Looking ahead in Chapter 4, we explain that molecules like CH₃⁺ are Lewis acids or electron pair acceptors. Into which orbital would the new electron pair go?

Verified step by step guidance

1. Understand the context: CH₃⁺ is a carbocation, which means it has a positively charged carbon atom. This positive charge arises because the carbon atom has only six electrons in its valence shell, making it electron-deficient and a Lewis acid (electron pair acceptor).
2. Recall the electronic configuration of carbon: Carbon has an atomic number of 6, so its ground-state electronic configuration is 1s² 2s² 2p². In CH₃⁺, the carbon atom is sp² hybridized, leaving one unhybridized p orbital.
3. Visualize the molecular geometry: CH₃⁺ has a trigonal planar geometry due to sp² hybridization. The three sp² orbitals form sigma bonds with the three hydrogen atoms, while the unhybridized p orbital remains empty and perpendicular to the plane of the molecule.
4. Determine the orbital that can accept the electron pair: The empty unhybridized p orbital on the carbon atom is the orbital that can accept the incoming electron pair. This is because it is the only orbital available and not involved in bonding.
5. Conclude: The new electron pair would go into the empty p orbital of the carbon atom in CH₃⁺, which is aligned perpendicular to the plane of the molecule.

Key Concepts

Lewis Acids and Bases

Lewis acids are defined as substances that can accept an electron pair, while Lewis bases donate an electron pair. This concept is crucial for understanding how certain molecules, like CH₃⁺, interact with other species in chemical reactions. The ability of a Lewis acid to accept electrons is fundamental in predicting the outcome of reactions involving these species.

Molecular Orbitals

Molecular orbitals are formed by the combination of atomic orbitals when atoms bond together. In the case of CH₃⁺, the molecular orbitals determine where the new electron pair will reside after it is accepted by the Lewis acid. Understanding the arrangement and energy levels of these orbitals is essential for predicting the behavior of the molecule in chemical reactions.

Orbital Hybridization

Orbital hybridization is the process by which atomic orbitals mix to form new hybrid orbitals that can accommodate bonding. In CH₃⁺, the carbon atom undergoes sp³ hybridization, resulting in four equivalent orbitals that can form bonds. Recognizing the type of hybridization helps in determining the geometry of the molecule and the orbital into which the new electron pair will be accepted.