Attractions Between Particles


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Attractions Between Particles

  1. 1. Attractions between Particles Chapter 6, Holt Modern Chemistry Lisa Allen
  2. 2. Chemical bond types <ul><li>Covalent bonds: Shared valence electrons </li></ul><ul><li>Ionic bonds: Attractions between oppositely charged particles </li></ul><ul><li>Metallic bonds: Bonds formed when atoms are held together by a shared “sea of electrons” </li></ul>
  3. 3. Useful sites <ul><li> </li></ul><ul><li> </li></ul>
  4. 4. Covalent bonds <ul><li>Occurs between atoms of similar electronegativity (  <0.3) </li></ul><ul><li>Molecules are formed by covalent bonds </li></ul><ul><li>Equal sharing of electrons makes for strong bonds. </li></ul><ul><li>Strong bonds are short bonds. Bond length and bond energy are inversely related </li></ul>
  5. 5. Covalent molecules
  6. 6. Covalent crystals? <ul><li>Diamonds are strong because they are covalently bonded, but they form a crystal. </li></ul><ul><li>The carbon atoms in a diamond are bonded to 4 other carbon atoms in a “covalent network crystal” </li></ul><ul><li>See page 340 for more explanation of this. </li></ul><ul><li>Don’t let this confuse you! Most covalent bonds form simple molecules, like sugar; not covalent network crystals like diamonds! </li></ul>
  7. 7. Ionic bonds <ul><li>Occurs between atoms of very different electronegativity (  >1.7) </li></ul><ul><li>Ionic compounds are formed from these bonds. There are MANY atoms in the compound. </li></ul><ul><li>Unequal sharing of electrons makes for less strong bonds. </li></ul>
  8. 8. Ionic humor?
  9. 9. Vocabulary associated with ionic bonds <ul><li>Crystal lattice: </li></ul><ul><li>Formula unit: </li></ul><ul><li>Lattice energy: </li></ul><ul><li>Dissociate: </li></ul><ul><li>Conductivity: </li></ul>
  10. 10. Vocabulary associated with ionic bonds <ul><li>Crystal lattice: Structure of ionic compounds </li></ul><ul><li>Formula unit: smallest ratio of ions that forms an ionic bonded compound </li></ul><ul><li>Lattice energy: energy released when one mole of gaseous ions forms a mole of ionic crystal lattice </li></ul><ul><li>Dissociate: breaking of bonds </li></ul><ul><li>Conductivity: ability to transmit electrical charge </li></ul>
  11. 11. Ionic Solid:
  12. 12. What about  between .3 and 1.7? <ul><li>Polar covalent bonds </li></ul><ul><li>Uneven sharing results in charged ends of molecules </li></ul><ul><li>Water is an example of a polar covalent molecule. The charged ends of the molecule make water sticky, give it a high boiling point, and are the reason snowflakes are shaped the way they are </li></ul>
  13. 13. FYI: clarification! (not on the test!) <ul><li>Look at the electronegativity difference between boron and fluorine to predict the bond type in BF 3 . </li></ul><ul><li>Predictions based on this “rule” say this should be an ionic compound, but in the lab, it has been determined that this bond is actually very polar covalent. </li></ul><ul><li>The diagram on the left of page 176 is instructive. This suggests the  is actually not a fixed rule with a LINE to separate that .3 and 1.7, but rather a “shades of gray” (or blue and green!) situation. </li></ul><ul><li>Conclusion? This is a guideline, but the lab is the only way to definitively establish bond type. </li></ul>
  14. 14. Intermolecular attractions between particles <ul><li>Dipole-Dipole forces: occur between polar molecules </li></ul><ul><li>Hydrogen bonding: a type of dipole-dipole force in which a hydrogen atom in a polar bond is attracted to the electronegative end of another polar molecule </li></ul><ul><li>London dispersion forces: instantaneous tiny dipoles created in collisions between non-polar molecules or noble gas atoms </li></ul>
  15. 15. Comparing ionic and covalent bonds <ul><li>Ionic bonds dissociate in solution </li></ul><ul><li>Ionic substances conduct when in solution or molten </li></ul><ul><li>Covalent bonds are stronger than ionic bonds </li></ul><ul><li>Covalent substances melt and boil at LOWER temperatures than ionic. WHY? </li></ul>
  16. 16. Polyatomic ions <ul><li>A group of covalently bonded atoms working together as a single ion </li></ul><ul><li>Example: the hydroxide ion, OH - </li></ul><ul><li>The oxygen and hydrogen are covalently bonded, but together have 10 electrons and 9 protons, for a net charge of -1. They stick together, bonding as a single ion in compounds like KOH, an ionic compound. KOH dissociates into K + and OH - in solution. </li></ul><ul><li>See chart on window wall for more polyatomic ions. </li></ul>
  17. 17. Metallic Bond
  18. 18. Metallic bonds <ul><li>Vocabulary: Sea of electrons </li></ul><ul><li>How do the properties of metals result from the metallic bond? </li></ul><ul><li>We usually don’t contrast metallic bonds with ionic and covalent; they could be generally considered a subgroup of covalent bonds due to their  , but they don’t form molecules. They’re just different. Be aware of them, but the ionic/covalent differences are of greater importance. </li></ul>