Primary

1
Chemical Bonding

• Primary
• Ionic
• Electronegative/Electropositive
• Metallic
• Electropositive give up electrons
• Colavent
• Electronegative want electrons
• Shared electrons along bond direction
• Secondary
• Fluctuating/instantaneous dipoles
• Permanent dipoles (H-bonds)

Isotropic, filled outer shells
2
Covalent Bonds

• Locally well-defined orbitals
• Example carbon (C)
• 6 electrons 1s22s22p2
• filled octet rule 8-N (n) electrons to share
• 2s22p2 ? N 4 ? n 4

s orbital
p orbitals
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• solution sp2 or sp3 hybrization

http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
orbitals.gif
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Hybridized Bonds

• Elemental carbon (no other elements)

sp3 hybridization
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?
?
?
also methane CH4
one s three p orbitals ? 4 electron states (all
four orbitals overlaid)
4
Hybridized Bonds

• Elemental carbon (no other elements)

sp2 hybridization
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?
?
?
trigonal symmetry
one s two p orbitals ? 3 electron states (all
three orbitals overlayed)
5
Hybridized Bonds
sp1 hybridization
rare for elemental C

-
?
linear bonding
unchanged
one s one p orbitals ? 2 electron states
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Chemical Bonding

• Covalent between electronegative elements
• Metallic between electropositive elements
• Ionic between different elements with differing
  electronegativities
• Clear distinction between metallic non-metallic
• Ionic covalent somewhat qualitative boundary
• ionic chararacter 1 exp( -¼ (xA xB)2)
• xA, xB electronegativities

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Metallic Structures

• Goal Achieve as many bonds as possible
• Treat as the close-packing of hard spheres

1-D
2-D
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• Definitions
• Lattice point
• Unit cell
• Lattice parameters
• Atoms per unit cell
• Fractional coordinates
• Symmetry operations
• Coordination number

9
mirror
glide
a2
a1
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