1 / 34

Types of Solids

Types of Solids. Intermolecular Forces in Solids. The molecules in solids are held very tightly together, restricting their movement. This means that the intermolecular forces are significant. We can classify solids based on the type of intermolecular forces holding them together.

hilel-spencer
Download Presentation

Types of Solids

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Types of Solids

  2. Intermolecular Forces in Solids • The molecules in solids are held very tightly together, restricting their movement. • This means that the intermolecular forces are significant. • We can classify solids based on the type of intermolecular forces holding them together.

  3. Types of Solids • We will classify solids into four types: • Molecular Solids • Metallic Solids • Ionic Solids • Covalent network solids

  4. Molecular solids • A molecular solid is a solid that consists of atoms or molecules held together by intermolecular forces • Examples include: • Solid neon (melting point of -248oC) • Solid CO2 (dry ice) • Solid H2O (ice) • Iodine • Sugar

  5. Molecular solids • Consider the element Iodine, I2 • Iodine is a solid at room temperature and pressure • What intermolecular forces maintain this solid state? • Only London forces! • However, it has 53 electrons, giving it sufficient intermolecular force to be a solid at room temperature.

  6. Metallic solids • Metals usually have very high melting points, although this can be highly variable. • For example, mercury melts at -39oC while tungsten melts at 3410oC • Therefore, the intermolecular forces in metals must be rather strong. • These forces are not completely understood.

  7. Metallic solids • In metals, the valence electrons of neighbouring atoms form a sort of ‘sea of electrons’ • These electrons are called “delocalized electrons” • This ‘delocalized sea of electrons’ can be thought of as a ‘glue’ that holds the positive nuclei of the metal atoms together.

  8. Metal solids can be thought of as being like a rice krispy square The marshmallow is like the ‘delocalized sea’ that acts a glue that holds it together The rice krispies are like the positive nuclei of the metal atoms that compose the solid.

  9. Metallic solids • The positive nuclei of metals form lattice structures within the electron soup. • This means that metals are composed of crystals, but they are usually too small to see. • However, formation of metals through electroplating can make the crystalline nature more obvious.

  10. Gallium

  11. Ionic Solids • Consider sodium chloride (table salt) • An ionic solid is a solid that consists of cations and anions held together by the electrical attraction of opposite charges (ionic bonds) • This is technically considered an intramolecular force.

  12. Ionic Bonding • Ionic compounds have the following physical properties: • Very high melting points • Brittle • Non-conductive in a solid state • Conductive in a liquid state

  13. Ionic Bonding • The forces involved in ionic compounds are derived from the creation of a crystal lattice composed of alternating negative and positive ions. • Because of the full charge on ions, ionic bonds are stronger than dipole-dipole interactions

  14. Different Types of Crystal Lattices No, you don’t need to know these! They’re just neat lookin’

  15. Arrangement of Ions in a Sodium chloride cystal (cubic)

  16. Covalent Network Solid • Consider carbon dioxide (CO2) and silicon dioxide (SiO2). • What would you expect the physical properties of SiO2 to be? • CO2 b.p. = -78.5oC • If London forces are the only intermolecular force, then you might predict the b.p. of SiO2 to be slightly more than CO2.

  17. Covalent Network Solid • However SiO2 has a m.p. of 1650oC, and b.p. of 2230oC! • SiO2 is also known as quartz, or sand, is used in the production of glass. • Clearly, SiO2 is not a molecular solid like CO2 is. • SiO2 is a covalent network solid.

  18. Raw silica (SiO2)

  19. Silica glass (SiO2)

  20. Amethyst quartz (SiO2)

  21. Covalent Network Solid • A covalent network solid is a solid that consists of atoms held together in large networks or chains by covalent bonds. • Every atom is covalently bonded forming a 3-dimensional network • Examples include: diamond, graphite, silicon, asbestos

  22. Graphite • Graphite is an allotrope of carbon • It is a covalent network solid • It consists of ‘sheets’ of covalently bonded carbons • These sheets can slide over one another easily, making graphite useful for writing (i.e. it is the ‘lead’ in pencils!) • It also is also an electrical conductor.

  23. Diamond • Diamond is another allotrope of carbon. • Like graphite, it is a covalent network solid. • However, instead of sheets, it forms a 3-dimensional lattice of carbon atoms. • This is what gives diamond its characteristic hardness.

  24. Example Problem • Which of the four basic types of solids would you expect the following substances to be? • Silicon, Si • Cesium, Cs • Cesium iodide, CsI • Ammonia, NH3

  25. Answer • Silicon atoms might be expected to form covalent bonds with other silicon atoms. A covalent network solid would result. • Cesium is a metal; it is a metallic solid • Cesium iodide is an ionic substance; it exists as an ionic solid • Ammonia has a molecular structure, and is therefore a molecular solid

  26. Homework • Read section 4.6 page 268 • Page 273 • #1-7

More Related