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I. Introduction to Bonding

Chemical Bonding. I. Introduction to Bonding. OBJECTIVES. 2.4.1 Define chemical bond 2.4.2 Explain why most atoms form chemical bonds. 2.4.3 Describe ionic and covalent bonding. 2.4.4 Classify bonding type according to electronegativity differences

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I. Introduction to Bonding

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  1. Chemical Bonding I. Introduction toBonding

  2. OBJECTIVES 2.4.1 Define chemical bond 2.4.2 Explain why most atoms form chemical bonds. 2.4.3 Describe ionic and covalent bonding. 2.4.4 Classify bonding type according to electronegativity differences 2.4.5 Define molecule and molecular formula.

  3. Review • We can also predict what ions an element will form. +1 +/-4 0 +2 -3 -2 -1 +3 multiple cations

  4. Vocabulary • Chemical Bond • electrical attraction between nuclei and valence e- of neighboring atoms that binds the atoms together • bonds form in order to… • increase stability

  5. Vocabulary Octet Rule: Atoms will transfer or share electrons in order to have 8 electrons in their highest energy level. • This makes it like a noble gas

  6. Vocabulary CHEMICAL FORMULA IONIC COVALENT Formula Unit Molecular Formula NaCl CO2

  7. Vocabulary COMPOUND more than 2 elements 2 elements Binary Compound Ternary Compound NaCl NaNO3

  8. Vocabulary ION 2 or more atoms 1 atom Monatomic Ion Polyatomic Ion Na+ NO3-

  9. Types of Bonds COVALENT IONIC e- are transferred from metal to nonmetal e- are shared between two nonmetals Bond Formation Type of Structure true molecules crystal lattice Physical State liquid or gas solid Melting Point low high Solubility in Water yes usually not yes (solution or liquid) Electrical Conductivity no Other Properties

  10. Types of Bonds METALLIC e- are delocalized among metal atoms Bond Formation Type of Structure “electron sea” Physical State solid Melting Point very high Solubility in Water no yes (any form) Electrical Conductivity malleable, ductile, lustrous Other Properties

  11. Quick Hint • All covalent bonds are between two non-metals • All ionic bonds are between a metal (cation) and a nonmetal (anion). • All metallic bonds are between two metals

  12. Lewis Structure • Covalent – show sharing of electrons • Ionic – show transfer of electrons

  13. Lewis Structures • Covalent – show sharing of electrons • Ionic – show transfer of electrons

  14. Ionic Nomenclature – Ionic Formulas • Write each ion, cation first. Don’t show charges in the final formula. • Overall charge must equal zero. • If charges cancel, just write symbols. • If not, use subscripts to balance charges. • Use parentheses to show more than one polyatomic ion. • Stock System – Roman numerals indicate the ion’s charge

  15. Ionic Nomenclature – Ionic Names • Write the names of both ions, cation first. • Change ending of monatomic ions to –ide. • Polyatomic ions have special names. • Stock System – Use Roman numerals to show the ion’s charge if more than one is possible. Overall charge must equal zero.

  16. Ionic Nomenclature • Consider the following: • Does it contain a polyatomic ion? • -ide, 2 elements  no • -ate or –ite, 3+ elements  yes • Does it contain a Roman numeral? • Check the table for metals not in Groups 1 or 2. • No prefixes.

  17. Ionic Nomenclature • Potassium chloride • K+ Cl- KCl • Magnesium nitrate • Mg2+ NO- Mg(NO3)2 • Copper (ii) chloride • Cu2+ Cl- CuCl2

  18. Ionic Nomenclature • NaBr • Sodium bromide • Na2CO3 • Sodium carbonate • FeCl3 • Iron (III) chloride

  19. Covalent Bonding • Covalent bonds can have multiple bonds. • Single Covalent Bond • Chemical bond resulting from sharing of an electron pair between two atoms

  20. Double Covalent Bond • Chemical bond resulting from sharing of two electron pairs between two atoms

  21. Triple Covalent Bonds • Chemical bond resulting from sharing of three electron pairs between two atoms

  22. Molecular Nomenclature • Prefix System (Binary system) • Less electronegative atom comes first. • Add prefixes to indicate number of atoms. Omit mono- prefix on first element. • Change the ending of the second element to –ide.

  23. Molecular Nomenclature Prefixes • Mono- 1 • Di- 2 • Tri- 3 • Tetra- 4 • Penta- 5 • Hexa- 6 • Hepta- 7 • Octa- 8 • Nona- 9 • Deca- 10

  24. Molecular Nomenclature • CCl4 • Carbon tetrachloride • N2O • Dinitrogen monoxide • SF6 • Sulfur hexaflouride

  25. Molecular Nomenclature • Arsenic trichloride • AsCl3 • Dinitrogen monoxide • N2O5 • Tetraphosphorus decoxide • P4O10

  26. Bond Polarity • Most bonds are a blend of ionic and covalent characteristics. • Differences in electronegativity determines bond type.

  27. Bond Polarity • Electronegativity • Attraction an atom has for a shared pair of electrons. • higher e-neg atom  - • lower e-neg atom +

  28. Dipole Movement • Dipole Moment - a measure of the polarity of a bond. • Is often represented by a special arrow. • Arrow points to more EN atom.

  29. Bond Polarity • Electronegativity Trend (p. 151) • Increases up and to the right.

  30. Bond Polarity • Nonpolar Covalent Bond • e- are shared equally • symmetrical e- density • usually identical atoms

  31. - + Bond Polarity • Polar Covalent Bond • e- are shared unequally • asymmetrical e- density • results in partial charges (dipole)

  32. Bond Polarity • Ionic Bond • e- are not shared • results in charged particles • opposite charges attract

  33. Determining Type, DEN 0.3 1.7 5% 50%

  34. Determining Type, DEN • Ionic, Polar or Nonpolar Covalent Compounds:The difference in electronegativity between bonding atoms leads to the type of compound. Example: • O2 , O=O ENO = 3.5 D EN = 0g • NO, N=O ENN = 3.0, ENO = 3.5 D EN = .5g • CO, C= O ENC = 2.5, ENO = 3.5 D EN = 1.0g • NaCl, Na+Cl- ENNa = 0.9, ENCl = 3.0 D EN = 2.1g Nonpolar Covalent Polar Covalent Polar Covalent Ionic

  35. Sample Problem • Use electronegativity differences to classify bonding between sulfur, S, and the following elements: hydrogen, H; cesium, Cs; and chlorine, Cl. In each pair, which atom will be more negative? Bonding between sulfur and Electronegativity difference More-negative atom Bond type hydrogen 2.5 – 2.1 = 0.4 Polar-covalent sulfur cesium 2.5 – 0.7 = 1.8 Ionic sulfur chlorine 3.0 – 2.5 = 0.5 Polar-covalent chlorine

  36. Additional Sample Problems • Complete the following chart: Elements bonded Electronegativity difference More-negative atom Bond type a. C and H 2.5 – 2.1 = 0.4 Polar-covalent carbon b. C and S 2.5 – 2.5 = 0 Nonpolar covalent Same electronegativity c. O and H 3.5 – 2.1 = 1.4 Polar-covalent oxygen d. Na and Cl 3.0 – 0.9 = 2.1 Ionic chlorine e. Cs and S 2.5 – 0.7 = 1.8 Ionic sulfur

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