Which of the following best describes the effective nuclear charge (Z_eff) experienced by a valence electron in a bromine (Br) atom?

• A. It is equal to the total number of protons in bromine.
• B. It is less than the actual nuclear charge due to shielding by inner electrons.
• C. It is greater than the actual nuclear charge because of electron-electron repulsion.
• D. It is zero because all nuclear charge is completely shielded.

Answer: (B)

Verified step by step guidance

1. Understand that the effective nuclear charge (\(Z_{\text{eff}}\)) is the net positive charge experienced by an electron in an atom, considering both the attraction from the nucleus and the repulsion from other electrons.
2. Recall that the actual nuclear charge (\(Z\)) is the total number of protons in the nucleus, which for bromine (Br) is 35.
3. Recognize that inner (core) electrons shield the valence electrons from the full positive charge of the nucleus, reducing the effective nuclear charge felt by valence electrons.
4. Note that electron-electron repulsion among valence electrons does not increase \(Z_{\text{eff}}\); instead, it can slightly reduce the attraction felt by each electron.
5. Conclude that the effective nuclear charge experienced by a valence electron in bromine is less than the actual nuclear charge due to shielding by inner electrons.