ACS STUDY GUIDE EXAM QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS VERIFIED | 2026/2027 LATEST UPDATE |
GRADED A+
Zeff increases - ANSWER across the periodic table left to right
Ionization energy increases - ANSWER left to right across a row and up column of the periodic table
Electron affinity increases - ANSWER left to right across a row and up a column of the periodic table
Element size increases - ANSWER right to left across and row and down a column of the periodic
table
Ionization energy - ANSWER the energy required to remove an electron from an atom
Electron affinity - ANSWER the energy required to add an electron to an atom
In M.O. theory, the number of atomic orbitals must equal... - ANSWER the number of molecular
orbitals
M.O. requirements - ANSWER 1. M.O.s must be built from symmetrically appropriate orbitals
2. Energy in bond pairs needs to be approximately the same
3. Efficient overlap of orbitals in a bond
Anti bonding orbitals - ANSWER higher in energy than bonding orbitals, created by overlap of orbitals
that are out of phase with each other, contain nodes
Node - ANSWER a region with no electron density
Bond order - ANSWER b=0.5(# bonding electrons - # anti-bonding electrons)
tells you how many bonds to expect in a molecule
, M.O.s for B2, C2, and N2 - ANSWER there is a small change in energy between 2s and 2p orbitals,
causing them to mix
this results in the 3 sigma orbital to be higher in energy than the 1 pi orbital
Heteronuclear M.O. theory - ANSWER the more electronegative atom is lower in energy
Non-bonding orbitals - ANSWER essentially lone pairs, caused when the overlap between orbitals is
not enough
CO M.O. diagram - ANSWER reaction takes place at carbon because the frontier orbital is mainly
"carbon-like" in character
the 3 sigma orbital switches places with the 1 pi orbital
"X-like character" in M.O. - ANSWER an orbital has "x-like character" when it is much closer in energy
to one atom rather than the other
Symmetry element - ANSWER a point or an axis that a symmetry operation exits, such as a rotation,
mirror plane, inversion, etc.
Symmetry operation - ANSWER perform a transformation that leaves the "new" version of the
molecule identical to the original
Rotation, Cn - ANSWER rotation=360/n
Identity, E - ANSWER if you spin a molecule 360 degrees, you'll end up with exactly what you started
with, every molecule has this symmetry operation
Mirror plane, sigma h - ANSWER reflecting a molecule through a plane of symmetry
Inversion center, i - ANSWER reflects all points of a molecule through the center
Improper rotation, Sn - ANSWER 1. rotate by 360/n
2. reflect through a perpendicular mirror plane
COMPLETE SOLUTIONS VERIFIED | 2026/2027 LATEST UPDATE |
GRADED A+
Zeff increases - ANSWER across the periodic table left to right
Ionization energy increases - ANSWER left to right across a row and up column of the periodic table
Electron affinity increases - ANSWER left to right across a row and up a column of the periodic table
Element size increases - ANSWER right to left across and row and down a column of the periodic
table
Ionization energy - ANSWER the energy required to remove an electron from an atom
Electron affinity - ANSWER the energy required to add an electron to an atom
In M.O. theory, the number of atomic orbitals must equal... - ANSWER the number of molecular
orbitals
M.O. requirements - ANSWER 1. M.O.s must be built from symmetrically appropriate orbitals
2. Energy in bond pairs needs to be approximately the same
3. Efficient overlap of orbitals in a bond
Anti bonding orbitals - ANSWER higher in energy than bonding orbitals, created by overlap of orbitals
that are out of phase with each other, contain nodes
Node - ANSWER a region with no electron density
Bond order - ANSWER b=0.5(# bonding electrons - # anti-bonding electrons)
tells you how many bonds to expect in a molecule
, M.O.s for B2, C2, and N2 - ANSWER there is a small change in energy between 2s and 2p orbitals,
causing them to mix
this results in the 3 sigma orbital to be higher in energy than the 1 pi orbital
Heteronuclear M.O. theory - ANSWER the more electronegative atom is lower in energy
Non-bonding orbitals - ANSWER essentially lone pairs, caused when the overlap between orbitals is
not enough
CO M.O. diagram - ANSWER reaction takes place at carbon because the frontier orbital is mainly
"carbon-like" in character
the 3 sigma orbital switches places with the 1 pi orbital
"X-like character" in M.O. - ANSWER an orbital has "x-like character" when it is much closer in energy
to one atom rather than the other
Symmetry element - ANSWER a point or an axis that a symmetry operation exits, such as a rotation,
mirror plane, inversion, etc.
Symmetry operation - ANSWER perform a transformation that leaves the "new" version of the
molecule identical to the original
Rotation, Cn - ANSWER rotation=360/n
Identity, E - ANSWER if you spin a molecule 360 degrees, you'll end up with exactly what you started
with, every molecule has this symmetry operation
Mirror plane, sigma h - ANSWER reflecting a molecule through a plane of symmetry
Inversion center, i - ANSWER reflects all points of a molecule through the center
Improper rotation, Sn - ANSWER 1. rotate by 360/n
2. reflect through a perpendicular mirror plane
