Level 50 Level 52
Level 51

Molecular Shapes, Valence Bond Theory


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VSEPR
(valence shell electron pair repulsion);
electron groups
general term for lone pairs, single bonds, multiple bonds, or lone electrons in a molecule
maximum
the preferred geometry of a molecule is the one in which the electron groups have the _______ separation (and therefore the minimum energy) possible
one central atom
molecules with _______ => molecular geometry depends on
linear geometry
molecular geometry of three atoms with a 180 degree bond angle due to the repulsion of two electron groups
trigonal planar geometry
3 electron groups maximize separation by assuming 120° bond angles in a plane
tetrahedral geometry
109.5° angles between the electron groups
equatorial positions
those located along the same plane but are separated from each other by angles other than 180 degrees
axial positions
The elements on the outside that run in a straight line through the central atom to obtain the axial positions in the electron structure
octahedral geometry
six electron groups around a central atom assume an _______, eight-sided shape given
electron geometry
geometrical arrangement of electron groups in a molecule
molecular geometry
geometrical arrangement of atoms in a molecule
lone pair
a _______ (or non bonding electron air) occupies more apace than a bonding pair
trigonal pyramidal
4 electron groups with lone pair
most repulsive
lone pair-lone pair
least repulsive
bonding pair-bonding pair (no lone pairs)
repulsivity
most repulsive -> least repulsive
standard atomic orbitals
s,p,d, and f <--learned these in chapter 7
hybridized atomic orbitals
a kind of blend or combination of 2+ standard orbitals
Valence bond theory
A covalent bond forms when orbitals of two atoms overlap and a pair of electrons occupy the overlap region
chemical bond formed
if the energy of the system is lowered because of interactions between atoms' e-s and nuclei
interaction energy
usually calculated as a function of the internuclear distance between the two bonding atoms
Chemical Bond
An attractive force that holds together the atoms, ions, or groups of atoms in a molecule or compound.
shape of a molecule
determined by geometry of the overlapping orbitals
covalent chemical bond
i.e. 2 half filled orbitals overlap, occupy same space
Lewis theory
in this theory - a covalent chemical bond is the sharing of electrons (represented by dots)
hybridization
a mathematical procedure in which the standard atomic orbitals are combined to form new atomic orbitals called hybrid orbitals that correspond more closely to the actual distribution of electrons in chemically bonded atoms
hybrid orbitals
_______ are eqivalent because they have the same size, shape, and energy
hybridize
generally - the more bonds that an atom forms, the greater the tendency of its orbitals to _______
number
the _______ of standard atomic orbitals added together always equals the _______ of hybrid orbitals formed
PARTICULAR COMBINATIONS
the _______ of standard atomic orbitals added together determines the SHAPES AND ENERGIES of the hybrid orbitals formed
lowest
compounds form to achieve the _______ possible energy
sp3 hybridization
one s orbital and three p orbitals combine to form four sp3 hybrid orbitals
sp2 hybridization
one s orbital and 2 p orbitals results in 3 sp2 hybrids and 1 leftover unhybridized p orbital
p bond
when p orbitals overlap side by side and the electron density is above and below the internuclear axis
s bond
when orbitals overlap end to end
Single bond
1 pair of shared electrons
double bond
2 atoms share 4 electrons (2 pairs)
triple bond
2 atoms share 6 electrons (3 pair)
weaker
intermolecular forces are _ than bonds
unrestricted
rotation about a single bond is relatively _______
restricted
rotation about a double bond is highly _______
sp hybridization
one s and one p orbital combine to form 2 sp hybrid orbitals nad 2 leftover unhybridized p orbitals
sp hybrid orbitals
give two orbitals with a bond angle of 180° (linear geometry)
sp3d hybridization
hybridization of
sp3d2 hybridization
hybridization of
third period
these elements in the _______, can exhibit expanded octets
3d orbitals
for 3rd period elements, these orbitals become involved in hybridization because their energies are close to the energies of the 3s and 3p orbitals
molecular orbital theory
(MO) - dont solve Schrödinger equation for a molecule directly, Instead you use a trial function, an "educated guess" as to what the solution might be
LCAO
linear combinations of atomic orbitals
Mixing
? Rules for _______