Dental Biomaterials I - Structure of Matter PDF

Course Title: Dental Biomaterials I Course Code:DBM011 Structure of Matter F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F A L L 2 0 2 3 Topics to be covered Atomic structure States of matter Types of bon...

Course Title: Dental Biomaterials I Course Code:DBM011 Structure of Matter F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F A L L 2 0 2 3 Topics to be covered Atomic structure States of matter Types of bonds A-Primary inter-atomic bonds B- Secondary bonds (van der Waals forces) Atomic solids and molecular solids Atomic arrangement of solids (Crystalline versus amorphous solids) Isomerism and Isomorphism Reconstructive versus displacive transformation Relationship between atomic bonding and the properties of solids Atom Nucleus Protons (+) Neutrons Responsible for atomic mass Electrons (-) Equal to number of protons Gives atomic number Valence electrons (outer shell) Determine type of bond, reactivity and properties v Valence Electrons: ü They are the outermost electrons. ü They determine the type of interatomic bonding. ü They determine chemical, mechanical, electrical and optical properties.  Atomic weight: It is the weight of protons + neutrons. Atomic Number: It is the number of proton = number of electrons States of matter Gas Liquid Solid Interatomic bond lowest Intermediate Highest Internal energy Highest Intermediate Lowest  Changes in states of matter Melting (solid to liquid) (Heat of fusion ) Solidification or freezing (liquid to solid) Latent heat of fusion Vaporization (liquid to gas) Condensation (gas to liquid Types of bonds Bonds Secondary Primary (Van der Waals forces) Ionic Permanent dipole Covalent Fluctuating dipole Metallic Primary Ionic bonds  Primary Ionic bonds (chemical bonds) Mechanism: Electrostatic attraction between positive and negative ions (metal and non-metal) Properties and characteristics Strong Water soluble (inorganic solvents) Insoluble in organic solvents Insulator for heat and electricity Its solution, conducts electricity Examples: Zinc oxide cements Primary covalent bonds  Primary covalent bonds Mechanism: Sharing of electrons (two non-metals) Properties and characteristics Very strong Highly directional Soluble in organic solvents Insoluble in water (inorganic solvent) Insulator for heat and electricity Examples: Polymers Primary Metallic bonds  Primary Metallic bonds Mechanism: Electron cloud (Two metals) Properties and characteristics Strong Ductile and malleable Good conductors for heat and electricity Shiny Opaque Examples: Cobalt chromium alloys, Gold alloys  Compare different types of primary bonds Ionic covalent Metallic Mechanisms Properties Examples Dental and general  Secondary bonds (physical weak attraction) Van der Waals forces Permanent dipole Fluctuating dipole Intermolecular bonds Intermolecular bond Asymmetric molecules Symmetric molecules Examples: Examples Hydrogen bonds in water molecules Inert gases Intermolecular bonds in hydrocarbons H2 or Cl2 Molecules Molecular solids versus atomic solids  Atomic arrangement (Crystalline vs amorphous solids)  Ingot, metal bar Crystal = grain= (space lattice) Unit cell Atomic arrangement (Crystalline vs amorphous solids) Crystalline Solids Amorphous solids Regular arrangement with repetition Atoms are random or have short range (long range arrangement) arrangement Low internal energy High internal energy Definite melting point Melting range [Starts softening at glass transition temperature (Tg) ] Examples: Examples Metals, Diamond, zirconia Wax, polymers, glasses Crystalline solids Cubic system types Axis A = B = C Angles all equal 90  TYPES OF SPACE LATTICE -There are about 14 types of space lattice -Unit cell: smallest repeating unit in the space lattice. - Classification of space lattice is according to: 1- length of axes of the unit cell (a,b,c) 2- Interfacial angles between the unit cell planes (α , β,δ) 1- Cubic system - The length of axes are equal (a=b=c ) - The interfacial angles equal 90o(α=β=δ = 90o) A-Simple cubic system: has one atom at each of 8 corners, each atom is sharing in 8 surrounding unit cells , therefore each atom has 1/8 of its volume in each unit cell Atomic packing =8x1/8=1 atom B-Body centered cubic (bcc): eg:Fe below 910 The unit cell has one atom at each of the 8 corners and an atom in the center Atomic packing =(8x1/8)+1=2 atoms C-Face centered cubic(fcc) e.g:Ag,Au,Cu,Pt,and Fe above 910 The unit cell has one atom at each of the 8 corners, and one in the center of each of the six faces Atomic packing=(8x1/8)+(6x1/2)=4 atoms 2- Tetragonal system -a =b # c - α=β=δ = 90o 3- Hexagonal system -a =b # c -Two of the interfacial angles are equal 90 and the third angle equals 120 (α=β = 90o ,δ=120o) In closed packed hexagonal (hcp) There are : -12 atoms at the corners, each atom has 1/6 of its volume in the unit cell -2 atoms :one at the bottom and one at the top of the unit cell -3 atoms in the center of the unit cell Atomic packing: (12x1/6)+(2x1/2)+3=2+1+3=6atoms e.g: Zn,Mg Atomic packing factor(APF)=Volume of atoms Volume of unit cell For bcc=0.68 For fcc=0.74 For hcp=0.74 As the atomic packing factor increases the density , strength and melting point of the metal increases. Crystalline solids Unit cell Atomic packing Atomic packing factor Crystalline solids Calculate Atomic packing for hexagonal close packed unit cell Isomerism (Allotropy & polymorphism) Allotropy Existence of the element in different crystalline arrangement Isomerism (Allotropy & polymorphism) Polymorphism Existence of compounds in different crystalline arrangement Reconstructive transformation Displacive transformation Involves bond breaking No bonds break Occurs slowly Occurs rapidly Accompanied by expansion Needs more energy Polymorphic forms have same chemical properties but different physical properties (densities , ,optical properties , coefficient of thermal expansion and contraction) Isomorphism: Is the opposite phenomenon of polymorphism Is the formation of identical crystal lattices by elements having different chemical composition Gold,copper,silver and (iron above 910OC) all exist as F.C.C. Correlation between structure and properties Density : increases with APF Thermal : Thermal conductivity ( metallic bond) Mechanical : Strength increases ( primary bonds) Electrical conductivity ( metallic bond) Optical ( opacity , lustrous -à metallic bonds)