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Covalent Bonding Chapter 8

Covalent Bonding Chapter 8. I. Molecular Compounds. In a covalent bond atoms are held together by sharing electrons. A molecule is a neutral group of atoms joined together by covalent bonds. A compound composed of molecules is called a molecular compound.

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Covalent Bonding Chapter 8

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  1. Covalent BondingChapter 8

  2. I. Molecular Compounds • In a covalent bond atoms are held together by sharing electrons. • A molecule is a neutral group of atoms joined together by covalent bonds. • A compound composed of molecules is called a molecular compound. • The molecules of a given compound are all the same.

  3. II. Molecular Formulas • A molecular formula shows how many atoms of each element a molecule contains. • The molecular formula does not tell you about a molecule’s structure.

  4. Ionic Compounds--Cation (Metal loses electron(s)--Anion (Non-metal gains electron(s)

  5. Examples: • Which of the following are covalent compounds? • NaBr • SiO2 • CO2 • AlCl3 • CH4

  6. III. Molecular Compound Properties • Molecular cpds tend to have relatively lower melting and boiling points than ionic cpds. • Many molecular cpds are gases or liquids at RT.

  7. Properties Table 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 Form electrolytes in solution odorous

  8. IV. Bond Polarity • Most bonds are a blend of ionic and covalent characteristics • Difference in electronegativity determines bond type

  9. IV. Bond Polarity • Electronegativity – Remember this? • Attraction an atom has for a shared pair of electrons • higher e-neg atom  - • lower e-neg atom +

  10. IV. Bond Polarity • Electronegativity Trend • Increases up and to the right.

  11. IV. Bond Polarity • Nonpolar Covalent Bond • e- are shared equally • usually identical atoms

  12. - + IV. Bond Polarity • Polar Covalent Bond • e- are shared unequally • results in partial charges

  13. IV. Bond Polarity • Nonpolar • Polar • Ionic View Bonding Animations.

  14. IV. Bond Polarity Examples: • Cl2 • HCl • NaCl 3.16-3.16=0.0 Nonpolar 3.16-2.20=0.96 Polar 3.16-0.93=2.23 Ionic

  15. V. Octet Rule in Covalent bonding • In covalent bonds, electron sharing usually occurs so that atoms attain the electron configuration of noble gases. • Combinations of atoms of the nonmetals and metalloids in groups 14-17 of the periodic table are likely to form covalent bonds.

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

  17. VI. Single Covalent Bonds • An electron dot structure 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

  18. IV. 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 of a nonbonding pair. Lone pair

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

  20. VII. Double and Triple Covalent Bonds

  21. Lewis Structures • Predict the location of certain atoms • Determine the number of electrons available for bonding • Place bonds to form the skeletal structure • Determine the number of valence electrons remaining • Determine whether the central atom satisfies the octet rule

  22. Lewis Structures • The chemical symbol for the element is surrounded by a number of dots corresponding to number of valence electrons

  23. X. Lewis Structures for Covalent Compounds • In a covalent compound, electrons are shared between atoms to form a covalent bond in order that each atom in the compound has a share in the number of electrons required to provide a stable, Noble Gas, electronic configuration. • Electrons in the Lewis Structure (electron dot diagram) are paired to show the bonding pair of electrons. Katie loves mrschilton!

  24. X. Lewis Structures for Molecular Compounds • Carbon fluoride • CF4 + 4 =

  25. Lewis Structures for Ionic Compounds • The overall charge on the compound must equal zero, that is, the number of electrons lost by one atom must equal the number of electrons gained by the other atom. • The Lewis Structure (electron dot diagram) of each ion is used to construct the Lewis Structure (electron dot diagram) for the ionic compound.

  26. X. Lewis Structures for Ionic Compounds

  27. Practice! • Sulfur trioixide • Boron trifluoride • Carbonate

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

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