1. Chapter 4: Chemical Bonding When Atoms Collide

2. Today’s Objectives To be able to: Explain why some elements react (form bonds.) Explain why some elements react (form bonds.) Explain the difference between an ionic & a covalent bond. Explain the difference between an ionic & a covalent bond. Demonstrate e- reconfiguration when a simple compound is formed. Demonstrate e- reconfiguration when a simple compound is formed.

3. Sodium (metal)  Solid  Good conductor of electricity & heat  VERY reactive  Silvery/luster  Malleable, soft  Melting point-low 98 C  Uses: never pure in nature b/c sooooo reactive!

4. Chlorine (nonmetal)  Poisonous, green gas  Disinfectant  Reactivity-very reactive. Rarely found pure in nature b/c sooo reactive.

5. Salt (NaCl)  Edible, common food additive  White  Crystalline solid  Reactivity-not reactive/ very stable  Brittle  Conductivity- as a solid, poor conductor  As a liquid or in aqueous solution, excellent conductor = ELECTROLYTE

6. Carbon (nonmetal)  Solid @ room temperature  Fairly unreactive @ rm temperature. Very reactive at high temperatures.  Most of the compounds in living things made from carbon.  Brittle/hard (charcoal/diamond)  High melting & boiling points

7. Oxygen (Nonmetal)  Gas at room temp  Colorless, odorless, tasteless  21% of atmosphere  Very low MP/BP (-183 C BP)  Slightly soluble in water  Reactive, combines w/many elements  Most abundant element in earth’s crust

8. Carbon dioxide  Somewhat soluble in water  Poor conductor  Fairly unreactive  Uses  some fire extinguisher b/c it won’t burn  Photosynthesis  Nearly all the food for all living things comes thru photosynthesis  Trees pull CO 2 out of the air & decrease greenhouse effect

9. Hydrogen  Odorless, tasteless, colorless  Very reactive (ex: Hindenburg)  Low MP & BP  Gas at rm temperature  Slightly soluble in water  not a conductor  Lightest and most abundant element in universe

10. Water  Liquid at room temp  Stable-doesn’t react w/most things  examples  Chemical rxns in human body take place in water  `Necessary for photosynthesis

11. Classwork On p 59 of I.N.  Analyze CO2  Compare the properties of C, O, and CO2

12. What is Happening?  Watch the videos.  What is happening in all of these reactions ? Hydrogen balloon burning 2H 2 + O 2  2H 2 O sodium metal & chlorine Na + Cl  NaCl sodium iodide & mercury (II) chloride 2NaI + HgCl 2  2NaCl + HgI 2

13. When Atoms Combine to Form Compounds

16. Stable “Happy” Atoms  Have Noble Gas Configuration (NGC)  8 valence electrons  OR 2 valence electrons if only the 1st energy level is occupied (Like He)

17. ACTIVITY: Egg Carton Atoms Ionic Bonding MATERIALS Egg carton (“atom”) Egg carton (“atom”) Candy or marbles (“electrons”) Candy or marbles (“electrons”) Data Sheet Data Sheet

18. Rules for “Placing” e-s  Place e-s in lowest available E.L.  Fill an E.L. before putting e-s in next available E.L.  Only 1 “electron” per space in egg carton.

19. Your Goal:”Happy” Atoms Ionic Compound With your partner, obtain NGC for BOTH of your atoms!  Each atom will have EITHER  A full 1st E.L. & no e-s in 2nd E.L. OR  A full 1st and 2nd E.L.  One will donate e-s & one will receive e-s.

21. Step 1: Your Atom  Count # of “e-s”  Identify element  Identify column/group#  What is valence level?  How many valence e-s?  How many e-s must be gained to obtain NGC?  How many e-s must be lost to obtain NGC?  How many e-s lost or gained (Which is easier?)

22. Step 2: Both Atoms  Share your information with your partner & record on Data Table.  Decide how you can help each other obtain NGC by giving or receiving e-s.  Make the e- switch! & observe NGC.

23. Step 3: Discuss Results

24. Now it’s your turn!  With your new set of “electrons,” form an ionic compound with your partner.  Record your data and your partner’s.  Be prepared to discuss.

25. Results of Example 2: Li & O

26. So what about the bond?  When e-s are lost or gained, the atom develops a charge and becomes an ion.  Attraction between ions is what forms bond.  Note: you will not always have a 1:1 ratio of + to - ions.  Ex: MgI2-see next slide

27. Formation of MgI2........ .Mg. +:I: → Mg. + :I: (are they happy?)................... .Mg. +:I: :I: → Mg + :I: :I:......

28. 3 “Classes” of Elements  Metals = pink Conductors? Yes! Hold e-s? Loosely How many V.E’s? 1-3  Nonmetals = green Conductors? No! Hold e-s? Tightly How many V.E.’s? 5-7  Metalloids = blue “In between”

29. Ionic Bonding  Typically occurs between a metal (“weak”) & a nonmetal (“strong”)  Metal loses e-s, forming a + ion (cation)  Nonmetal gains e-s, forming a - ion (anion)

30. Covalent Bonding  Involves the sharing of electrons.  Occurs when the 2 atoms involved are close in “strength” (pull on e-s)  Usually occurs between  2 nonmetals

31. Activity: Egg Carton Atoms Covalent Bonding Your Goal: With your partner, obtain NGC for both your atoms by sharing electrons! NOTE: Overlap cartons to represent sharing of e-s.

32. Practice Together: H 2  Each partner is going to represent a H atom.  Let’s answer the Qs together.

33. Step 2: Both Atoms  Remove “e-s” from rows that will be overlapped.  Overlap 1 carton’s row/s with your partner’s.  Place the removed e-s from both atoms in the overlapped rows. -NGC!

34. Step 1: Your Atom, F  Count # of “e-s”  Identify element  Identify column/group#  What is valence level?  How many valence e-s?  How many e-s must be gained to obtain NGC?  This is the # of rows that must be overlapped to share e-s with your partner.

35. Step 2: Both Atoms  Remove “e-s” from rows that will be overlapped.  Overlap 1 carton’s row/s with your partner’s.  Place the removed e-s from both atoms in the overlapped rows. -NGC!

36. Solution

37. More Practice  Each person makes their atom.  Next form covalent compound with neighbor.  Oxygen  Nitrogen

38. Answers to practice  Oxygen involves the overlap of 2 rows in each carton. (double bond)  Nitrogen involves the overlap of 3 rows in each carton. (triple bond)

39. Quiz  Ionic bonds are formed by the ______ of electrons.  Covalent bonds are formed by the ________ of electrons.  CO is a/n ionic/covalent compound.  NaF is a/n ionic/covalent compound.

40. Summary so Far  Atoms that collide may bond if they can help each other become more stable.  Noble gases are stable the way they are-8 valence e-s in most cases (“octet”).  All other elements want to be like noble gases.  Two ways to get “NGC”  Transfer e-s if strength of 2 elements is very unequal (ionic bond)  Share e-s if strength of 2 elements is pretty equal (covalent bond)

41. “Isoelectronic”  Term used to describe atoms/ions with the same electron configuration  Ex: F- and Ne  Both have 2 e-s in the 1 st energy level  Both have 8 electrons in the 2 nd energy level  Ex: He and H-  Both have 2 electrons in the exact same arrangement

42. Formulas  Tells  the elements that make up the compound  the # of atoms of each element in a unit of the compound  “Formula Unit” v. Molecule  Formula Unit applies to all compounds  Molecule applies ONLY TO COVALENT COMPOUNDS

43. To Explain Why…  Elements in an ionic compound occur in a specific ratio, BUT  You never have just 1 Na and 1 Cl, for example  Instead YOU HAVE A CRYSTALLINE STRUCTURE (“lattice”) (see p 134)

44. Crystal Arrangement Causes Behavior of Ionic Compounds  Each ion is “locked in”  This makes ionic compounds  Very stable  Solids (high MP, BP.)  Brittle  Cubic in shape The attraction between formula units (particles of a substance) is called: “INTERPARTICLE FORCES” In addition, ionic compounds are  Very soluble in water  good conductors of electricity-WHY??? e Fig 22-25 p 570

45. Ionic Compounds-Good Conductors  In order for something to be a good conductor, it must have freely moving charged particles.  Ions are charged particles that are “locked in” when in solid form…  BUT when they are melted or dissolved in water, BOY CAN THEY MOVE!

46. Interparticle Forces in Covalent Compounds  Molecules are attracted weakly to one another  This makes covalent compounds  Liquids/gases (almost always!)  Have low MP/BP In addition, Covalent compounds are  Not soluble in water (or very slightly)  poor conductors-WHY??? Think-Pair-Share!!!

47. Why covalent compounds are lousy conductors.  In order for something to be a conductor, it must have freely-moving charged particles.  Molecules carry little to no charge. Therefore, they cannot conduct electricity well. TOO BAD!

48. Types of Covalent Bonds  Single Bond- When a pair of electrons is shared  Double Bond….you tell me!  Triple Bond…