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Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
Attractions Between Particles
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Attractions Between Particles

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  • 1. Attractions between Particles Chapter 6, Holt Modern Chemistry Lisa Allen
  • 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. Useful sites <ul><li>http://www.visionlearning.com/library/module_viewer.php?mid=55 </li></ul><ul><li>http://www.chemtutor.com/compoun.htm </li></ul>
  • 4. Covalent bonds <ul><li>Occurs between atoms of similar electronegativity (  &lt;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. Covalent molecules
  • 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. Ionic bonds <ul><li>Occurs between atoms of very different electronegativity (  &gt;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. Ionic humor?
  • 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. 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. Ionic Solid: http://web.jjay.cuny.edu/~acarpi/NSC/salt.htm
  • 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. 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. 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. 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. 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. Metallic Bond
  • 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>

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