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LECTURE 7.1

LECTURE 7.1. LECTURE OUTLINE. Weekly Deadlines Bonding and the Periodic Table. LESSON 07: BONDING AND THE PERIODIC TABLE. Ionic Bonding Covalent Bonding Metallic Bonding van der Waals Bonding Hydrogen Bonding. PRIMARY AND SECONDARY BONDS.

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LECTURE 7.1

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  1. LECTURE 7.1

  2. LECTURE OUTLINE • Weekly Deadlines • Bonding and the Periodic Table

  3. LESSON 07: BONDING AND THE PERIODIC TABLE Ionic Bonding Covalent Bonding Metallic Bonding van der Waals Bonding Hydrogen Bonding

  4. PRIMARY AND SECONDARY BONDS • Primary Bonds: Chemical (strong) bonding, involves the transfer or sharing of electrons: ionic, covalent, or metallic bonds. • Secondary Bonds: Physical (weak) bonding, does not involve the transfer or sharing of electrons: hydrogen and van der Waals bonds.

  5. DIRECTIONAL AND NON-DIRECTIONAL BONDS • Directional Bonds: Single or multiple bonds, which are localized and occur at fixed angles with respect to each other. • Non-Directional Bonds: Bonding is equally probable at all angles. The bond is not localized to a specific direction.

  6. THE THREE PRIMARY OR STRONG BONDS • Metal to Non-Metal: Ionic (Chapter 15) • Non-Metal to Non-Metal: Covalent (Chapter 16) • Metal to Metal: Metallic (Chapter 17)

  7. THE SECONDARY OR WEAK BONDS • van der Waals: Fluctuating dipoles (Chapter 18) • Hydrogen: Develops between “electropositive” and “electronegative” elements. Permanent dipoles (Chapter 19)

  8. THE IONIC BOND • The establishment of the “noble gas configuration” by electron transfer from metallic atoms to non-metallic atoms. The electrostatic bond is thus formed between positively charged metallic ions (cations) and negatively charged non-metallic ions (anions). • Ionic bonds are non-directional.

  9. THE IONIC BOND Ionic Bond: Arises from the electrostatic attraction between cations and anions. Because the cations are everywhere positive and the anions are everywhere negative, the bond is non-directional.

  10. THE IONIC BOND • Always produces compounds. Examples include NaCl (common salt), Na2O (natron), and MgO (magnesium oxide), where one species is metallic (the cation) and is from Groups I–III, or the transition metals, and the other species is non-metallic (the anion)* and is from Groups V–VII. Most importantly, ionically bonded solids are non-metallic and inorganic—they are ceramics. • * A Negative ION

  11. THE COVALENT BOND • The attainment of the "magical octet" of outer shell electrons by atoms sharing pairs of valence electrons. • Each shared electron pair constitutes a single bond. • Covalent bonds are directional. • Covalently bonded materials are non-metallic.

  12. THE COVALENT BOND Covalent Bond: Arises from the electrostatic attraction between cations/cation cores and shared electron pairs. The electrons are said to be localized, because they are confined, primarily between adjacent cations. Hence, the covalent bond is directional.

  13. THE COVALENT BOND • Occurs in non-metallic elements (Groups IV–VII) to form, for example, network solids (diamond carbon and silicon) and molecular gases (hydrogen, oxygen). • Covalent bonding also occurs in compounds, as in the network solids SiC (both Group IV elements), SiO2 (Groups IV and VI, respectively), and molecular gases (e.g., carbon dioxide).

  14. THE METALLIC BOND • The bonds formed between an array of positively charged metallic cations and a "sea" of negatively charged free electrons—the latter being "donated" from the outer shells of the constituent atoms. • Metallic bonds are non-directional. • Occurs for all metallic elements and their alloys (i.e., Group I, I and III metals, and for the transition metals) to form close-packed solids.

  15. THE METALLIC BOND Metallic Bond: Arises from the electrostatic attraction between cation cores and an electron cloud. The electrons are said to be delocalized, because they are not confined to any cation core, but are “free” to move between the cation cores. Hence, the metallic bond is non-directional.

  16. THE VAN DER WAALS BOND • Weak, secondary bond formed by the attraction of fluctuating dipoles between, for example, atoms of the noble gases and between molecules. Van der Waals bonds are non-directional.

  17. THE VAN DER WAALS BOND

  18. THE HYDROGEN BOND • Weak, secondary bond formed by the attraction of polar molecules. A polar molecule (or dipole) results from a permanent imbalance in the electron distribution in a molecule. This is between an electronegative atom (e.g., oxygen) and an electropositive atom (e.g., hydrogen). Hydrogen bonds are directional.

  19. THE COVALENT BOND AND WATER • The water molecule consists of one oxygen atom covalently bonded to two hydrogen atoms. • However, the oxygen atom attracts the shared electron pairs more strongly than do the hydrogen atoms, and the shared electrons “spend more time” with the oxygen atom. Hence, a permanent dipole develops with slightly positive charges on the hydrogen atoms and slightly negative charges on the oxygen atoms.

  20. THE HYDROGEN BOND AND THE CRYSTAL STRUCTURE OF ICE • The monomer of the ice structure consists of a central, covalently bonded molecule of water, which is hydrogen bonded to four other water molecules. • When the monomers are assembled to create the crystal structure of ice, a hexagonal material results.

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