Write the electron configuration for phosphorus and underline the valence electrons. 1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
The Correct Answer and Explanation is:
Electron Configuration for Phosphorus (P):
Phosphorus has an atomic number of 15, meaning it has 15 electrons in its neutral state. The electron configuration is written by filling orbitals in order of increasing energy levels.
Electron configuration:
1s² 2s² 2p⁶ 3s² 3p³
Valence electrons (underlined):
1s² 2s² 2p⁶ 3s² 3p³
Explanation:
The electron configuration of an element describes the distribution of its electrons among the various atomic orbitals. Phosphorus, with an atomic number of 15, has 15 electrons arranged in a specific order based on the Aufbau principle, Pauli exclusion principle, and Hund’s rule. These rules govern how electrons occupy orbitals:
- Aufbau Principle: Electrons fill orbitals starting from the lowest energy level.
- Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.
- Hund’s Rule: Electrons will fill degenerate orbitals (orbitals of the same energy) singly first before pairing up.
Beginning with the lowest energy orbital:
- The 1s orbital is filled first: 2 electrons → 1s²
- Then the 2s orbital: 2 electrons → 2s²
- Next, the 2p orbital: 6 electrons → 2p⁶
- Followed by the 3s orbital: 2 electrons → 3s²
- Finally, the 3p orbital: 3 electrons → 3p³
This gives the full configuration as 1s² 2s² 2p⁶ 3s² 3p³.
The valence electrons are the electrons located in the outermost shell, which for phosphorus is the third energy level (n = 3). These include the electrons in the 3s and 3p orbitals, totaling 5 valence electrons (3s² 3p³). Valence electrons play a critical role in chemical bonding and reactivity.
