Unit 12 Flashcards
1st order valence electron MO correlation diagram
-on bonding orbital, two π are above one σ (π(px), π (py), and σ(pz))
2 different correlation diagrams
-2nd order diagram (L2 - N2 and their ions)
-1st order diagrams (O2 - Ne2 and their ions)
2nd order valence electron MO correlation diagram
-on bonding orbital, one σ is above two π (π(px), π (py), and σ(pz))
MO energies across periodic table
-MO energies decrease left-right due to higher Z*
-higher Z* (for 1st order elements) results in different ordering of molecular orbitals, so σ(pz) is lower in energy than π(px) and π (py) MOs
paramagnetic
-an atom/ion that is attracted into a magnetic field
-attributed to the presence of one or more unpaired electrons
-total spin ≠ 0
-ex.) O2, B2
diamagnetic
-an atom/ion that is pushed out of a magnetic field
-can be attributed to all electrons being paired
-total spin = 0
-ex. H2, Li2, N2, F2
p orbitals
-are dumbbell shaped, have a node between two oppositely charged lobes
σ(pz)
-bonding
-nodes are vertical, lobes are horizontal
-two nodes, with large constructive molecular orbital in middle
σ*(pz)
-antibonding
-nodes are vertical, lobes are horizontal
-three nodes, with small orbitals on either side of middle node
π(px)
-bonding
-node is horizontal, lobes are vertical
-one node, with one bean shaped lobe on both sides of node
π*(px)
-antibonding
-one node is horizontal, one is vertical
-two nodes, with four leaf shaped orbitals in each quadrant
π(py)
-bonding
-node is horizontal, lobes are horizontal (out of plane)
–one node, with one bean shaped lobe on both sides of node (out of plane)
π*(py)
-antibonding
-one node is horizontal, one is vertical
-two nodes, with four leaf shaped orbitals in each quadrant (out of plane)
HOMO
highest (energy) occupied molecular orbital
LUMO
lowest (energy) unoccupied molecular orbital
Types of bonds
-non-polar covalent (homonuclear)
-polar covalent
-ionic
Non-polar covalent bond
-a bond in which each atom of a bound pair contributes one electron to form a pair of electrons (electron pair bond)
-forms between two identical atoms (A and A)
-difference in electronegativity=0
-symmetric electron density (each atom “pulls” equally on bonding electrons and there is equal distribution of electron density between atoms)
Polar covalent bond
-bond formed by sharing of electrons between two different atoms (A and B)
-difference in electronegativity < 2
-unequal sharing of electrons
-bonds found in molecules
-asymmetric electron density (more electronegative atom pulls on electrons more, thereby receiving larger distribution of electron density, A feels less repulsive force)
Ionic bond
-bond between 2 unlike atoms (A and B) where an electron is taken completely away from one atom and transferred to partner
-difference in electronegativity > 3
-more electronegative atom receives all of electron density, while other receives none
2nd Row Heteronuclear Diatomics
-more electronegative atom will contribute more to bonding (lower in energy) orbital (σ)
-less electronegative atom will contribute more to antibonding (higher in energy) orbital (σ*)
-polarized towards the atom with the atomic orbital closest in energy (lower in energy)
-orbital will be larger for more electronegative atom in bonding (more amplitude)
-orbital will be larger for less electronegative atom in antibonding (more amplitude)
-Atomic orbitals that are far from a specific molecular orbital tend to not contribute to that orbital
LCAO (Linear combination of atomic orbitals)
-method for approximating molecular orbitals/wavefunctions
-probability density of finding election in molecular orbital = square of each MO
-approximates MOs by taking linear combinations of atomic orbitals
Combining LEM and MOT
-LEM is used to describe localized electrons via σ framework
-MOT is used to describe delocalized electrons via π framework
Localized electrons
electrons that are attached to a constant atom and do not change between resonance structures
Delocalized electrons
electrons that are not attached to a constant atom and change positions between different resonance structures
Bond Order (BO) in combined MOT/LEM
[1/2(bonding-antibonding)]/(# of eq bonds)
Polygon Rule (Frost Circle)
-MO energy levels scale with the positions of the vertices of the polygon with 1 vertex pointing down
-used when there are delocalized electrons present
π framework delocalized electron MO rules
-for linear molecules (C4H6), an even number of p atomic orbitals participating in delocalization of π electrons results in an equal number of bonding and anti-bonding MOs, with zero non-bonding MOs
-an odd number of p orbitals participating in delocalization of π electrons results in an equal number of bonding and antibonding MOs plus one non-bonding MO
non-bonding MO
-a molecular orbital whose occupation by electrons neither increases nor decreases the bond order between the involved atoms
-neither bonding nor antibonding orbitals, and often correspond to lone pairs on an atom in a molecule
Drawing LEM/MOT and positioning nodes in π framework
-Draw nodes perpendicular to the plane of the atoms in molecule
-arrange nodes as symmetrically as possible (similar to PIB)
-planar nodes should be placed either between two atoms or such that the plane contains the atom’s nucleus
-amplitude sign should change when crossing node
π framework for heteronuclear atoms
-lobes should be drawn larger for more electronegative atoms in bonding π MOs
-lobes should be drawn larger for less electronegative atoms in antibonding π MOs
bonding vs antibonding interactions in π framework
-bonding: no planar node, atoms are adjacent and same sign
-antibonding: planar node seperates lobes, adjacent are different signs
-Bonding= more bonding than antibonding
-Antibonding= more antibonding than bonding
