LESSON-4-PROPERTIES-AND-TYPES-OF-SOLIDS-Copy.pdf

THE STRUCTURE OF CRYSTALLINE AND AMORPHOUS SOLIDS  A solid can be classified as crystalline or amorphous based on the arrangement of particles.  Classification of Solids Crystalline Amorphous Solids with highly Solids with regular...

THE STRUCTURE OF CRYSTALLINE AND AMORPHOUS SOLIDS  A solid can be classified as crystalline or amorphous based on the arrangement of particles.  Classification of Solids Crystalline Amorphous Solids with highly Solids with regular considerable arrangement of disorder in their components structure.  X-ray Diffraction is commonly used to determine the structure of a solid. X-ray Diffraction  Crystalline Solids A Lattice represents the regular positioning of the components of a crystal. A Lattice is the three dimensional system of points designating the positions of the components. The smallest repeating unit of the lattice is called the Unit Cell.  Crystalline are solids featuring highly ordered arrangements of their particles (atoms, ions, and molecules) in microscopic structures. These ordered microscopic structures make up a crystal lattice that accounts for the structure of the solid at any given point. Examples of crystalline solids include salt (sodium chloride), diamond, and sodium nitrate. Unit Cell-Simple Cubic, Body centered cubic & Face centered cubic.  Ionic Solids: metal and non metal Molecular solids: non metal and non metal Covalent Metallic solids Types of Crystalline Solid Ionic Solids: metal and non metal Ionic substances have ions at the point of the lattice that describe the structure of the compound. Examples: NaCl, FeSO4, Al2S3  Ionic solids, such as sodium chloride and nickel oxide, are composed of positive and negative ions that are held together by electrostatic attractions, which can be quite strong Figure 1.  have high melting points due to the very strong attractions between the ions they are hard,but also tend to be brittle, and shatter rather than bend. do not conduct electricity; however, they do conduct when molten or dissolved because their ions are free to move Metallic solids such as crystals of gold, copper, aluminum, and iron are formed by metal atoms Figure 2 Copper is a metallic solid.  atoms are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties All exhibit high thermal and electrical conductivity, metallic luster, and malleability.  Many are very hard and quite strong because of their malleability (the ability to deform under pressure or hammering), they do not shatter and, therefore, make useful construction materials.  The melting points of the metals vary widely. Mercury is a liquid at room temperature, and the alkali metals melt below 200 °C. post-transition metals also have low melting points, whereas the transition metals melt at temperatures above 1000 °C Covalent network solids include crystals of diamond, silicon, some other nonmetals, and some covalent compounds such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper).  minerals have networks of covalent bonds. The atoms in these solids are held together by a network of covalent bonds, as shown in Figure 3.  Covalent bonds are relatively strong, characterized by hardness, strength, and high melting points. For example, diamond is one of the hardest substances known and melts above 3500 °C.  Graphite is an exceptional example, composed of planar sheets of covalent crystals that are held together in layers by noncovalent forces. Unlike typical covalent solids, graphite is very soft and electrically conductive.  Molecular solid: non metal and non metal are composed of discrete molecules held together by intermolecular forces these interactions are relatively weak, tend to be soft and have low to moderate melting points. See ice →  Carbon dioxide (CO2) consists of small, nonpolar molecules and forms a molecular solid with a melting point of −78 °C. Iodine (I2) consists of larger, nonpolar molecules and forms a molecular solid that melts at 114 °C.  Small symmetrical molecules (nonpolar molecules), such as H2, N2, O2, and F2, have weak attractive forces and form molecular solids with very low melting points (below −200 °C). Substances consisting of larger, nonpolar molecules have larger attractive forces and melt at higher temperatures. Examples include ice (melting point, 0 °C) and table sugar (melting point, 185 °C).  Amorphous Solids the particles are not arranged in any specific order or the solids that lack the overall order of a crystal lattice. The term ‘amorphous’, when broken down into its Greek roots, can be roughly translated to “without form”. Many polymers are amorphous solids.  Plastics Glass Rubber Glass Polymers Gel Fused silica Pitch tar