What is the approximate effective nuclear charge (Z_{eff}) experienced by a 2s electron in a Be atom?

• A. 1.7
• B. 3.3
• C. 2.0
• D. 4.0

Answer: (C)

Verified step by step guidance

1. Identify the atomic number (Z) of beryllium (Be), which is 4, representing the total number of protons in the nucleus.
2. Understand that the effective nuclear charge (Z_{eff}) is the net positive charge experienced by an electron after accounting for the shielding effect of other electrons.
3. Use Slater's rules to estimate the shielding constant (S) for a 2s electron in Be. According to Slater's rules, electrons in the same group (2s and 2p) contribute 0.35 each, and electrons in inner shells (1s) contribute 0.85 each to the shielding.
4. Calculate the shielding constant S by summing the contributions from other electrons: the 1s electrons and the other 2s electron.
5. Apply the formula for effective nuclear charge: \(Z_{eff} = Z - S\), where Z is the atomic number and S is the shielding constant calculated in the previous step.