Despite the expected decrease in atomic size, there is an...

Name: Problem 33, Chapter 14: Chemistry: The Molecular Nature of Matter and Change
Uploaded: 2020-09-23T18:29:42-08:00
Duration: 1 min 13 s
Channel: Lottie Adams
Description: Despite the expected decrease in atomic size, there is an unexpected drop in the first ionization energy between Groups 2A(2) and 3A(13) in Periods 2 through 4. Explain this pattern in terms of electron configurations and orbital energies.

Despite the expected decrease in atomic size, there is an unexpected drop in the first ionization energy between Groups 2A(2) and 3A(13) in Periods 2 through 4. Explain this pattern in terms of electron configurations and orbital energies.

Key Concepts

Orbital Energy and Ionization Energy

The energy required to remove an electron (ionization energy) is related to the energy level of its orbital. Electrons in lower energy, well-penetrated orbitals (such as s orbitals) are more strongly bound to the nucleus and require more energy for removal, whereas electrons in higher energy, less penetrating orbitals (like p orbitals) are more weakly held, leading to a lower ionization energy.

Effective Nuclear Charge

Effective nuclear charge is the net positive charge an electron experiences after accounting for the repulsive effects of other electrons. Even with a decrease in atomic size, electrons in less penetrating orbitals (like p orbitals) feel a lower effective nuclear charge due to increased shielding. This reduced effective pull is key to understanding the drop in ionization energy when moving from Group 2A to Group 3A.

Orbital Penetration and Shielding

Orbital penetration refers to how close an electron can get to the nucleus, while shielding describes how inner electrons reduce the effective nuclear charge experienced by outer electrons. Electrons in s orbitals penetrate closer to the nucleus and experience less shielding compared to p electrons, which makes them more tightly bound. This distinction helps explain why an electron in a p orbital (found in Group 3A) is removed more easily, resulting in a lower ionization energy.

Electronic Configuration

Electronic configuration describes the arrangement of electrons in an atom’s orbitals. In this context, moving from Group 2A to Group 3A involves a change from having a fully filled s subshell to adding an electron in a p subshell. This difference in configuration affects how strongly electrons are held, influencing ionization energy trends.

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