Chapter 4: Chemical Bonding

1. Chapter 4: Chemical Bonding When Atoms Collide

2. Today’s Objectives To be able to: • Explain why some elements react (form bonds.) • Explain the difference between an ionic & a covalent bond. • 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 CO2 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 2H2 + O2 2H2O sodium metal & chlorine Na + Cl  NaCl sodium iodide & mercury (II) chloride 2NaI + HgCl2 2NaCl + HgI2

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 AtomsIonic Bonding MATERIALS • Egg carton (“atom”) • Candy or marbles (“electrons”) • 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” AtomsIonic 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 AtomsCovalent 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: H2 • 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. 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. Quiz

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 1st energy level • Both have 8 electrons in the 2nd 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 e Fig 22-25 p 570 • 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???

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…