MOT Flashcards
(18 cards)
What are the postulates of Molecular Orbital Theory (MOT)?
- Atomic orbitals combine to form molecular orbitals.
- Electrons fill molecular orbitals based on the Aufbau principle.
- Molecular orbitals can be bonding (lower energy) or antibonding (higher energy).
- The number of molecular orbitals equals the number of atomic orbitals involved.
How is bond order calculated in MOT?
Bond order = (Number of electrons in bonding orbitals - Number of electrons in antibonding orbitals) / 2.
What is the difference between paramagnetism and diamagnetism?
Paramagnetism: Attracted to a magnetic field due to unpaired electrons.
Diamagnetism: Repelled by a magnetic field due to all electrons being paired.
Define paramagnetism and diamagnetism.
Paramagnetism: Substances with unpaired electrons, attracted to magnetic fields.
Diamagnetism: Substances with all paired electrons, repelled by magnetic fields.
What is the energy order for molecules with atomic number ≤ 7 (like N₂)?
σ1s < σ°1s < σ2s < σ°2s < π2pᵧ = π2pz < σ2pₓ < π°2pᵧ = π°2pz < σ°2pₓ
What is the energy order for molecules with atomic number ≥ 8 (like O₂)?
σ1s < σ°1s < σ2s < σ°2s < σ2pₓ < π2pᵧ = π2p𝓏 < π°2pᵧ = π°2p𝓏 < σ°2pₓ
WTF
How do you calculate bond order for O₂?
For O₂: Bond order = (8 electrons in bonding - 4 electrons in antibonding) / 2 = 2. So, bond order = 2.
What is the difference between bonding and antibonding molecular orbitals?
Bonding orbitals: Lower energy, result in attractive interaction between atoms.
Antibonding orbitals: Higher energy, result in repulsive interaction between atoms.
For a molecule with equal numbers of electrons in bonding and antibonding orbitals, what is its bond order?
Bond order = 0 (No bond).
✨ “Compare the relative energies of the molecular orbitals σ°(2p_z), π°(2p_x), and π°(2p_y). Which of these orbitals lies higher in energy, and why?”
In molecules where the atomic number is ≤ 7 (like N₂, C₂, B₂), the π°(2p_x) and π°(2p_y) orbitals are lower in energy than the σ°(2p_z) orbital. This is due to s–p mixing (or orbital mixing), which occurs significantly in lighter elements. The energy gap between 2s and 2p orbitals is small, so their interaction causes the σ(2p_z) orbital to be pushed above the degenerate π(2p) orbitals.
Thus,
π°(2p_x) = π°(2p_y) < σ°(2p_z)
What does a higher bond order indicate?
A higher bond order indicates greater bond strength and stability.
What is the bond order of O₂, and is it paramagnetic or diamagnetic?
Bond order = 2.
Paramagnetic (due to 2 unpaired electrons).
How do you calculate bond order for O₂⁻?
For O₂⁻: Bond order = (8 bonding electrons - 5 antibonding electrons) / 2 = 1.5.
What is the bond order of N₂?
For N₂: Bond order = (10 bonding electrons - 4 antibonding electrons) / 2 = 3.
What determines whether a molecule is paramagnetic or diamagnetic?
Paramagnetic: Molecule has unpaired electrons.
Diamagnetic: All electrons are paired.
How does effective nuclear charge influence molecular bonding?
Increased Z_eff strengthens the attraction between electrons and the nucleus, improving bond strength.
What type of bond is formed by the overlap of orbitals in a molecular orbital theory?
σ bonds: Formed by head-on overlap of orbitals.
π bonds: Formed by sidewise overlap of orbitals.
What is the key conclusion of Molecular Orbital Theory?
MOT explains bonding in molecules by considering the combination of atomic orbitals into molecular orbitals, leading to the formation of stable or unstable bonds based on electron distribution.
