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AP CHEMISTRY VIDEOS
Matter and Measurement
Atoms, Molecules and Ions
Stoichiometry- Calculations with Chemical Formulas and Equations
Aqueous Reactions and Solution Stoichiometry
Electronic Structure of Atoms
Periodic Properties of the Elements
Basic Concepts of Chemical Bonding
Molecular Geometry and Bonding
Intermolecular Forces, Liquids and Solids
Properties of Solutions
Additional Aspects of Equilibria
Bonding in Solids
=Bonding In Solids=
Molecular solids consist of atoms or molecules held together by weak intermolecular forces. The different forces consist of dipole-dipole forces, London dispersion forces, and hydrogen bonds. Due to the weakness of the forces the solids are considered weak. Most substances that are gases or liquids at room temperature form molecular solids at low temperatures. Some examples include sulphur, ice, sucrose, and solid carbon dioxide. Primarily all of the molecules are non-conductng when pure because they are unable to carry an electrical charge. These subsatnces are insoluble in water but are soluble in solvents that are non polar. But there are certain substances that are exceptions like ethanol that an dissolve in water.
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Covalent Network Solids
Covalent Network Solids consist of atoms held together in large networks by covalent bonds. Covalent bonds are much stronger than intermolecular bonds. Examples are diamonds, graphite, two allotropes of carbon, quartz, silicon, carbide and boron nitride. The carbon to carbon bonds keep diamonds unusual hardness. Also the melting point of a diamond is 3550 degrees Celcius. In graphite the electrons that move freely through the delocalized orbitals making graphite a great conductor. As you can see below, graphite has only 2-D hexagonal structure and therefore is not hard like diamond. The sheets of graphite are held together by only weak London forces!
Ionic solids consist of ions held together by ionic bonds. The strength of an ionic bond depends greatly on the charges of the ions. There are 4 different types of structures of simple ionic solids. The structure depends largely on the charges and the relative sizes of the ions.
Sodium ions have a coordination number of 6 because each sodium ion is surrounded by six nearest neighbor chloride ions.
Chlorine ions adopt a simple body-centered arrangement with each cesuim ion surrounded by eight chlorine ions.
Sulfur ions adopt a face-centered cubic arrangement, with the smaller zinc ions arranged so they are each surrounded tetrahedrally by four sulfur ions.
Calcium ions are shown in a face-centered cubic arrangement. There are twice as many fluorine ions as there are calcium ions.
Metallic solids consist entirely of metal atoms. They usually have hexagonal close-packed, cubic close-packed (face-centered cubic), or body-centered cubic structures. The bonding in metals is due to valence electrons that are delocalized throughout the entire solid. Metals vary greatly in the strength of their bonding. In general, however, the strength of the bonding increases as the number of electrons available for bonding increases. The mobility of the electrons explains why metals are good conductors of heat and electricity.
Chemistry, The Central Science
By Brown, LeMay, and Bursten
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