medium · MCAT chem-phys

When comparing Oxygen (Z = 8) and Selenium (Z = 34) in the context of antioxidant molecules, Selenium is found to have a larger atomic radius. This is primarily because:

1. Oxygen is a gas at room temperature, which naturally compresses its atomic volume.
2. Oxygen has a higher effective nuclear charge which pulls its shells further out.
3. Selenium's valence electrons experience less shielding from inner electrons.
4. Selenium has more occupied electron shells than Oxygen.

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