Complete the following statements regarding effective nuclear charge (Zeff) for the phosphorus atom:

I. The Zeff for a valence electron in a phosphorus atom is
[ Select ]
less than
equal to
greater than
the Zeff for a valence electron in a magnesium atom.
II. The Zeff for a 1s electron in a phosphorus atom is
[ Select ]
equal to
less than
greater than
the Zeff for a 2s electron in a phosphorus atom.

01A

Question

Complete the following statements regarding effective nuclear charge (Zeff) for the phosphorus atom:

I. The Zeff for a valence electron in a phosphorus atom is 
[ Select ]
less than
equal to
greater than
 the Zeff for a valence electron in a magnesium atom.
II. The Zeff for a 1s electron in a phosphorus atom is 
[ Select ]
equal to
less than
greater than
 the Zeff for a 2s electron in a phosphorus atom.

01A

BlackTom AI · Accepted Answer

Let's examine the two statements about effective nuclear charge Zeff step by step, comparing the relevant electrons and atoms.
First, consider Statement I: Zeff for a valence electron in phosphorus versus a valence electron in magnesium.
- Phosphorus has atomic number Z = 15, with valence electrons in the 3s and 3p orbitals. Magnesium has Z = 12, with valence electrons in the 3s orbital.
- Zeff roughly tracks the total nuclear charge felt by the electron after accounting for shielding by inner electrons. All else equal, increasing the nuclear charge while similar shielding leads to a larger Zeff for the valence electrons.
- Therefore, a phosphorus valence electron experiences a stronger pull from the nucleus than a magnesium valence electron, making Zeff(phosphorus valence) greater than Zeff(magnesium valence).
- Conclusion for Statement I: greater than.

Second, consider Statement II: Zeff for a 1s electron in phosphorus versus a 2s electron in phosphorus.
- The 1s electron is closest to the nucleus and experiences the least shielding, so it feels a stronger effective nuclear charge than electrons in higher shells.
- The 2s electron, while still fairly close, is more shielded by the 1s electrons and other inner electrons, reducing its Zeff relative to the 1s electron.
- Consequently, Zeff(1s) is greater than Zeff(2s).
- Conclusion for Statement II: greater than.

Summarizing the option-by-option reasoning:
- For the first statement, the correct choice is that Zeff in phosphorus valence is greater than Zeff in magnesium valence, because the higher nuclear charge in phosphorus outweighs the relatively similar shielding for valence electrons.
- For the second statement, the correct choice is that Zeff for a 1s electron in phosphorus is greater than that for a 2s electron in phosphorus, due to reduced shielding and greater proximity to the nucleus for the 1s electron.

Therefore, both statements are true with the selected answers being 'greater than' for each blank.

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