How does the shielding effect alter the ionization energy of an atom?

• A. It increases the ionization energy by increasing the attraction between the nucleus and valence electrons.
• B. It has no effect on the ionization energy of an atom.
• C. It causes the ionization energy to increase only for transition metals.
• D. It decreases the ionization energy by reducing the effective nuclear charge experienced by valence electrons.

Answer: (D)

Verified step by step guidance

1. Understand that ionization energy is the energy required to remove an electron from an atom.
2. Recognize that the shielding effect occurs when inner electrons repel outer (valence) electrons, reducing the full positive charge of the nucleus felt by these valence electrons.
3. Know that this reduction in effective nuclear charge (\(Z_{eff}\)) means valence electrons are held less tightly by the nucleus.
4. Since valence electrons experience less attraction due to shielding, less energy is needed to remove them, which means ionization energy decreases.
5. Therefore, the shielding effect decreases the ionization energy by lowering the effective nuclear charge experienced by valence electrons.