Chapter 10: Molecular Structure and Bonding Theories Flashcards
the arrangement of the atoms in a molecule has a strong influence on its
physical properties and chemical reactivity
the valence-shell electron-pair repulsion (VSEPR) model predicts the shapes of most molecules from their
Lewis structures
the main premise of VSEPR model is that the electron pairs about an atom
repel each other
VSEPR Rule 1: a molecule hs a shape that …..
minimizes eletrostatic repulsions between valence-shell electron pairs
minimum repulsion results when the electron pairs are as
far apart as possible
the VSEPR model predicts the shape around
each central atom
steric number =
(number of lone pairs on central atom) + (number of atoms bonded to central atom)
the steric number is used to determine the
bonded-atom lone-pair arrangement
the BALPA is the shame that maximizes the distances between
regions of electron density about a central atom
bond angles for linear
180
bond angles for trigonal planar
120
bond angles for tetrahedral
109.5
bond angles for trigonal bipyramidal
90 and 120
bond angles for octahedral
90 and 90
SN: 2, balpa:
linear
SN: 3, BALPA:
trigonal planar
SN: 4, BALPA:
tetrahedral
SN: 5, BALPA:
trigonal bipyramidal
SN: 6, BALPA:
octahedral
two positions for molecular shapes:
axial and equatorial
axial atoms have different … from equatorial ones
environments
when central atoms have lone pairs, the molecular shape is not the same as the
bonded-atom lone-pair arrangement
the molecular shape is the geometric
arrangement of the atoms in a species
the lone pairs influence the molecular shape but are …, because there are no atoms at the …
not part of it; locations of the lone pairs
each type of electron pair exerts a different
repulsion on other electron pairs
VSEPR Rule 2: forces between electron pairs vary as
lone-pair-lone-pair repulsion>lone-pair-bonding-pair repulsion>bonding-pair-bonding-pair repulsion
in a trigonal bipyramidal BALPA, the structure that minimizes the number of 90 degree lone pair interactions is favored-
lone pairs always go to the equatorial position
for molecules with more than one central atom, the geometry about each atom is assigned by applying the VSEPR model to each
central atom individually
the VSEPR model does not predict how the geometry around one central atom will be oriented with respect to
others in the moleule
polar molecules will orient to maximie
electrostatic attractions
the degree of polarity is measured by a
dipole moment
the dipole moment is the magnitude of the separated charges times the
distance between them
the … between bonded atoms is used to predict the polarity of each bond, known as the …
difference in electronegativity; bond dipole
the dipole moment of the molecule is the
vector sum of the individual bond dipoles
molecules with lone pairs of electrons on a central atom generally are
polar
a molecule with polar bonds is nonpolar if its geometry causes the
bond polarities to sum to zero
molecules are nonpolar when there are no … on the central atom and all of the atoms bonded to the central atom are …
lone pairs; identical
valence bond theory describes covalent bonds as being fromed by atoms sharing valence electrons in
overlapping valence orbitals
(valence bond theory) the bonding is based on the … available to make bonds and the …. that the atoms provide for bonding
orbitals; number of valence electrons
hybrid orbitals are orbitals obtained by
mixing two or more atomic orbitals of the same central atom
the new hybrid orbitals have different … and … properties from the orbitals used in constructing them
shapes; directional
the energy and directional characteristics of the new hybrid orbitals are decided by the … and … of atomic orbitals used in the mixing
type; number
1 s orbital + 1 p orbital forms
two sp hybrid orbitals
the sp hybrid orbitals describe the bonding on central atoms that have
180 degree bond angles
the steric number of 2 indicates … hybrid orbitals
sp
1 s orbital + 2 p orbitals forms
3 sp^2 hybrid orbitals
for sp2 hybrid orbitals, … remains unchanged
one p orbital
the sp2 hybrid orbitals describe the bonding on atoms that have … and a steric number of ..
120 degree bond angles; 3
1 s orbital + 3 porbitals forms
4 sp^3 hybrid orbitals
the sp3 hybrid orbitals describe the bonding on central atoms that have approximately …. and a steric number of ..
109-degree bond angles; 4
for molecules that have central atoms with steric numbers of 5 or 6, more than … are needed to make the hybrid orbitals
four atomic orbitals
the additional orbitals are taken from the
d subshell
1 d orbital + 1 s orbital + 3 p orbitals forms
5 sp^3d hybrid orbitals
2 d orbitals + 1s orbital + 3 p orbitals
six sp^3d^2 hybrid orbitals
the steric number and number of hybrid orbitals are
equivalent
sigma bonds exist int he region
directly between two bonded atoms
in a sigma bond, the shared pair of electrons is symmetric about th eline
joining the two nuclei of the bonded atoms
all single bonds are
sigma bonds
sigma bonds form from the overlap of … orbitals or hybrid orbitals oriented …
s or p; along the bond
all hybrid orbitals make only
sigma bonds
pi bonds exist in the region … between two bonded atoms
above and below a line drawn
double bonds have .. sigma bond and … pi bond
1; 1
triple bonds have .. sigma bond and … pi bond
1; 2
isomers are compounds with the same … but different …
molecular formula; structures
when double bonds are formed between two carbon atoms, the potential for … isomerism arises due to lack of … around double bonds
cis-trans; rotation
cis-trans isomerism is observed only if each carbon atom has
2 different substitutents attached
pi bonds contribute to the … model of electrons in bonding, and help explain ..
delocalized; resonance
electron density from pi bonds can be distributed … all around the ring, above and below the plane
symmetrically
molecular orbital theory is a model that combines atomic orbitals to form new orbitals that are shared over the
entire molecule rather than between two atoms
a molecular orbital is a … of an electron in a molecule
wave function
the number of molecular orbitals formed must equal the number of
atomic orbitals used to make them
these wave functions can be added to generate … or they can be subtracted to generate …
bonding orbitals; anti-bonding orbitals
bonding orbitals concentrate electron density
between atoms
anti-bonding orbitals reduce the
electron density between atoms
bonding molecular orbitals are … and antibonding molecular orbitals are … than the atomic orbitals that are combined
more stable; less stable
moleuclar orbital theory allows us to calculate bond order (…) and the number of unpaired electrons (…)
measure of stability; paramagnetism
according to molecular orbital theory, bond order is :
1/2(# e- in bonding orbitals - #e- in anti-bonding orbitals)
a homonuclear diatomic molecule contains
two atoms of the same element
heteronuclear diatomic molecules contain one atom of each of
two different elements t
the molecular orbital diagrams are close to those for homonuclear diatomic molecules when the valence energies for each atom are
fairly close in energy
delocalized molecular orbitals are: orbitals in which an electron in a molecule is
spread over more than two atoms
cis: same substituents
parallel
trans: substitutents are
opposite to each other
