Chapter 11: Chemical Bonding II: Molecular Shapes, Valence Bond Theory, and Molecular Orbital Theory Flashcards
Properties of molecular substances depend on what?
the structure of the molecule
what does the structure include?
The skeletal arrangement of the atoms
type of bonding between the atoms
The shape
allow us to predict the shapes of molecules
the bonding theories
have characteristic “corners” that indicate the positions of the surrounding atoms around a central atom in the center of the geometric figure.
geometric figures
The geometric figures also have characteristic angles that we call
bond angles
predicts there are distinct regions in an atom containing bonding and nonbonding electrons
Lewis
distinct regions in an atom containing bonding and nonbonding electrons
electron groups
repel each other as they are regions of negative charge
electron groups
what charges are electron groups
negative
can be used to predict the shapes of the molecules.
The repulsion of electron groups in Lewis structures
The position of atoms surrounding a central atom will be determined by what?
the location of the bonding electron groups.
are positioned to minimize repulsive forces.
the electron groups
what is the VSEPR theory
Electron groups around the central atom will be most stable when they are as far apart as possible.
what constitutes as a electron group on a central atom
Each lone pair of electrons
and
Each bond regardless of whether it is single, double, or triple
For molecules with a single central atom that exhibit what the electron geometry is the same for all structures
resonance
When there are two electron groups around the central atom, This results in the electron groups taking a
linear electron geometry.
What shape will this molecule make
Linear electron geometry
what is the bond angle for linear electron geometry.
180 degrees
When there are three electron groups around the central atom, This results in the electron groups taking a
trigonal planar electron geometry
What Shape will this molecule make?
Trigonal planar electron geometry
what bond angle is trigonal planar electron geometry
120 degrees
When there are four electron groups around the central atom, This results in the electron groups taking a
tetrahedral electron geometry.
What shape does this molecule take
Tetrahedral electron geometry
what is the bond angle for tetrahedral electron geometry.
109.5°
When there are five electron groups around the central atom, This results in the electron groups taking a
Trigonal Bipyramidal Electron Geometry
What shape does this molecule take
Trigonal Bipyramidal electron geometry
what are the two positions in Trigonal Bipyramidal Electron Geometry
axial
and
equatorial
what is the bond angle for equatorial positions
120 degrees
The bond angle between axial and equatorial positions is what?
90 degrees
The positions above and below the central atom are called the
axial positions
What shape does this molecule take
Ortahedral geometry
The positions in the same base plane as the central atom are called the
equatorial positions
When there are four electron groups around the central atom, This results in the electron groups taking a
Octahedral Electron Geometry
The actual geometry of the molecule is called its
molecular geometry
what affects molecular geometry?
groups attached to atoms of diff sizes and
binding to one atom is different form other atom
Lone pairs
“occupy more space” on the central atom because their electron density is exclusively on the central atom, rather than shared like bonding electron groups.
Lone pairs
Relative sizes of repulsive force interactions is as follows:
Lone Pair – Lone Pair > Lone Pair – Bonding Pair > Bonding Pair – Bonding Pair
The bonding electrons are shared by two atoms, so some of the what is removed from the central atom.
negative charge
The nonbonding electrons are localized on the central atom, so the area of negative charge what?
takes more space
When there are four electron groups around the central atom, and one is a lone pair, the result is called a
trigonal pyramidal molecular geometry,
What is this?
Trigonal pyramidal molecular geometry
what are the bond angles of trigonal pyramidal molecular geometry,
107 degrees
When there are four electron groups around the central atom, and two are lone pairs, the result is called a
tetrahedral–bent molecular geometry.
What is this
Tetrahedral-bent molecular geometry
what are the bond angles of tetrahedral–bent molecular geometry.
104.5
When there are three electron groups around the central atom, and one of them is a lone pair, the resulting shape of the molecule is called a
trigonal planar–bent molecular geometry.
What is this
Trigonal planar-bent molecular geometry
what is the bond angle of trigonal planar–bent molecular geometry?
less than 120°
What is this?
Seesaw shape or distorted tetrahedron
When there are five electron groups around the central atom, and one is a lone pair, the result is called the
seesaw shape (aka distorted tetrahedron).
What is this
T-shaped
When there are five electron groups around the central atom, and two are lone pairs, the result is
T-shaped.
What is this
Square Pyramidal Shape
When there are six electron groups around the central atom, and one is a lone pair, the result is called a
square pyramid shape
What is this
Square planar shape
When there are six electron groups around the central atom, and two are lone pairs, the result is called a what
square planar shape.
indicate bonds on the same plane with what?
straight line
For atoms in front of the plane, use a
solid wedge
For atoms behind the plane, use a
hashed wedge.
The bonding electrons are pulled equally toward both O ends of the molecule. The net result is a what?
nonpolar molecule
polarity depends on what?
the shape of the molecule
Both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a what?
polar molecule.
affects the intermolecular forces of
attraction.
polarity
which shapes are polar?
bent
and
trigonal pyramidal
which shapes are non polar?
linear
trigonal planar
tetrahedral
polar molecules are attracted to what?
other polar molecules
do ionic compounds dissolve in water?
yes
problems with the lewis model
- does not give good numerical predictions.
- cannot be used to get the actual angle.
- Cannot write one correct structure for many molecules where resonance is important.
- Often does not predict the correct magnetic behavior of molecules.
The electron density of the valence electrons is localized between the bonding atoms.
Valence Bond (VB) Theory
The valence electrons, located in half-filled atomic orbitals (s, p, d, and f), overlap to form molecular bonds.
Valence Bond (VB) Theory
The electron density of the valence electrons is delocalized within the molecule.
Molecular Orbital (MO) Theory
The valence electrons occupy molecular orbitals that spread throughout the entire molecule.
Molecular Orbital (MO) Theory
When orbitals on atoms interact constructively, they make a bond.
valence bond theory
If the energy of the system is lowered because of these interactions, a what forms?
chemical bond
a chemical bond results from what according to the VB theory
from the overlap of two half- filled orbitals with spin-pairing of the two valence electrons
or
the overlap of a completely filled orbital with an empty orbital.
what determines the shape of the molecule?
The geometry of the overlapping orbitals
As two atoms approach each other, the half-filled valence atomic orbitals on each atom would interact to form
molecular orbitals
are regions of high probability of finding the shared electrons in the molecule.
molecular orbitals
The potential energy is lowered when?
the molecular orbitals contain a total of two paired electrons compared to separate, one-electron atomic orbitals.
issues with the VB theory
does not predict the number of bonds or orientation of bonds.
apparently, valence atomic orbital what before binding takes place
hybridize
producing four hybrid orbitals that point at the corners of a tetrahedron.
hybridze
involves the mixing of different types of orbitals in the valence shell to make a new set of degenerate orbitals.
Hybridization
what determines the shape of a hybrid orbital?
The number and type of standard atomic orbitals
The particular kind of hybridization that occurs is the one that what?
yields the lowest overall energy for the molecule
For hybridization what are central atoms with four electron groups
sp3 hybridized
what geometry does sp3 hybridized have?
Tetrahedral geometry
On-axis overlap of atomic orbitals produce what?
sigma bonds
Unhybridized p orbital can overlap adjacent to the internuclear axis with the unhybridized p orbital of another atom forming a
pi bond.
where are sigma bonds usually seen
Either standard atomic orbitals or hybrids
s to s, p to p, hybrid to hybrid, s to hybrid, etc.
results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei.
pi bond
which is stronger pi bonds or sigma bonds
sigma bonds
“Overlap” between a hybrid orbital on one atom with a hybrid or non-hybridized orbital on another atom results in a what?
sigma bond
“Overlap” between unhybridized p orbitals on bonded atoms results in a what?
pi bond
rotation around what bond does not require breaking the interaction between the orbitals
sigma
rotation around what bond does require breaking the interaction between the orbitals
pi
which hybridization is four electron groups?
sp^3 hybridization
which hybridization is three electron groups?
sp^2
which geometry does sp^2 have?
trigonal planar system
which hybridization is two electron groups?
sp hybridization
what shape is sp hybridization?
linear
which hybridization is five electron groups?
sp^3d
what shapes are the sp^3d?
-Trigonal bipyramid
-Seesaw
-T–shape
-Linear
which hybridization is six electron groups?
sp^3d^2
what shapes are the sp^3d^2?
- Octahedral electron
-Square pyramid
-Square planar
limitations of the VB theory are
-doesn’t describe magnetic behavior of O2
-doesn’t account for delocaliztion
in this theory we apply Schrödinger’s wave equation to the molecule to calculate a set of molecular orbitals.
Molecular Orbital (MO) Theory
what is special ab the Molecular Orbital (MO) Theory
the electrons and orbital belong to the whole molecule
The simplest mathematical solution is the summation of the atomic orbitals of the atoms to form molecular orbitals; this summation is called the
linear combination of atomic orbitals (LCAO)
Because the orbitals are wave functions, the waves can combine either what or what?
constructively or destructively.
this wave function results in a molecular orbital that has less energy than the original atomic orbitals
constructively
what is a constructively wave called
bonding molecular orbital.
where can most of the electron density be found in binding (MO)
between the nuclei
this wave function results in a molecular orbital that has more energy than the original atomic orbitals
destructively
where can most of the electron density be found in antibinding (MO)
outside the internuclear axis
which has more energy electron in bonding MO or atomic orbitals
atomic orbitals
which has more energy electron in antibonding MO or atomic orbitals
antibonding MO
Electrons in antibonding orbitals what stability gained by electrons in bonding orbitals.
cancel
if there are unpaired electrons what is the substance?
paramagnetic
if there are no unpaired electrons what is the substance?
diamagnetic
When the combining atomic orbitals
are of different types and energies, which orbital contributes more to the molecular orbital.
the atomic orbital closest in energy to the molecular orbital
When many atoms are combined together, the atomic orbitals of all the atoms are combined to make a set of molecular orbitals, which are
delocalized over the entire molecule.
