Unit 12

Question 1

1st order valence electron MO correlation diagram

Answer 1

-on bonding orbital, two π are above one σ (π(px), π (py), and σ(pz))

Question 2

2 different correlation diagrams

Answer 2

-2nd order diagram (L2 - N2 and their ions)
-1st order diagrams (O2 - Ne2 and their ions)

Question 3

2nd order valence electron MO correlation diagram

Answer 3

-on bonding orbital, one σ is above two π (π(px), π (py), and σ(pz))

Question 4

MO energies across periodic table

Answer 4

-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

Question 5

paramagnetic

Answer 5

-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

Question 6

diamagnetic

Answer 6

-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

Question 7

p orbitals

Answer 7

-are dumbbell shaped, have a node between two oppositely charged lobes

Question 8

σ(pz)

Answer 8

-bonding
-nodes are vertical, lobes are horizontal
-two nodes, with large constructive molecular orbital in middle

Question 9

σ*(pz)

Answer 9

-antibonding
-nodes are vertical, lobes are horizontal
-three nodes, with small orbitals on either side of middle node

Question 10

π(px)

Answer 10

-bonding
-node is horizontal, lobes are vertical
-one node, with one bean shaped lobe on both sides of node

Question 11

π*(px)

Answer 11

-antibonding
-one node is horizontal, one is vertical
-two nodes, with four leaf shaped orbitals in each quadrant

Question 12

π(py)

Answer 12

-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)

Question 13

π*(py)

Answer 13

-antibonding
-one node is horizontal, one is vertical
-two nodes, with four leaf shaped orbitals in each quadrant (out of plane)

Question 14

HOMO

Answer 14

highest (energy) occupied molecular orbital

Question 15

LUMO

Answer 15

lowest (energy) unoccupied molecular orbital

Question 16

Types of bonds

Answer 16

-non-polar covalent (homonuclear)
-polar covalent
-ionic

Question 17

Non-polar covalent bond

Answer 17

-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)

Question 18

Polar covalent bond

Answer 18

-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)

Question 19

Ionic bond

Answer 19

-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

Question 20

2nd Row Heteronuclear Diatomics

Answer 20

-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

Question 21

LCAO (Linear combination of atomic orbitals)

Answer 21

-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

Question 22

Combining LEM and MOT

Answer 22

-LEM is used to describe localized electrons via σ framework
-MOT is used to describe delocalized electrons via π framework

Question 23

Localized electrons

Answer 23

electrons that are attached to a constant atom and do not change between resonance structures

Question 24

Delocalized electrons

Answer 24

electrons that are not attached to a constant atom and change positions between different resonance structures

Question 25

Bond Order (BO) in combined MOT/LEM

Answer 25

[1/2(bonding-antibonding)]/(# of eq bonds)

Question 26

Polygon Rule (Frost Circle)

Answer 26

-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

Question 27

π framework delocalized electron MO rules

Answer 27

-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

Question 28

non-bonding MO

Answer 28

-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

Question 29

Drawing LEM/MOT and positioning nodes in π framework

Answer 29

-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

Question 30

π framework for heteronuclear atoms

Answer 30

-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

Question 31

bonding vs antibonding interactions in π framework

Answer 31

-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