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Lecture 19

Solids. Solutions. Crystals van der Waals forces Solvents and Solubles. Lecture 19. Solids. Solids consist of atoms, ions, or molecules packed closely together and held by electric forces. Most solids have crystalline structure. The crystals of a given kind has the same geometric form. .

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Lecture 19

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  1. Solids. Solutions. Crystals van der Waals forces Solvents and Solubles Lecture 19

  2. Solids Solids consist of atoms, ions, or molecules packed closely together and held by electric forces. Most solids have crystalline structure. The crystals of a given kind has the same geometric form. Irregularly arranged solids are called amorphous. Crystalline solids melt at a specific temperature. Amorphous solids soften gradually when heated.

  3. Types of Crystals Crystalline solids are classified by the type of bonding: ionic, covalent, metallic, and molecular. Ionic bonds occur between metals and nonmetals. Crystals can be face-centered or body-centered. In covalent crystals, electrons are equally shared by the involved atoms.

  4. The Metallic Bond Metals have one or few electrons loosely attached to the nucleus. In a metallic solid atoms share their electrons  the electrons form a common “gas” The electron gas moves freely through metal ions.

  5. In general molecules are stable and do not tend to transfer or share electrons. Molecular Crystals Molecules form liquids and solids due to van den Waals forces. Van der Waals forces account for small departures of the behavior of real gases from the ideal gas law.

  6. Nature of the van der Waals forces Molecules can be connected by polar covalent bonds. Three types of interactions between molecules Polar  polar molecules (H2O) Polar nonpolar Nonpolar  nonpolar Since van der Waals bonds are much weaker than ionic, covalent, or metallic bonds, molecular crystals have: low melting and boiling points and little mechanic strength.

  7. Solutions In a solution of 2 substances: Solvent is the one present in larger amount (water) Solute is the other Concentration is the amount of solute in a given amount of solvent. Difference between compounds and solutions: Compounds have fixed compositions, solutions do not. Solubility of a substance is the maximum amount that can be dissolved in a given quantity of a particular solvent at a given temperature and pressure.

  8. Saturated Solutions A solution that contains the maximum amount of solute possible is called saturated. Solubility of gases in liquids decreases with increasing temperature. Example: bubbles escaping from boiling water

  9. Types of Liquids Liquids can be polar (water) and nonpolar (gasoline). The molecules of polar liquids can join together and with those of other substances. The structure allows substances to dissolve in polar liquids. Molecules of fats and oils are nonpolar  they do not interact with water molecules  layer formation on the surface of water Soap molecules are negatively charged at one end and nonpolar at the other  in water they form clusters with the nonpolar ends inside  nonpolar particles are absorbed inside clusters

  10. Summary Solids can be crystalline and amorphous with 4 types of bonds (ionic, covalent, metallic, and molecular) van der Waals forces help to form molecular crystals Solutions have no fixed compositions and may unsaturated, saturated, and supersaturated

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