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Chapter 4: Chemical Bonding

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  1. Chapter 4: Chemical Bonding When Atoms Collide

  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 Noble Gases All of them occur in nature BUT no compounds containing them ever found in nature Analysis: they are unreactive/stable as they are Question: Why are they so stable? Data: When we look at their electron configurations, they all* have 8 valence e-s! (*except He)

  14. The Noble Gases (cont.) Something about having 8 valence e-s (or 2, if you are a small atom) makes you stable, “Happy” Called “Noble Gas Configuration”

  15. Atoms can Get NGC in one of 2 ways (cont.) 1. 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 • Typically occurs between 2 ___________.

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

  17. 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”

  18. 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.

  19. Formation of an ionic bond • When e-s are lost by 1 atom & gained by another, one atom develops a + charge (“cation”) and the other develops a – charge (anion) • 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

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

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

  22. 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.

  23. 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.

  24. 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?)

  25. 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.

  26. Step 3: Discuss Results

  27. 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.

  28. Results of Example 2: Li & F

  29. 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)

  30. “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

  31. 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”

  32. 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)

  33. 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

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

  35. 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!

  36. 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.

  37. 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

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

  39. Why covalent compounds are lousy conductors. • In order for something to be a conductor, it must have freely-moving charged particles.

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

  41. Examples of Covalent Compounds The properties of covalent compounds vary more widely than those of ionic cpds. Ex: butter, water, CO2, gasoline, candle wax, table sugar, alcohol

  42. 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.

  43. Practice Together: H2 • Each partner is going to represent a H atom. • Let’s answer the Qs together.

  44. 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!

  45. 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.

  46. 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!

  47. Solution

  48. More Practice • Each person makes their atom. • Next form covalent compound with neighbor. • Oxygen • Nitrogen