ES260 MATERIALS SCIENCE Prof' D' H' Rasmussen 218 CAMP x3820 rasmuclarkson'edu

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ES-260 MATERIALS SCIENCE Prof. D. H.
Rasmussen218 CAMP x3820rasmu_at_clarkson.edu 
   
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ELECTRONIC STRUCTURE OF ATOMS Bohr Theory --
Electrons (negative particles) travel in orbits
about a dense positively charged
nucleus. Quantum mechanics -- each electron
must exist in a unique energy state or orbit. On
transition from one energy state to another a
discrete amount of energy is emitted or absorbed.
 h 6.625 x 10-34 joule-secondc 3.00 x
108 meters/second  
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Pauli Exclusion Principle -- no two electrons
can have the same set of quantum numbers  
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TYPES OF ATOMIC AND MOLECULAR
BONDS Primary Atomic Bonds   Ionic
Bonds Covalent Bonds Metallic Bonds Secondary
Atomic Bonds  Permanent Dipole bonds - includes
hydrogen bonds Fluctuating Dipole Bonds - van
der Waal's forces  
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 IONIC BONDING Electron transfer from
electropositive metal atoms to electronegative
nonmetal atoms form ions which attract each other
by coulombic forces. 
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 Coulomb's Law of Attractionwhere Z1 and
Z2 electrons transferred in ion formatione
electronic chargea interionic separationeo
permittivity of free space eo 8.85 x 10-12
C2/(N-m2)
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Ion core repulsionwhere a interionic
separationb and n and (? and ?) are constants n
ranges from 7 to 9 n 9 for NaCl  
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Net force between two oppositely charged
ions      Interionic Energies equal the
integral of the net force from infinity to the
distance of separation, ao.The net potential is
then       
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Ion arrangement in Ionic Solids is determined
by 1. Ionic size ratio - Ionic bonds are not
directional and the maximum number of bonding
pairs (unlike ions) is determined by the ratio of
the radii of the ions. Geometry of arrangement
depends on number of nearest neighbors  2.
Electroneutrality - Ionic Solids are high melting
temperature insulators or semiconductors (charge
is carried by ion migration).
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COVALENT BONDING Electron pair sharing creates
bonds which establish noble gas structure for
each constituent atom.  Number of covalent
bonds depends on the atomic valence of the
pairing species. Strong bonds are created
between the atoms but not necessarily strong
bonds between molecules. Covalent bonding
creates useful solids when the bonding can
propagate in two or three dimensions (multiple
bonding functionality).
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Electron Sharing Hybridization quantum
mechanical interaction of the electronic wave
functions of the atoms such that s and p or s and
d atomic orbitals can combine to become
equivalent and permit a number of directional
covalent bonds between atom pairs. Examples
sp3, sp2, sp, sd5, etc Electrons in
covalent solids are localized to the covalent
bond.Covalent solids are insulators with high
melting points.
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METALLIC BONDING Positive ion cores of
metallic elements are bond together by a "sea" of
valence electrons. Structure is determined by
maximizing the number of nearest neighbors ion
cores and by lack of perfect "metallic bonding"
(i.e. a fraction of the bonding may be covalent
in character).Alkali metals are best examples.
They melt at a low temperature and are very
ductile (soft). They conduct both heat and
electricity because the electrons can move very
quickly across the block of metal and carry
charge and energy.
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 MIXED BONDING Possible types of primary mixed
bonding Ionic - covalentmetallic -
covalentmetallic - ionicionic - covalent -
metallic. Ionic - Covalent mixed bonding