2-chemical structure of materials
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8/9/2019 2-Chemical Structure of Materials
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Chemical structure of
materials
1. Types of chemical bond2. Chemical structures of materials
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Types of chemical bond
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Atomic structure
ā¢ Bohr model
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Atomic structure
ā¢ Orbital
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Valence electrons
&
periodic table5
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Atomic bond
ā¢ Ftotal
ā Attractive force(FA)
ā Repulsive force(FR)
ā¢ Bond length
ā¢ Bond energy
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Primary bond
ā¢ Ionic bond
ā¢ Covalent bond
ā¢ Metallic bond
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Ionic bond
ā¢ Electronegativity(ģ źø°ģģ±ė) ģ°Øģ“ź° ķ° ģģź° ź²°ķ©
ā Alkali metal-halogen
ā¢ Electrostatic attraction, Coulombic force
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Ionic bond
ā¢ Potential energy versus internuclear distance
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Ionic bond
ā¢ Isotropic
ā¢ Ionic crystal
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Covalent bond
ā¢ Electronegativity(ģ źø°ģģ±ė) ģ°Øģ“ź° ģ ģ ė¹źøģ ģģź° ź²°ķ©
ā¢ Valence electrons ģė” ź³µģ
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Covalent bond
ā¢ ģģģ¤ģ¬ź³¼ ź³µģ ģ ģ ź°ģ ģ”“ģ¬ķź² ėė ķ
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Covalent bond
ā¢ Potential energy versus internuclear distance
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Covalent bond
ā¢ Three different ways to form an electron-pair bond
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Covalent bond
ā¢ Hybridization of s and p orbitals
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Covalent bond
ā¢ Hybridization of s and p orbitals
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Covalent bond
ā¢ Ļ bond, Ļ bond
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Covalent bond
ā¢ Ļ bond, Ļ bond
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Metallic bond
ā¢ źøģ ģģź° ź²°ķ©
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Metallic bond
ā¢ Electron-sea model
ā¢ Isotropic
ā¢ Ion coreģ ģ ģźµ¬ė¦ ź°ģ ģ ģ źø°ģ ģøė „
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Secondary bond
ā¢ ģ ģģ ģ“ėģ“ė ź³µģ ė„¼ ģė°ķģ§ ģė ė¶ģź° ģøė „
ā¢ Primary bondģ ė¹ķ“ ģ½ķ ź²°ķ©ė „
ā¢ ė¶ģģ ģź·¹ģ(dipole) : ģ¼ģģ , ģźµ¬ģ (ź·¹ģ±ė¶ģ)
ā¢ Van der Waals bond
ā¢ Hydrogen bond
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Secondary bond
ā¢ Hydrogen bond
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Bonding energy25
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Chemical structure of materials
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Solid materials
ā¢ Rigid structure
ā Component atoms, ions, or molecules are usually locked into place
ā¢ Extended three-dimensional patterns
ā¢ Allotrope
ā Diamond
ā Graphite ā C60
ā Carbon nanotubes
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Crystalline & amorphous
ā¢ Crystalline solid
ā Crystal lattice : regular repeating three-dimensional structure
ā¢ Amorphous solid : āshapelessā
ā No particular order
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Metallic structure
ā¢ Metallic bond
ā Free electron : high conductivity (electricity, heat)
ā Good mechanical properties
ā Crystal lattice : high ductility, tensile strength
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Unit cell
ā¢ Seven basic unit cells
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Defect
ā¢ Real crystals
ā Large numbers of defects (typically more than 104 per milligram)
ā¢ Point defect
ā¢ Line defect
ā¢ Plane defect
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Ceramic structures
ā¢ Two or more elements (compound) : ex) Al2O3
ā¢ Covalent and ionic bond, predominately ionic bonding ā Stronger than metallic bond
ā High hardness, high compressive strength, and chemical inertness
ā Low ductility and low tensile strength
ā¢ No free electron : low conductivity (electricity, heat)ā¢ Variable structures
ā¢ Charge balance
ā¢ Glassy or crystalline
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Ceramic structures
ā¢ Ceramic glass : ex) pure
SiO2 (tetrahedrons) ā Network of chain or ring
structures
ā Entirely glassy structure
ā No sharp melting or freezingpoint
ā High T : easily slide past eachother, viscous
ā Low T : rigid, hard and brittle
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Ceramic structures
ā¢ Ceramic crystalline or partially crystalline material
ā Most ceramicsā¢ Metallic and nonmetallic elements with ionic or covalent bonds
ā Silicate Ceramics (SiO2)
ā¢ Pyramid (tetrahedral or four-sided) units
ā Cement (19~25% SiO2, 5~9% Al
2O
3, 60~64% CaO, 2~4% FeO)
ā¢ One of the main ingredients of concrete
ā¢ Solution, recrystallization, and precipitation of a silicate structure
ā Nitride Ceramics
ā¢ High thermal and mechanical stability
ā¢
Cutting tools, wear-resistant partsā¢ TiN : cubic structure
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Defect
ā¢ Electroneutrality
ā Point defectsā¢ Frenkel defect
ā¢ Schottky defect
ā¢ Impurity ā both substitutional and interstitial
ā Linear Defects
ā¢ Dislocations
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Polymeric structure
ā¢ Monomer, repeating unit
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Polymeric structure
ā¢ Addition & condensation
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Polymeric structure
ā¢ Types by monomers
ā Homopolymer ā Copolymer
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Polymeric structure
ā¢ Types by structures
ā Linear polymer ā Branched polymer
ā Network(crosslinked) polymer
ā Dendrimer
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Chemical bonds ā Covalent + secondary bond
ā¢ Anisotropic
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Polymeric crystal
ā¢ Crystalline, semi-crystalline, amorphous
ā¢ Crystallinity
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Others
ā¢ Carbon materials
ā Crystalline :diamond, graphite, carbon nanotubes ā Glassy carbon
ā Pyrolytic carbon
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