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The Octet Rule in Covalent Bonding

The Octet Rule in Covalent Bonding

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The Octet Rule in Covalent Bonding

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  1. 8.2 The Octet Rule in Covalent Bonding • The Octet Rule in Covalent Bonding • What is the result of electron sharing in covalent bonds?

  2. 8.2 The Octet Rule in Covalent Bonding • In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.

  3. 8.2 Single Covalent Bonds • Two atoms held together by sharing a pair of electrons are joined by a single covalent bond.

  4. 8.2 Single Covalent Bonds • An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots. • A structural formula represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms.

  5. 8.2 Single Covalent Bonds • The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.

  6. 8.2 Single Covalent Bonds • A pair of valence electrons that is not shared between atoms is called an unshared pair, also known as a lone pair or a nonbonding pair.

  7. 8.2 Single Covalent Bonds • The hydrogen and oxygen atoms attain noble-gas configurations by sharing electrons.

  8. 8.2 Single Covalent Bonds • The ammonia molecule has one unshared pair of electrons.

  9. 8.2 Single Covalent Bonds • Methane has no unshared pairs of electrons.

  10. 8.1 Section Assessment

  11. Section Assessment

  12. 8.1 Section Assessment

  13. for Conceptual Problem 8.1 Section Assessment Problem Solving 8.8 Solve Problem 8 with the help of an interactive guided tutorial.

  14. 8.2 Double and Triple Covalent Bonds • Double and Triple Covalent Bonds • How do atoms form double or triple covalent bonds?

  15. 8.2 Double and Triple Covalent Bonds • Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.

  16. 8.2 Double and Triple Covalent Bonds • A bond that involves two shared pairs of electrons is a double covalent bond. (ex: O2 has a double covalent bond between the two oxygen atoms) • A bond formed by sharing three pairs of electrons is a triple covalent bond. (ex. N2 has a triple covalent bond between the two nitrogen atoms)

  17. 8.2 Double and Triple Covalent Bonds • O2 molecule: Each oxygen atom has two unshared pair of electrons. N2 molecule: Each nitrogen has one pair of unshared electrons • Lewis dot structure of O2 and N2

  18. 8.2 Double and Triple Covalent Bonds • Carbon dioxide gas is soluble in water and is used to carbonate many beverages. A carbon dioxide molecule has two carbon-oxygen double bonds.

  19. 8.2 Double and Triple Covalent Bonds • Carbon dioxide is an example of a triatomic molecule.

  20. 8.2 Coordinate Covalent Bonds • Coordinate Covalent Bonds • How are coordinate covalent bonds different from other covalent bonds?

  21. 8.2 Coordinate Covalent Bonds • In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.

  22. 8.2 Coordinate Covalent Bonds • A coordinate covalent bond is a covalent bond in which one atom contributes both bonding electrons. • In a structural formula, you can show coordinate covalent bonds as arrows that point from the atom donating the pair of electrons to the atom receiving them.

  23. 8.2 Section Assessment

  24. 8.2 Section Assessment

  25. 8.2 Section Assessment

  26. 8.2 Coordinate Covalent Bonds • A polyatomic ion, such as NH4+, is a tightly bound group of atoms that has a positive or negative charge and behaves as a unit. One of its bonds is a coordinate covalent bond. • Most plants need nitrogen that is already combined in a compound to grow.

  27. Bonding in: NaCl ? HCl ? H2O ? Bonding in ionic compounds containing polyatomic ions: Na2CO3 ? BaSO4 ? NH4Cl ?

  28. 8.2 Bond Dissociation Energies • Bond Dissociation Energies • How is the strength of a covalent bond related to its bond dissociation energy?

  29. 8.2 Bond Dissociation Energies • The energy required to break the bond between two covalently bonded atoms is known as the bond dissociation energy. • A large bond dissociation energy corresponds to a strong covalent bond.

  30. Other Theories of Bonding? • The octet rule does not allow us to understand bonding in ALL molecules. • Resonanceis a concept used to explain some of the compounds that do not conform to the octet rule (Ex. Ozone O3) • Other theories? Molecular Orbital Theory

  31. 8.2 Resonance • Ozone in the upper atmosphere blocks harmful ultraviolet radiation from the sun. At lower elevations, it contributes to smog.

  32. 8.2 Resonance • The actual bonding of oxygen atoms in ozone is a hybrid, or mixture, of the extremes represented by the resonance forms.

  33. 8.2 Resonance • A resonance structure is a structure that occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion.

  34. 8.2 Exceptions to the Octet Rule • Exceptions to the Octet Rule • What are some exceptions to the rule? • The octet rule cannot be satisfied in molecules whose total number of valence electrons is an odd number (ex. NO2) There are also molecules in which an atom has fewer (ex, BF3), or more (ex. SF6; PCl5), than a complete octet of valence electrons.

  35. 8.2 Section Quiz. • 8.2.

  36. 8.2 Section Quiz. • 1. In covalent bonding, atoms attain the configuration of noble gases by • losing electrons. • gaining electrons. • transferring electrons. • sharing electrons.

  37. 8.2 Section Quiz • 2. Electron dot diagrams are superior to molecular formulas in that they • show which electrons are shared. • indicate the number of each kind of atom in the molecule. • show the arrangement of atoms in the molecule. • are easier to write or draw.

  38. 8.2 Section Quiz • 3. Which of the following molecules would contain a bond formed when atoms share three pairs of electrons? • Se2 • As2 • Br2 • Te2

  39. 8.3 VSEPR Theory • VSEPR Theory • How does VSEPR theory help predict the shapes of molecules?

  40. 8.3 VSEPR Theory • The hydrogens in a methane molecule are at the four corners of a geometric solid. All of the H—C—H angles are 109.5°, the tetrahedral angle. (See Models)

  41. 8.3 VSEPR Theory • The valence-shell electron-pair repulsion theory, or VSEPR theory, explains the three-dimensional shape of methane.

  42. 8.3 VSEPR Theory • According to VSEPR theory, the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible. • HCl, Cl2 are linear diatomic molecules • CO2 is linear triatomic • H2O has a bent shape, NH3 has a pyramidal shape and CH4 has a tetrahedral shape. • Activity: Molecular Models Lab

  43. 8.3 VSEPR Theory • NH3 has a pyramidal shape and the measured H—N—H bond angle is about 107. • (See Models)

  44. 8.3 VSEPR Theory • H2O has a bent shape and the measured bond angle in water is about 105°. (See Models)