Chemical Bonding

1. Chemical Bonding Chem I: Chapters 4, 5, 9 Chem IH: 7, 8, 9

2. Unit 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. • Explain how interparticle forces affect the properties of ionic & covalent compounds.

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. The Chemical Bond • The force that holds two atoms together • Occurs using valence electrons

14. Lewis Dot Diagram Definition: System of showing the valence e-s for an atom Help us predict bonds

15. Lewis Dot Diagram, cont. 1) Element symbol in middle 2) Valence e-s represented by dots • Place v.e.-s around the element symbol in 4 locations • Above • Below • Left • Right • Don’t pair up any, until 1 in each location.

16. Lewis Dot Diagram, cont. Practice: Together: let’s do LDD for Hydrogen, helium, You practice: lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon.

17. Lewis Dot Diagram of Main Group Elements

18. The Noble Gases All occur in nature BUT no compounds containing them are ever found in nature Common denominator is that they all have 8 valence e-s. (*except He, which has 2) This is what makes them stable/unreactive This is called “Noble Gas Configuration” (NGC)

19. All “Other” Elements All other elements “want” NGC, so they can be stable.

20. Atoms can Get NGC in one of 2 ways (cont.) 1. Lose/gain e-s (IONIC bond) • This occurs when the 2 atoms in the bond pull on their e-s w/different strengths • Big EN difference • Typically occurs btwn a _____ & a _____.

21. Atoms can Get NGC in one of 2 ways (cont.) 2. Share e-s (COVALENT bond) • This occurs when the 2 atoms in the bond pull on their e-s w/the same (or similar) strength • Small EN difference • Typically occurs between 2 ___________.

22. 3 “Classes” of Elements(Review- Do Not Copy) • 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”

23. Ions & the Octet Rule Ions are charged particles that have lost or gained e-s to satisfy the octet rule (8 e-s) They will typically form based on what requires the smallest gain or loss of e-s to complete an octet. Ex: Na  Na+ + e- Ex: Cl + e-  Cl-

24. Formation of Ions The charge on an ion is called its “oxidation number”

25. Formation of Ions, cont. • Metals tend to lose electrons • Have + oxidation number • Called “cations” • Metal ions are given the element name • Ex: Na+ = “sodium ion”

26. Formation of Ions, cont. • Nonmetals tend to gain electrons • Have – oxidation number • Called “anions” • Nonmetal ions are given the element name w/an “-ide” ending • Ex: O2- = “oxide ion”

27. TO DO: Label Your Periodic Table • Label Groups 1, 2, 3, 16, 17 w/the oxidation number of each group. Group #Oxidation # 1 +1 2 +2 3 +3 16 -2 17 -1

28. Practice Together, write the arrow orbital diagram for a sodium atom. Now draw the arrow orbital diagram for a sodium ion. Identify the noble gas that has the same notation as a sodium ion. Write the symbol for a sodium ion

29. Formation of an ionic bond • When e-s are lost by 1 atom they are gained by another. Therefore, cations & anions are formed at the same time. • Occur between elements w/great differences in EN. • Usually a metal & a nonmetal • Ex: Na & Cl

30. Formation of an ionic bond, cont. Attraction between ions is what forms bond. Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Cl-1 Na+1 Practice: Draw Lewis Dot Diagrams for sodium and chlorine ATOMS. Then show what happens to form sodium & chlorine IONS. (BONUS: What NG is each ion like?)

31. Formation of an ionic bond, cont. • Note: you will not always have a 1:1 ratio of + to - ions. • Ex: MgI2 -see next slide

32. Formation of MgI2 .. .. • .Mg. + :I: → Mg.+ + :I: - (are they happy?) . .. .. .. .. .. • .Mg. + :I: :I: → Mg2+ + :I: - :I:- . . .. ..

33. ACTIVITY: Egg Carton AtomsIonic Bonding MATERIALS • Egg carton (“atom”) • Candy or marbles (“electrons”) • Data Sheet

34. 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.

35. 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.

36. 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?)

37. 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.

38. Step 3: Discuss Results

39. Now it’s your turn! • Partner 1: 3 e-s • Partner 2: 9 e-s • (Identify your elements first.) • With your new set of “electrons,” form an ionic compound with your partner. • Record your data and your partner’s. • Be prepared to discuss.

40. Results of Example 2: Li & F

41. 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)

42. “Isoelectronic” • Term used to describe atoms/ions with the same e- 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

43. Formulas • Tell us: • the elements that make up the compound • the # of atoms of each element in a unit of the compound • The smallest unit of an Ionic Compound is called a “Formula Unit” • The smallest unit of a Covalent compound is called a Formula Unit or “Molecule”

44. 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)

45. Crystal Arrangement Causes Behavior of Ionic Compounds e Fig 22-25 p 570 • Each ion is “locked in” in 6 directions (ex: each Na+ is surrounded by 6 Cl-) • Giant Ionic Lattice • Rotating NaCl Lattice

46. Properties of Ionic Compounds • Brittle • Cubic in shape • Very stable • Solids (high MP, BP.) • Very soluble in water • Electrolyte

47. Ionic Compounds-Electrolytes • 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!

48. Interparticle Forces • The attraction between formula units (particles of a substance) is called: “INTERPARTICLE FORCES” • strong IP forces between adjacent NaCl units, for example. • weak attraction between adjacent molecules of covalent compounds, H2O, for example.

49. Interparticle Forces in Covalent Compounds • Molecules have little to no charge so they are attracted v. weakly to one another • This makes covalent compounds • Liquids/gases (almost always!) • Have low MP/BP

50. Interparticle Forces in Covalent Compounds, cont. • Not soluble in water (or very slightly) ex: oil, gas, CO2 • poor conductors-WHY??? Think-Pair-Share!!!