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Level 53

Orbital Hybridization & Molecular Orbitals


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valence bond (VB) theory
developed largely by Linus Pauling; closely tied to Lewis's idea of bonding electron pairs between atoms & lone pairs of electrons localized on a particular atom; method of choice to provide qualitative, visual pictur…
molecular orbital (MO) theory
a more sophisticated model of bonding that can be applied equally successfully to simple and complex molecules
overlap
interpenetration; increases probability of finding electrons in region of space btwn 2 nuclei; the idea that bonds are formed by _______ of orbitals is the basis for valence bond theory
sigma bond
a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei
orbital hybridization
theory proposed by Linus Pauling to describe the bonding in methane & other molecules; new set of orbitals could be created by mixing s, p, and/or d atomic orbitals on atom
hybrid orbitals
_______ are eqivalent because they have the same size, shape, and energy
trigonal-planar electron-pair geometry
requires central atom w/ 3 hybrid orbitals in plane, 120 degrees apart
3 hybrid sp^2 orbitals
will lie in x-y plane if px & py are orbitals used in hybrid orbital formation
linear electron-pair geometry
describes a central atom in a molecule in which 2 hybrid orbitals, 180 degrees apart, are present
2 hybrid sp orbitals
formed when 1s & 1p are hybridized; if the px orbital is used, then the sp orbitals are oriented along the x-axis; the py & pz orbitals are perpendicular to this axis
sigma bonds
s bonds; arise from overlap of atomic orbitals so that the bonding electrons lie along the bond axis
pi bond
A bond formed when parallel p orbitals overlap creating two regions of electron density, one above and one below the internuclear axis.
isomers
compounds that have same formula but different structures
Molecular Orbitals
an orbital resulting from an overlapping of atomic orbitals when two atoms combine
first principle of molecular orbital theory
states that total # of molecular orbitals produced always equal to total # of aomic orbitals contributed by atoms that have combined
bonding molecular orbital
molecular orbital lower in energy than parent orbitals
antibonding molecular orbital
molecular orbital constructed by subtracting 1 atomic orbital from other; probability of finding electron between nuclei in molecular orbital reduced & probability of finding electron between nuclei in molecular orbital reduced & probability of fin…
second principle of molecular orbital theory
bonding molecular orbital lower in energy than parent orbitals & antibonding orbital is higher in energy; energy of group of atoms is lower than the energy of separated atoms when electrons are assigned to bon…
third principle of molecular orbital theory
electrons of molecule are assigned to orbitals of successively higher energy according to Pauli exclusion principle & Hund's rule; analogous to procedure for building up electronic structures of atoms; electrons occupy lowest energy orbitals avail…
fourth principle of molecular orbital theory
atomic orbitals combine to form molecular orbitals most effectively when the atomic orbitals are of similar energy
homonuclear diatomic molecule
molecule formed from 2 identical atoms
band theory
in metal, molecular orbitals spread out over many atoms & blend into band of molecular orbitals - energies of which are closely spac…
Fermi level
highest filled level @ 0 K
valence band
highest occupied band; in a metal, it is only partially filled
conduction band
higher-energy unfilled band of antibonding orbitals
band gap
energy difference separating 2 bands
intrinsic semiconductors
# of electrons in conduction band entirely governed by temp & magnitude of band gap; smaller band gap, smaller energy required to promote significant # of electrons; as temperature increases, larger # of electrons…
extrinsic semiconductor
conductivity of these materials is controlled by adding small #s of atoms of different kinds of impurities called dopants