Chapter 10 Flashcards
molecular geometry
the general shape of a molecule, as determined by the relative positions of the atomic nuclei
Valence-Shell Electron Pair Repulsion (VSEPR) Model
the VSEPR model predicts the shapes of molecules and ions by assuming that the valence-shell electron pairs (bonding and non-bonding) are arranged about each atom so that electron pairs are kept as far away from one another as possible, thereby minimizing electron pair repulsion
A common feature of both trigonal planar
and tetrahedral VSEPR geometries is that
each site is equivalent and so there is
only one possibility of locating lone pairs
Because a lone pair tends to require more space than a bonding
pair, it tends to
reduce the bond angles.
A trigonal bipyramidal geometry has two distinct sites:
axial and equatorial.
Dipole Moment:
A quantitative measure of the degree of charge
separation in a molecule
dipole moment of polar bonds
A polar bond is characterized by separation of electrical charge.
Polar molecules, therefore, have nonzero dipole moments.
SI unit for the dipole moment is the
coulomb•meter, also known as the
Debye (D).
Polarity and Boiling Point
The attractive forces due to the polarity increases the amount of energy required for
the liquid to boil.
is VSEPR theory always right?
no lol
what provides a more accurate means of determining molecular structures?
molecular orbital theory
a covalent bond forms when …
• An orbital on one atom comes to occupy a portion of
the same region of space of an orbital on the other
atom. The two orbitals are said to overlap.
• The total number of electrons in both orbitals is no
more than two.
• The greater the orbital overlap, the stronger the bond.
Valence-bond theory
gives us the first description of covalent bonding in
terms of atomic orbitals (a quantum mechanical method).
Hybridization
Hybrid orbitals are formed when two or more atomic
orbitals on the same atom are mixed to form a new set of hybrid
orbitals.
The number of hybrid orbitals is equal to the number of
pure
atomic orbitals used in the hybridization process
Covalent bonds are formed by:
a. Overlap of hybrid orbitals with atomic orbitals.
b. Overlap of hybrid orbitals with other hybrid orbitals.
How Do I Predict the Hybridization of the Central Atom
Count the number of lone pairs AND the number of atoms
bonded to the central atom
Orbital Diagrams and Valence Bond Theory: Valence bond theory allows us to explain this in two steps:
promotion and hybridization
What happens during multiple bonding?
When more than one orbital from each bonding atom overlaps, a multiple
bond is formed.
σ bond (sigma)
has a cylindrical shape about the bond axis. It is formed either when two s orbitals overlap or with directional orbitals (p or hybrid), when they overlap along their axis.
π bond (pi)
has an electron distribution above and below the bond axis.
It is formed by the sideways overlap of two parallel p orbitals.
This overlap occurs when two parallel half-filled p orbitals are
available after σ bonds have formed.
Bond Orders
A single bond is σ-bond
A double bond is a σ-bond plus a π-bond
A triple bond is a σ-bond plus two π-bonds
molecular orbital theory does not
constrain
the electrons to being localized between pairs of atoms, but
allows the electrons to occupy orbitals that are spread over the
entire molecule
molecular orbitals are
mathematical functions
that can be used to indicate the probability of finding an electron at
a given position.
Also like an atomic orbital, a molecular orbital can only
accommodate a maximum of
two electrons, in which case they
must have opposite spin.
Molecular orbital theory definition
Bonds are formed from the interaction of atomic orbitals to form
molecular orbitals
As two atoms approach each other, the orbitals overlap and interfere either
constructively (addition) or destructively (subtraction).
bonding orbital
addition of orbitals builds up electron density in overlap region
antibonding orbital
subtraction of orbitals results in low electron density in the overlap region
An antibonding molecular orbital has
higher energy and lower stability than the
atomic orbitals from which it was formed.
A bonding molecular orbital has
lower
energy and greater stability than the atomic
orbitals from which it was formed.
Bond order:
the number of bonds that exist between two atoms can be
calculated using the equation:
A bond order of zero means
a bond is not formed!
Delocalization
is central feature of molecular orbital theory where rather than the lone pair of electrons contained in localize bonds (as in the valence bond theory), electrons can exist in molecular orbitals that are spread over the entire molecule
