Structure of Matter PDF

 Structure of matter Dr/Diaa Elmwafy The atom is composed of:- A-The nucleus: protons (+ve) neutrons(uncharged) B-Electrons (-ve)  The atom is the basic unit of internal structures  The physical & chemical properties depends on interaction between electrons lying fur...

 Structure of matter Dr/Diaa Elmwafy The atom is composed of:- A-The nucleus: protons (+ve) neutrons(uncharged) B-Electrons (-ve)  The atom is the basic unit of internal structures  The physical & chemical properties depends on interaction between electrons lying furthermost from the nucleus termed (Valence electrons).  Any element except inert gases try to achieve the highly stable configuration to having 8 electrons in the outer or valance electron shell stable through receiving (- ve charged) , or giving (+ve charged), or share electrons so the outer shell of 2 or more atoms become complete.  Inter Atomic bonding is 1ry bond Strong intramolecular Types: Covalent, ionic, metallic  Intermollecular is 2ry bond: weak Types: Vander waals forces A)Covalent bond: Sharing electrons H2 gas molecule Very strong, Insulator Basic bond for polymers B) Ionic bond: Electrostatic attraction ( ) unlike charge NaCl molecule → Na+ cation, CL- anion Insulator & heat resistant Basic bond for ceramics & glasses C) Metallic bond: Metal atoms give up electrons (loosely held and are free to move about all atoms in their valence shells. Metalllic bond consists of +ve ion cores held together by electron clouds which diffuse freely around the +ve cores→ easy defomability of metals and other properties.  High thermal and electric conductivity  Opaque bec. free electrons may absorb light.  Reflective or lustrous bec. electrons reemit light  Van der Waals forces: E.g H2O molecule  Combination of ionic & covalent: Caso4  Combination of metallic & ionic : Dental Amalgam  High conductive properties, hard & brittle  Interatomic distance: Caused by interatomic repulsive & attractive forces Factors affecting IAD: Temp: ↑ → ↑ energy → ↑ IAD No. of adjacent atoms: ↑ → ↓ IAD covalent bonding: ↑ (shared e’ no.)→ ↓ IAD State of matter Free movement of electrons → ↑ energy →↑ IAD Gas > Liquid > Metal Structure of solids  Solid substances are classified according to the internal atomic structure, depending on the regularity of the atoms or molecules in the three spatial directions, into:- 1-Crystalline 2-Amorphous (non crystalline) 3-Semi Crystalline (Mesomorphous)  1-Crystalline The atoms are arranged regularly & repetitively in the 3-dimensions. Space lattice: The arrangement of atoms in 3D → each atom has a position similar to every other atom. Atomic arrangement may take one of seven main crystal patterns (Cubic, tetragonal, orthorhombic, Monoclinic, Triclinic, Hexagonal, Rhombohedral). Unit cell is the smallest repeated unit in a crystal lattice. The type of space lattice is defined by the length of 3 axes of unit cell and the angles ( ) them 1-Simple cubic: (SC) Each atom in each corner of the 8 corners is associated with 8 surrounding unit cells→ Each atom participating in 8 unit cells → each atom has 1/8 of its volume in each of theses 8 cells → SC contains one metal atom per unit cell 8 atoms * 1/8 at each corner= 1 atom 2-Body centered cubic: (BCC) The unit cell has an atom at each corner of the 8 corners of the cube and another atom at the center of the unit cell→ There are 2 atoms per unit cell in BCC. 8 atoms * 1/8 at each corner + 1 atom in the center = 2 atoms Number of atoms in a space lattice (Body centered cubic space lattice) BCC has 2 atoms per unit cell [ (8x1/8) + 1] , e.g. iron, chromium. 3-Face centered cubic: (FCC) The unit cell has an atom at each corner of the 8 corners of the cube and another atom at the center of each face of the unit cell. At the center of each face the atom share 2 unit cells & thus its value may be as a ½ atom→ There are 4 atoms per unit cell in FCC. 8 atoms * 1/8 at each corner + 6 atom * ½ in the center = 4 atoms  Number of atoms in a space lattice (Face centered cubic space lattice) FCC has four atoms per unit cell [(8x1/8) + (6x1/2], e.g. copper, gold, platinum, and silver.. The atoms or molecules are positioned randomly in space without regularity or repetetion , such as in gases and liquids. 1- Higher internal energy: 2- No definite melting temperature: but they gradually soften as temperature is raised and gradually harden as cool. They have glass transition temperature (Temperature above which a sharp increase in the coefficient of thermal expansion occurs indicating increased molecular mobility) The atoms or molecules are arranged with a definite regularity in one or more directions, but not in all of the three directions. e.g. Pyrolytic carbon  Polymorphism Many materials have the same chemical composition, these different polymorphic forms may be called allotropic forms E.g. of allotrophy in dentistry is silica. Quratz (hexagonal) at 870 c→ Tridymite (rhombohedral) at 1470 c→ cristobalite (cubic) at 1713 c→ fused quartz (amorphus).  Imperfections in crystalline solids 1-Point defect: a-Vaccancy: In which an atom is missing within a crystal ( due to imperfect packing during the original crystallization or may arise from thermal vibrations of the atoms at elevated temp., bec. as thermal energy ↑→↑ probability that individual atoms will jump out of their positions of lowest energy) b-Intersitial impurities: in which an extra atom may be lodged within a crystal structure A and B → atomic distortion within the crystal lattice 2-line defect: As dislocation It is the displacement of a raw of atoms from their normal positions in the lattice. N.B. Plastic deformation in metals occurs by motion of dislocation. 3-Plane defects: Such as grain boundaries in metals Thank you