Molecular Orbital Theory and VSEPR Flashcards
(30 cards)
What is a molecular orbital
A molecular orbital is a particular spatial distribution of electrons in a molecule that is associated with a particular orbital energy. They are not localized on a single atom but extend over the entire molecule, so allow a delocalised picture of bonding.
How can molecular orbitals be formed by the interaction of atomic orbitals
Molecular orbitals are formed by the overlap of atomic orbitals, which can be in phase (bonding) or out of phase (anti-bonding). N atomic orbitals will combine to give N molecular orbitals. Molecular orbitals can also be non-bonding. In order to calculate the molecular orbital wavefunction, a linear combination of atomic orbitals is used as an approximation. There are three types of overlap of atomic orbitals which leads to the formation of molecular orbitals - sigma, pi, and delta.
How can molecular orbitals be used to explain the formation of chemical bonds
Calculation of bond order = 1/2 (bonding - antibonding). This is indicative of the stabilising effect of filling bonding molecular orbitals and the destabilising effect of filling those which are antibonding.
What is a point group in molecular symmetry?
A point group is a set of symmetry operations that leave at least one point in the molecule unchanged.
True or False: The point group of a molecule can change depending on its conformation.
True
Which point group describes a molecule with a single axis of rotation and no other symmetry elements?
C1
What point group is assigned to molecules with a vertical mirror plane and a two-fold rotation axis?
C2v
Fill in the blank: A molecule with three-fold rotational symmetry and no mirror planes belongs to the point group _______.
C3
What is the point group for a tetrahedral molecule like methane (CH4)?
Td
Which point group is characterized by having a center of inversion?
Ci
True or False: A linear molecule with a center of inversion belongs to the D∞h point group.
True
What point group does a molecule with four identical ligands in a square planar arrangement belong to?
D4h
Identify the point group of ammonia (NH3).
C3v
What is the defining characteristic of the Dnh point groups?
They have n-fold rotational symmetry and horizontal mirror planes.
Which point group includes a molecule with a horizontal mirror plane and a two-fold rotation axis?
C2h
True or False: All molecules with no symmetry elements belong to the point group C1.
True
What is the point group for a molecule that has a three-fold axis and three vertical mirror planes?
D3h
Fill in the blank: The point group of benzene (C6H6) is _______.
D6h
Which point group is assigned to a molecule that possesses only a center of inversion?
Ci
Identify the point group of a molecule with a dihedral symmetry and four equivalent ligands.
D4
What is the point group for a molecule with a four-fold rotation axis and two vertical mirror planes?
D4h
True or False: A molecule that exhibits both rotational and reflectional symmetry is likely to belong to a higher symmetry point group.
True
What point group describes a molecule with only a two-fold rotation axis and no mirror planes?
C2
Fill in the blank: A molecule with two-fold rotational symmetry and a horizontal mirror plane belongs to the point group _______.
C2h
