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CHEMICAL BONDS

CHEMICAL BONDS. CHAP 9. Three Types of Chemical Bonds. Ionic bonds Electrons are transferred from one atom to another Occur between a metal atom and a nonmetal atom (2) Covalent bonds Electrons are shared between two atoms Occur between two nonmetal atoms Metallic bonds

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CHEMICAL BONDS

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  1. CHEMICAL BONDS CHAP 9

  2. Three Types of Chemical Bonds • Ionic bonds • Electrons are transferred from one atom to another • Occur between a metal atom and a nonmetal atom • (2) Covalent bonds • Electrons are shared between two atoms • Occur between two nonmetal atoms • Metallic bonds • Metal atoms share many electrons in a “sea” that is free to move throughout the metal

  3. 11 protons 11 electrons 11 protons 10 electrons Na+ Na 17 protons 18 electrons 17 protons 17 electrons Cl- Cl Formation of an ionic bond + e− Net reaction: Na + Cl → Na+Cl− + energy This energy is called the heat of formation

  4. Fig. 9.6 Model of the sodium chloride crystal No molecules in an ionic compound! NaCl is a “formula unit” + − Na+ ions Cl− ions

  5. Fig. 9.7 The cubic crystal structure of sodium chloride

  6. Ionic compounds consist of a combination of positive ions and negative ions • Ions are formed as metal atoms lose and nonmetal atoms gain electrons to achieve stable noble gas structure • The sum of the charges on the positive ions and negative ions in each formula unit must equal zero • How do we determine the formula for an ionic compound? • Key: All ionic formulas must be neutral!

  7. Electron dot notation for the representative elements Fig 8.18 Show only valence electrons!

  8. 2 x +3 = +6 1 x +2 = +2 3 x -2 = -6 2 x -1 = -2 Formula of Ionic Compounds Al2O3 Al and O Al3+ O2- Ca and Br CaBr2 Ca2+ Br-

  9. Why should two atoms share electrons? + 8e- 8e- 7e- 7e- F F F F F F F F lonepairs lonepairs single covalent bond single covalent bond lonepairs lonepairs Covalent bond - chemical bond in which two or more electrons are shared by two atoms. electronic structure of F2

  10. Fig. 9.8 Overlap of two atomic orbitals to form a molecular orbital

  11. single covalent bonds H H H H or H H O 2e- 2e- O 8e- O C O C O O double bonds 8e- 8e- 8e- double bonds O N N triple bond N N triple bond 8e- 8e- Electronic structure of water + + Double bond – two atoms share two pairs of electrons or Triple bond – two atoms share three pairs of electrons or

  12. How do we know if a bond between two atoms will be ionic or covalent? • In general: • metal and nonmetal → ionic bond • nonmetal and nonmetal → covalent bond • Specifically: • we use: Electronegativity- ability of an atom in a chemical bond to attract the electrons to itself

  13. Fig. 9.10 Electronegativities of the elements Very active nonmetals Very active metals

  14. Increasing difference in electronegativity Covalent Polar Covalent Ionic partial transfer of e- share e- transfer e- Classification of bonds by difference in electronegativity Table 9.5 Difference Bond Type Ionic ≥ 1.7 0.5 - 1.7 Polar Covalent 0.5 ≥ Covalent

  15. Fig. 9.11 Electron distribution and kinds of bonding

  16. F H Polar covalent bond or polar bond - a covalent bond with greater electron density around one of the two atoms electron rich region electron poor region

  17. Box Fig 9.1 How a microwave oven cooks food

  18. nucleus & inner shell e- mobile “sea” of e- Metallic Bonds • Held together by metallic bonds • Malleable and ductile • Good conductors of heat and electricity Cross Section of a Metallic Crystal

  19. Composition of Ionic Compounds Common names: “salt” → sodium chloride “lye” → sodium hydroxide “rust” → iron oxide “baking soda” → sodium bicarbonate “chalk” → calcium carbonate

  20. Fig. 9.12 Three substances containing sodium and some form of the carbonate ion

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