Structure of Matter and Atomic Structure - Sinai University

Sinai University Faculty of Oral and Dental Medicine Dental Biomaterial Department STRUCTURE OF MATTER AND ATOMIC STRUCTURE Outline And Objectives: A. By the end of this lecture, the student will be able to: 1. Identify the Structure of Matter. 2. Define Atomic Structure, Atomic Number And Know Pa...

Sinai University Faculty of Oral and Dental Medicine Dental Biomaterial Department STRUCTURE OF MATTER AND ATOMIC STRUCTURE Outline And Objectives: A. By the end of this lecture, the student will be able to: 1. Identify the Structure of Matter. 2. Define Atomic Structure, Atomic Number And Know Parts Of An Atom. 3. Recognize the Different Interatomic Bonds and Their Differences. 4. Differentiate Between Amorphous And Crystalline Structures. 5. Understand The Crystalline Lattice And Different Lattice Systems. STRUCTURE OF MATTER Structure Of Atoms The atom is the basic unit of internal structure for the material, The nucleus is composed of Protons: positively charged particles Neutrons: unchanged particles, The electrons are negatively charged particles revolving around the nucleus in a definite path ( state of energy ) which is the shells and subshells The atomic number of the element The number of protons and electrons should be equal in any atom The physical and chemical properties will depend on energetic interaction between the electrons lying furthermost from the nucleus (valence electron) The atomic weight It is nearly proportional to the weight of protons and neutrons in its nucleus It affects the density and specific heat, while it is very little effect on the mechanical properties. Interatomic attraction Interatomic attractions are associated with the electronic configuration of atoms. In any element, unlike the inert gases, the atom try to achieve the highly stable configuration of having eight electrons in the valance election shells. This configurations is obtained through one of the following. 1. Receiving extra electrons to complete the outer electron shell and becoming negatively charged ion 2. Releasing electrons so that the outer shell has eight electrons and becoming positively charged ion 3. Sharing electrons so that the outer shell of two or more atoms is complete Types of primary bonds primary bonds Covalent bond Ionic bond Metallic bond The electronic configuration which resulted from 1-Receiving extra electrons to complete the outer electron shell and the so becoming negatively charged ion 2- Releasing electrons so that the outer shell has eight electrons and becoming positively charged ion 3-Sharing electrons so that the outer shell of two or more atoms is complete give rise to strong atomic attraction or bonding called primary bonds within the molecule • the atoms are held together by strong intermolecular attractive force (Interatomic bonds ) Secondary bonds While the intermolecular bonds between molecules may be weak Covalent bonds Is the simplest and strongest bond And arises when atoms share their electrons, so that each electron shell achieves an inert gas structure The formations of bond for two hydrogen atoms H H H2 Ionic bonds It is the attraction of positive and negative ions e.g. Sodium Chloride (Na+ Cl- ) Na: atomic no.11 (2,8,1) ----Na+ (2,8) cation Cl: atomic no.17 (2,8,7)----Cl-(2,8,8) anion The sodium atom contain one valence electron in its outer shell and the chlorine atom has seven Electrons in its outer shell, Na - Cl Ionic bonds Na Cl + Na - Cl Fig( 2 )Formations of an ionic bond between sodium and chlorine Metallic bonds 1. It is the attractions between +cores and free electrons or electrons cloud . 2. It occurs in metals 3. The electrons more freely through the metal from atom to atom and from electron cloud . 4. There is attraction between free electrons and positive charged cores. Formation of a metallic bond , showing a cloud of electrons surrounding the nuclei. Fig (3) Secondary bonds ( VAN DER WAAL) forces These forces are physical, weak and arise from the polarization of molecules -ve pole+ ve pole formation of electrical dipoles ve pole- ve pole+ fig(4) Fluctuating dipole It is the attraction between +ve pole and -ve pole of two atoms in symmetric molecule such as inert gases Types of secondary bonds The electron field is constantly fluctuating ,the electrons of the atoms are distributed equally around the nucleus and produce an electrostatic field around the atom .However this field may fluctuate and as a result its charge becomes momentarily positive . (a fluctuating dipole( (A) fluctuating dipole Attraction between imbalance center ofve charge and the center of +ve charge in asymmetric molecules, where one atom can attract the electrons and become -ve and other atom becomes +ve in relation to it resulting in permanent dipole (B) PERMANENT DIPOLE Attraction between imbalance center of- ve charge and the center of +ve charge in asymmetric molecules, where one atom can attract the electrons and become -ve and other atom becomes +ve in relation to it resulting in permanent dipole e.g. H2o. when there is a covalent bond because oxygen and hydrogen atoms share electrons. ve oxygen pole+ve+ ve H H ve hydrogen pole+ Characteristics of Covalent bond 1. 2. 3. 4. Very strong and highly directional Resist inorganic solvents. Basic bond for polymers. Insulator Characteristics Ionic bonds 1- Heat resistant and insulators as solids. 2- Insoluble in organic solvents 3- Basic bond for glasses and ceramics. 4- In solutions they dissociate into their constituent ions and can easily dissolved in ionizing solvents such as water, acids, and alkalis. Characteristics of Metallic bond 1) High electrical and thermal conductivity 2) Opaque due to the free electron may absorb light 3) Reflective or lustrous due to the free electron reemit light. 4) It leads to crystalline arrangement in metals Types of solids a. Amorphous solids b. Crystalline solids A- Crystalline Solids Solid dental materials are termed crystalline when their atoms are regularly arranged in a space lattice. A space lattice Is the regular arrangement of atoms in the space so that every atom is situated similarly to every other atom. B) Amorphous solids Amorphous means without shape. Gases and liquids are amorphous substances. some solids like glass and some polymers are amorphous because of the random arrangement of their atoms. The solids are sometimes called “super cooled liquids”. Types of space lattices There are about 14 different types of space lattice but only few are of dental interest. The simplest way to study these types, is to consider a unit cell which is the smallest repeating unit in the space lattice. Classifications of unit cell Unit cells arc classified according to: A- The length of their axes (a, b, c). B- The interfacial angles (α, ß, ү).