atomic structures

• Materials


  Substances that make up the physical world, including metals, ceramics, polymers, and composites
• Stone Age


  • People used only natural materials, like stone, clay, skins, and wood
• Bronze Age


  • People found copper and how to make it harder by alloying, started around 3000 BC
• Iron Age


  • Use of iron and steel, a stronger material that gave advantage in wars, started at about 1200 BC
• Industrial Revolution


  • Discovery of a cheap process to make steel around 1850, enabled the railroads and the building of the modern infrastructure
• Materials Science


  Understanding of how materials behave and why they differ in properties, based on the atomistic understanding allowed by quantum mechanics
• Materials Engineering


  The development of materials science and the application of this knowledge to engineering applications
• Classification of materials


  • Crystalline materials (metals, ceramics)
  • Amorphous materials (glass, polymers)
  • Type of bonding
  • Molecular & crystal structure
  • Physical & mechanical properties
• Types of materials


  • Metals and alloys (iron, steel, copper, aluminum)
  • Polymers (plastics, rubber, nylon, polyethylene)
  • Ceramics & glasses (alumina, magnesia, silica, silicon carbide, silicon nitride)
  • Composites (wood, fiberglass)
• Metals


  Valence electrons are detached from atoms and spread in an 'electron sea' that "glues" the ions together. Metals are usually strong, conduct electricity and heat well, and are opaque to light (shiny if polished).
• Semiconductors


  The bonding is covalent (electrons are shared between atoms). Their electrical properties depend extremely strongly on minute proportions of contaminants. They are opaque to visible light but transparent to the infrared.
• Ceramics


  Atoms behave mostly like either positive or negative ions, and are bound by Coulomb forces between them. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides).
• Polymers


  Bound by covalent forces and also by weak van der Waals forces, usually based on H, C and other non-metallic elements. They decompose at moderate temperatures (100 – 400 C), and are lightweight.
• Composites


  Made of different materials in intimate contact to achieve specific properties.
• Biomaterials


  Any type of material that is biocompatible and used, for instance, to replace human body parts.
• Advanced materials


  Materials used in "High-Tec" applications, usually designed for maximum performance, and normally expensive.
• Examples of advanced materials

  • Titanium alloys for supersonic airplanes
  • Magnetic alloys for computer disks
  • Special ceramics for the heat shield of the space shuttle
• Structure


  Arrangement of atoms at the atomic level, and arrangement of small grains of material at the microscopic level
• Properties


  The way the material responds to the environment, including mechanical, electrical, magnetic, thermal, optical, and chemical properties
• Processing of materials


  Application of heat (heat treatment), mechanical forces, etc. to affect their microstructure and, therefore, their properties
• Modern material needs


  • High temperature structural materials for engine efficiency
  • Solutions for nuclear waste processing
  • Light, strong, and high temperature resistant materials for hypersonic flight
  • Optical fibers with negligible light absorption for optical communications
  • Unbreakable windows for civil construction
  • Strong and corrosion resistant materials for structures
• All engineering disciplines need to know about materials, even software and system engineering depend on the development of new materials
• Reasons to study materials

  • To be able to select a material for a given use based on considerations of cost and performance
  • To understand the limits of materials and the change of their properties with use
  • To be able to create a new material that will have some desirable properties
• Levels of material structure

  • Macro structure
  • Micro structure
  • Crystal structure
  • Atomic structure
• Atom


  Composed of electrons, protons, and neutrons. Electron and protons are negative and positive charges of the same magnitude.
• Atomic mass unit (amu)

  1/12 the mass of a carbon atom, equals 1.66 × 10-27 kg
• Mole


  The amount of matter that has a mass in grams equal to the atomic mass in amu of the atoms. The number of atoms in a mole is called the Avogadro number, Nav = 6.023 × 1023.
• Electrons in atoms


  Form a cloud around the nucleus, with only certain orbits allowed according to quantum mechanics. The structure is determined by the Pauli exclusion principle.

  
• Periodic table


  Elements are categorized by placing them in the periodic table. Elements in a column share similar properties.

  
• Categories of elements


  • Metals
  • Non-metals
  • Metalloids
• Metals


  • About 80% of the elements in the periodic table are metals because the outer most shells of these elements are not fully occupied and electrons move freely from one atom to another giving high electrical and thermal conductivity.
• Light metals


  • Soft and chemically reactive because they have only 1 or 2 electrons in the outer shell and give away these electrons very easily, resulting in low ionization energy.
• Noble gases


  • Have the last orbital fully filled and are chemically inert or inactive.
• 1. block elements


  • Have atoms in which the outermost d-orbital is filled.
• Categories of elements


  • Metals
  • Non-Metals
  • Metalloids
• Metalloids are elements that exhibit the properties of both metals and non-metals (B, Si, Ge, As, Sb, Te)
• Metals


  • About 80% of the metals in the periodic table are metals because the outer most shells of these elements are not fully occupied and electrons move freely from one atom to another giving high electrical and thermal conductivity
  • All the metals except mercury (Hg) are solid at room temperature
  • The light metals (s block elements — IA & IIA) are soft and chemically reactive because they have only 1 or 2 electrons in the outer shell and give away these electrons very easily. Hence, the ionization energy is very low
• Noble gases


  • The noble gases (group VIIIA - He, Ne, Ar, etc.,) have the last orbital fully filled and they are chemically inert or inactive
• 1. block elements


  • The d-block elements (groups IIIA - VIIA) have atoms in which the outermost d-orbital is filling. These elements need only a few electrons to complete their outer shell which they try to get from (or share with) the other atoms. Hence, the ionization energy of these elements is high and is mostly non-metallic
• Most non-metals are gaseous but bromine (Br) is a liquid