Rank the following elements by effective nuclear charge, Z_eff, for a valence electron. Highest Z_eff Lowest Z_eff Pb Bi Po Rn Ba

The periodic table tendency for effective nuclear charge:

1. Increase across a period (due to increasing nuclear charge with no accompanying increase in shielding effect)  
2. Decrease down a group (although nuclear charge increases down a group, shielding effect more than counters its effect).
3. 3.Therefore if we rank the elements from highest Z_eff to lo lowest Z_eff we get

Highest Z_eff  Rn --> Po --> Bi --> Pb --> Ba Lowest Z_eff

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