Uranium (U)
Invalid Electron Configurations
- 1s² 2s² 2p² 0s³ 3p⁴ 5d⁴: Not Valid
- 4d⁴ 4p⁵: Not Valid
Electron configurations are a fundamental notation in chemistry that describes the specific arrangement of electrons in an atom’s orbitals. This arrangement determines an element’s chemical behavior, bonding patterns, and placement on the periodic table. The notation follows a set of established rules derived from quantum mechanics.
The Aufbau principle (German for “building up”) dictates that electrons populate the lowest energy orbitals available before filling higher energy ones. The standard order of filling is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, and they must have opposite spins. Finally, Hund’s rule directs that for a subshell with multiple orbitals of the same energy (like the three p-orbitals or five d-orbitals), electrons will fill each orbital singly before any orbital is doubly occupied.
To identify an element from its configuration, one must sum the electrons (the superscripts) to find the total, which equals the atomic number (Z) for a neutral atom. For example, the configuration ending in …7s² 5f² contains 90 electrons in total ([Rn] core = 86, plus 2+2), identifying it as Thorium (Th, Z=90). Similarly, a configuration with 92 total electrons (…7s² 5f⁴) corresponds to Uranium (U).
A configuration is considered invalid if it violates these core principles. The notation 1s² 2s² 2p² 0s³ 3p⁴ 5d⁴ is invalid for multiple reasons: the principal quantum number “n” cannot be zero, and an s-orbital cannot hold three electrons. The configuration 4d⁴ 4p⁵ is also invalid because it is incomplete and violates the Aufbau principle, as the 4p subshell fills before the 5s and 4d subshells.
