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Chemical Bonding

Chemical Bonding. How compounds are held together. Review Questions. When representing a water molecule as H-O-H, what do the lines represent? Write e - configs for argon, chlorine, neon, and sodium Ar = 1s 2 2s 2 2p 6 3s 2 3p 6 Cl = 1s 2 2s 2 2p 6 3s 2 3p 5 Ne = 1s 2 2s 2 2p 6

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Chemical Bonding

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  1. Chemical Bonding • How compounds are held together

  2. Review Questions • When representing a water molecule as H-O-H, what do the lines represent? • Write e- configs for argon, chlorine, neon, and sodium • Ar = 1s2 2s2 2p6 3s2 3p6 • Cl = 1s2 2s2 2p6 3s2 3p5 • Ne = 1s2 2s2 2p6 • Na = 1s2 2s2 2p6 3s1 • Why is the phrase “sodium chloride molecule” incorrect?

  3. Objectives • Learn about ionic and covalent bonds and explain how they are formed • Learn about polar covalent bonds • Understand nature of bonds and their relationships to electronegativity • Understand bond polarity and how it is related to molecular polarity

  4. What is a BOND??? • Force holding two or more atoms together • Makes atoms function as a unit • Strength of the force = energy required to break bond = bond energy

  5. Types of bonding • Focus on two types of chemical bonds: • IONIC BONDING • COVALENT BONDING

  6. Ionic Bonding • Oppositely charged ions - strong bonding force • Electron is transferred to another atom • Metal + NonMetal • e- from Na transferred to Cl.  • Na atom stable (“looks” like Ne) • Cl is stable (“looks” like Ar)

  7. Covalent Bonds • Atoms share e- • 2 Cl atoms share e- • Both Cl stable (both “look” like Ar) • Occurs between non-metallic atoms

  8. Polar Covalent Bond • Sometimes, there is an unequal sharing of the electrons • Known as Polar Covalent bond. • Partial charge on atoms shown using lower case greek letter delta ∂

  9. Questions • What is meant by the term chemical bond? What subatomic particles are most important in bonds? • How are ionic bonds and covalent bonds different? • How is a polar covalent bond different from a covalent bond?

  10. Objectives • Learn about ionic and covalent bonds and explain how they are formed • Learn about polar covalent bonds • Understand nature of bonds and their relationships to electronegativity • Understand bond polarity and how it is related to molecular polarity

  11. Nature of bonds

  12. Electronegativity • Ability of atom in molecule to attract shared e- to itself • Increases going left to right across periodic table • Decreases going down a group

  13. Electronegativity • Range: Fluorine 4.0...Francium & Cesium 0.7 • Effect: Higher electronegativity of an atom, the closer shared e- will be to that atom when it forms a bond

  14. Electronegativity

  15. Bond Polarity • Bond Polarity depends on differencein electronegativity values of atoms forming bond • Atoms with very different electronegativities form very polar bonds • Ionic bonds areextreme case of bond polarity • Electronegativity difference greater than 2.0 considered ionic bond

  16. Bond Polarity Continuum

  17. Thinking question... • How do electronegativity trends compare to trends of atomic size?

  18. Problem • Arrange the following bonds in order of increasing polarity: H-H, O-H, Cl-H, S-H, F-H • H-H (2.1 - 2.1 = 0.0) • S-H (2.5 - 2.1 = 0.4) • Cl-H (3.0 - 2.1 = 0.9) • O-H (3.5 - 2.1 = 1.4) • F-H (4.0 - 2.1 = 1.9)

  19. Problems • For each of the following bond pairs, choose the one that is most polar • H-P & H-C • (2.1 - 2.1) < (2.5 - 2.1) • H-C • O-F & O-Cl • (4.0 - 3.5) = (3.5 - 3.0) • same • N-O & S-O • (3.5 - 3.0) < (3.5 - 2.5) • S-O • N-H & Si-H • (3.0 - 2.1) > (2.1 - 1.8) • N-H

  20. Match the compounds HF, NaCl, and O2 with the figures above • How do electronegativity values help in determining the polarity of a bond?

  21. Objectives • Learn about ionic and covalent bonds and explain how they are formed • Learn about polar covalent bonds • Understand nature of bonds and their relationships to electronegativity • Understand bond polarity and how it is related to molecular polarity

  22. Bond Polarity & Molecular Polarity • Molecule such as H-F that has a center of positive charge (∂+) and a center of negative charge (∂-) is said to have a dipole moment • Dipole moment represents molecular polarity • Any diatomic molecule with a polar bond has a dipole moment

  23. Some Polyatomic Molecules have dipole moments • Water is a polar molecule (it has a dipole moment) • Properties of H2O • surrounds and attracts both + and - ions • dissolves ionic substances • attract one another strongly (h-bonds) • high boiling temperature

  24. Questions • For each binary molecule given, indicate direction of its dipole moment. Some may have no dipole moment. • H-Cl • H-H • H-I • Br-Br • C-O

  25. Summary • Chemical bond = force holding 2 or more atoms together • Types of Bonds = Ionic and Covalent • Ionic = transfer of e- • Covalent = sharing of e- • Polar Covalent = unequal sharing of e- • Electronegativity = how much an atom “pulls” on e- • Polar bonds -> polar molecules

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