Final answer:
The effective nuclear charge (Zeff) acting on the valence electrons in phosphorus is calculated by subtracting the shielding core electrons from the total nuclear charge. With 15 protons and 10 shielding core electrons, Zeff equals 5.
Step-by-step explanation:
The question asks what the effective nuclear charge (Zeff) acting on the 3s and 3p valence electrons in phosphorus is, assuming core electrons fully screen the valence electrons, and valence electrons provide no screening for each other. To calculate this, one must know the atomic number of phosphorus and the electron configuration.
Phosphorus has an atomic number of 15, meaning it has 15 protons and, in a neutral atom, 15 electrons. Its electron configuration is 1s²2s²2p¶3s²3p³. In this configuration, the inner electrons (1s, 2s, 2p) shield the valence electrons from the full charge of the nucleus.
The shielding electrons from the 1s, 2s, and 2p orbitals total 10 (2+2+6). Since we are assuming perfect shielding by the core electrons and none by the valence electrons, Zeff can be calculated as the total nuclear charge (Z) minus the shielding contributions from core electrons. Therefore, Zeff = 15 (total protons) - 10 (shielding core electrons), yielding Zeff = 5.