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Chapter 8

Chapter 8. Covalent Bonding. Let’s Review. What do we already know? What is a chemical bond? What is an ionic bond?. Section 1. The Covalent Bond. Stability. Lower energy is more stable Noble-Gas electron configuration Octet rule. Covalent Bond.

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Chapter 8

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  1. Chapter 8 Covalent Bonding

  2. Let’s Review • What do we already know? • What is a chemical bond? • What is an ionic bond?

  3. Section 1 The Covalent Bond

  4. Stability • Lower energy is more stable • Noble-Gas electron configuration • Octet rule

  5. Covalent Bond • Atoms in nonionic compounds share electrons • Covalent bond is the bond that results from sharing valence electrons • Molecule is formed when two or more atoms bond covalently

  6. H H Diatomic Molecules • Two atom molecules are more stable than one atom • H2, N2, O2, F2, Cl2, Br2, I2

  7. H H Hydrogen They Pair!!

  8. Hydrogen

  9. Oxygen

  10. Fluorine

  11. F F Fluorine

  12. Single Covalent Bonds • One pair of valence electrons is shared • Pair may be referred to as “bonding” pair • Also called sigma bonds • σ • Occurs when the shared pair is centered between the two atoms

  13. Bonding Orbital • Localized region where bonding electrons are most likely found

  14. Groups and Single Bonds • Group 17 • Group 16 • Group 15 • Group 14

  15. Homework (due Tuesday) • Draw the Lewis structures for the following molecules • PH3 • H2S • HCl • CCl4 • SiH4 • Challenge • Draw a generic Lewis Structure for a molecule formed between atoms of group 1 and group 16

  16. Homework continued • Draw LDS for • CH4 • Br2 • C6H14 also written as CH3(CH2)4CH3

  17. Multiple Covalent Bonds • Bond Order • Refers to the type of bond • Single Bond • Shares ONE pair of electrons • Double Bonds • Two pairs of electrons are shared • Triple Bonds • Three pairs of electrons are shared

  18. The Pi Bond • Multiple covalent bonds • Consist of at least one sigma and one pi bond

  19. Strength of Covalent Bonds • CB involve attractive and repulsive forces • Balance of the force is upset the bond can break • Several factors influence strength of cb

  20. Bond Length • Length depends on distance between bonded nuclei • Bond length is the distance two nuclei at the position of maximum attraction • Determined by: • Sizes of two bonding atoms • Number of electrons shared

  21. Bonds and Energy • Energy changes occur • When bonds are broken • Energy is released • Need energy put in to break it • Bond-dissociation energy • is the energy required to break a specific bond • Indicates strength of the bond • When bonds are formed

  22. Length and Energy • Shorter the length the greater the energy

  23. Energies of Chemical Reactions • Total energy is determined from energy of bonds broken and formed • Two types • Endothermic • Exothermic

  24. Energies of Chemical Reactions • Endothermic Reaction occurs when a greater amount of energy is required to break existing bonds in the reactants than is released when the new bonds formed. • Endothermic Reaction • More energy to break a bond than energy when bond is broken

  25. Energyin Energyout Energies of Chemical Reactions • Exothermic Bond

  26. Energies of Chemical Reactions • Exothermic reaction occurs when more energy is released during product bond formation than is required to break bonds in reactants. • Exothermic reaction • More energy is released than required to break the bonds

  27. Energyout Energyin Energies of Chemical Reactions • Endothermic Bond

  28. Section Two Naming Molecules

  29. Binary Molecular Compounds Example: N2O • First element in the formula is always named first, using the entire element name. • What is the first element? • Nitrogen

  30. Binary Molecular Compounds • The second element in the formula is named using its root and adding the suffix –ide. • What is the second element? • Oxygen • What will the name be? • Oxide

  31. Binary Molecular Compounds • Prefixes are used to indicate the number of atoms of each element are present in the compound. • How many nitrogens do we have? • Two • What will the prefix be? • Di- • What is the prefix plus the element? • Dinitrogen

  32. Binary Molecular Compounds • How many oxygens do we have? • One • What will the prefix be? • Mono • What is the prefix plus the element? • Monoxide

  33. Binary Molecular Compounds • What is the final answer? Dinitrogen monoxide

  34. How do we know what we are naming?

  35. HCl HClO3 H2S H2SO4 H2ClO2 Chlorous acid Sulfuric acid Hydrosulfuric acid Chloric acid Hydrochloric acid Pop Quiz Match the following correctly, also note if the acid is binary or an oxyacid: ··Hint·· ClO3 is chlorate

  36. Section Three Molecular Structure

  37. Molecular Formula • Shows the elements symbols and subscripts • PH3

  38. H P H H Lewis Structure

  39. Space-filling Molecular Model

  40. Ball-and-stick Molecular Model

  41. H P H H Structural Formula

  42. Molecular Formula • CH4

  43. H H C H H Lewis Structure

  44. Space-filling Molecular Model

  45. Ball-and-stick Molecular Model

  46. H H C H H Structural Formula

  47. Lewis Structures • BH3 • Nitrogen trifluoride • C2H4 • Carbon Disulfide • NH4+ • ClO4-

  48. Announcement • Print out chapter 8 review from teacher page. • Complete by Friday (will have time in class tomorrow to work on it) • Test Monday on sections 1,2,3

  49. Resonance Structures • Resonance • A condition that occurs when more than one valid Lewis structure can be written for a molecule or ion • Molecules and ions that undergo resonance behave as if there is only one structure

  50. Classwork • Page 260 • #53 • Page 274 • #84, 101, 102, 103, 104 • BONUS: 5 pts #137

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