1. 1 Announcements & Agenda (01/29/07) Pick up graded quizzes (Average = 8.2/10) Note: Need more detailed/precise explanations Note: Need more detailed/precise explanations This week’s quiz moved to Friday Today (4.3-4.6): More on ionic & covalent compounds More on ionic & covalent compounds Naming and writing ionic & covalent compounds Naming and writing ionic & covalent compounds Electronegativity & Bond Polarity (4.6) Electronegativity & Bond Polarity (4.6)

2. 2 An amazing thing about the universe - Sometimes when things come together, they stick… Protons and neutrons in a atomic nuclei Protons and neutrons in a atomic nuclei Atoms in molecules Atoms in molecules H H H Last Time: Bonding Overview

3. 3 TWO EXTREME CASES Ionic bonding: results when “Atom A” transfers an electron to “Atom B” (e.g. salts such as NaCl)Ionic bonding: results when “Atom A” transfers an electron to “Atom B” (e.g. salts such as NaCl) Covalent bonding: results when atoms share electronsCovalent bonding: results when atoms share electrons Polar-covalent bonding: everything in between (a good portion of ‘reality’)Polar-covalent bonding: everything in between (a good portion of ‘reality’) Last Time: Chemical Bonds: attractive force holding two or more atoms together

4. 4 Last Time: The Octet Rule An octet in the outer shell makes atoms stable An octet in the outer shell makes atoms stable Electrons are lost, gained or shared to form an octet Electrons are lost, gained or shared to form an octet Electronegativity (4.6): How tightly does an atom tend to hold on to electrons? Electronegativity (4.6): How tightly does an atom tend to hold on to electrons?

5. 5 Atoms are electronically neutral  they do not have a charge. WHY? Charge from protons and electrons cancel WHY? Charge from protons and electrons cancel But an atom can lose or gain electrons (it cannot lose or gain protons…) An ion – is a particle with an unequal number of protons and electrons. Last Time: Ions

6. 6 Ions tend to form “octets.” → Periodic Table 2 Flavors: Cations – positive charge, generally metal atoms – result from loss of 1 or more electrons. Anions – negative charge, generally nonmetals, result from gain of 1 or more electrons. Carbon and boron do not form ions Why Do Ions Form?

7. 7 Ionic Charges - Cations Group 1A form cations with +1 charge. (Na +, K +, Cs + etc…) Group 2A form cations with +2 charge. (Ba 2+, Ca 2+, Mg 2 + etc…) Metals in the middle (transition metals) can be variable positive charge

8. 8 Ionic Charges - Anions Group 7A elements tend to form anions with –1 charge. (F -, Br -, I - etc..) Group 6A elements tend to form anions with –2 charge. (O 2-, S 2- etc…) Groups 5A elements can (but rare) form –3 anions (N 3- )

9. 9 Ionic Compounds A solid that contains cations and anions in a balanced whole-number ratio is called an ionic compound. Electrons lost by the cation must equal the electrons gained by the anion Electrons lost by the cation must equal the electrons gained by the anion Usually it is between a metal & a nonmetal. Example: NaCl Important: When an ionic compound dissolves, it breaks apart into ions. Covalent compounds do not!

10. 10 Formation of a Sodium Ion, Na + Sodium achieves an octet by losing its 1 valence electron. 2, 8, 1 2, 8 By the way, cations are always smaller than their neutral counterparts!

11. 11 Formation of a Chloride, Cl - Chlorine achieves an octet by adding an electron to its valence electrons. 2, 8, 7 2, 8, 8 By the way, anions are always bigger than their neutral counterparts!

12. 12 Charge Balance for NaCl, “Salt” In NaCl, a Na atom loses its valence electron.a Na atom loses its valence electron. a Cl atom gains an electron.a Cl atom gains an electron. the symbol of the metal is written first followed by the symbol of the nonmetal.the symbol of the metal is written first followed by the symbol of the nonmetal.

13. 13 Charge Balance In MgCl 2 In MgCl 2, a Mg atom loses 2 valence electrons.a Mg atom loses 2 valence electrons. two Cl atoms each gain 1 electron.two Cl atoms each gain 1 electron. subscripts indicate the number of ions needed to give charge balance.subscripts indicate the number of ions needed to give charge balance.

14. 14 From Lab: Naming Ionic Compounds Name the metal first, then the nonmetal as -ide. Name the metal first, then the nonmetal as -ide. Use name of a metal if it can only have one fixed charge Use name of a metal if it can only have one fixed charge Groups 1A, 2A, 3A and Ag (+1), Zn (+2), and Cd (+2) Examples: NaClsodium chloride ZnI 2 zinc iodide Al 2 O 3 aluminum oxide

15. 15 The formula of the ionic compound of Na + and O 2- is 1.NaO 2.Na 2 O 3.NaO 2 12345678910111213141516171819202122232425262728293031323334353637383940 41424344454647484950

16. 16 The formula of a compound of calcium and sulfur is: 1.Ca 2 S 2.CaS 2 3.CaS 12345678910111213141516171819202122232425262728293031323334353637383940 41424344454647484950

17. 17 From Lab: Transition Metals From Lab: Transition Metals Most form 2 or more positive ions 1+ 2+ 1+ or 2+ 2+ or 3+ 1+ 2+ 1+ or 2+ 2+ or 3+ Ag + Cd 2+ Cu +, Cu 2+ Fe 2+, Fe 3+ Ag + Cd 2+ Cu +, Cu 2+ Fe 2+, Fe 3+ silver cadmium copper(I) ion iron(II) ion silver cadmium copper(I) ion iron(II) ion ion ion copper (II) ion iron(III) ion ion ion copper (II) ion iron(III) ion Zn 2+ zinc ion zinc ion

18. 18 Names of Variable Ions Use a roman number after the name of a metal that forms two or more ions Transition metals and the metals in groups 4A and 5A FeCl 3 (Fe 3+ ) iron (III) chloride CuCl (Cu + ) copper (I) chloride SnF 4 (Sn 4+ ) tin (IV) fluoride PbCl 2 (Pb 2+ )lead (II) chloride Fe 2 S 3 (Fe 3+ )iron (III) sulfide Fe 2 S 3 (Fe 3+ )iron (III) sulfide

19. 19 Flowchart for Naming Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

20. 20 Covalent Bonds Formed between atoms of groups (columns) 4A- 7A (nonmetals) Formed between atoms of groups (columns) 4A- 7A (nonmetals) How do you form octets, if neither atom particularly wants to give up electrons? How do you form octets, if neither atom particularly wants to give up electrons? Share Share Form single, double, and triple bonds to yield an octet Form single, double, and triple bonds to yield an octet Applies to bonds between H, C, N, O, S, P, Halogens (F, Cl, etc) – not metals (usually). Applies to bonds between H, C, N, O, S, P, Halogens (F, Cl, etc) – not metals (usually).

21. 21 Each electron in bonding pair has greater space available than in the unbonded individual atoms, and each gets to “feel” the positive charge of both nuclei. Covalent Bonding: Considerations

22. 22 Diatomic Molecules Gases that exist as diatomic molecules are H 2, F 2, N 2, O 2, Cl 2, Br 2, I 2 octets                  N  +  N   N ::: N   triple bond   triple bond NOTE: For nitrogen to achieve its octet, it needs to form 3 bonds!!!

23. 23 Lewis Structures: Covalent Bonds in NH 3 Bonding pairs Bonding pairs H     H : N : H     Lone pair of electrons DO LEWIS STRUCTURE ON BOARD

24. 24 Carbon forms 4 covalent bonds In a CH 4, methane, molecule a C atom shares 4 electrons to attain an octet.a C atom shares 4 electrons to attain an octet. each H shares 1 electron to become stable like helium.each H shares 1 electron to become stable like helium.

25. 25 More Examples…

26. 26 Shifting Gears: Polyatomic Ions…

27. 27 Polyatomic Ions: A Group of Covalently- bonded Atoms with an Overall Charge. KNOW THESE & Table 4.7: NH 4 + ammoniumOH - hydroxide NO 3 - nitrateNO 2 - nitrite CO 3 2- carbonate HCO 3 - hydrogen carbonate (bicarbonate)

28. 28 Some Compounds with Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

29. 29 Some Compounds with Polyatomic Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

30. 30 Naming Ternary Compounds Contain at least 3 elements Contain at least 3 elements Name the nonmetals as a polyatomic ion Name the nonmetals as a polyatomic ion Examples: Examples: NaNO 3 Sodium nitrate K 2 SO 4 Potassium sulfate Al(HCO 3 ) 3 Aluminum bicarbonate or aluminum hydrogen carbonate carbonate

31. 31 Flowchart for Naming Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

32. 32 Connecting the Extremes: In Between Ionic and Covalent Bonds (4.6) A pure covalent bond occurs only when two identical atoms are bonded: N 2 Polar Covalent Bond: Unequal sharing between two dissimilar atoms Therefore, the electrons are nearer to one of the atoms, and that atom acquires a partial negative charge (  ). Therefore, the electrons are nearer to one of the atoms, and that atom acquires a partial negative charge (  ). And consequently the other atom has a partial positive charge  And consequently the other atom has a partial positive charge 

33. 33 KEY QUESTION: How do you determine which atom has the partial negative charge and which atom has the partial positive charge?

34. 34 Electronegativity: Ability of an Element to Draw Electrons to Itself The attraction of an atom for electrons is called its electronegativity. The attraction of an atom for electrons is called its electronegativity. Can be represented with numerical values Can be represented with numerical values Larger numbers mean a greater attraction for electrons Larger numbers mean a greater attraction for electrons Fluorine has the greatest electronegativity. Fluorine has the greatest electronegativity. THE TREND TO KNOW: Elements in the upper-right corner have the greatest EN values. Elements in the lower-left corner have the smallest EN values.

35. 35 Some Electronegativity Values for Group A Elements Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Low values High values ` Electronegativity increases Electronegativity increases ` Electronegativity decreases Electronegativity decreases

36. 36 The Two Extremes Revisited… The greater the difference of the EN values, the more polar the bond! An EN difference ≥ 1.8 is considered an ionic bond.

37. 37 occur between nonmetals.occur between nonmetals. have equal or almost equal sharing of electrons.have equal or almost equal sharing of electrons. have almost no electronegativity difference (0.0 to 0.4).have almost no electronegativity difference (0.0 to 0.4). Examples: Electronegativity Electronegativity Atoms Difference Type of Bond N-N 3.0 - 3.0 = 0.0 Nonpolar covalent Cl-Br 3.0 - 2.8 = 0.2 Nonpolar covalent H-Si2.1 - 1.8 = 0.3 Nonpolar covalent Nonpolar Covalent Bonds

38. 38 occur between nonmetal atoms.occur between nonmetal atoms. have an unequal sharing of electrons.have an unequal sharing of electrons. have a moderate electronegativity difference (0.5 to 1.7).have a moderate electronegativity difference (0.5 to 1.7). Examples: Electronegativity Electronegativity Atoms DifferenceType of Bond O-Cl 3.5 - 3.0 = 0.5Polar covalent Cl-C 3.0 - 2.5 = 0.5Polar covalent O-S 3.5 - 2.5 = 1.0Polar covalent Polar Covalent Bonds

39. 39 Comparing Nonpolar & Polar Covalent Bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

40. 40 Ionic Bonds occur between metal and nonmetal ions.occur between metal and nonmetal ions. form as a result of electron transfer.form as a result of electron transfer. have a large electronegativity difference (1.8 or more).have a large electronegativity difference (1.8 or more). Examples: Electronegativity Electronegativity Atoms Difference Type of Bond Cl-K 3.0 – 0.8 = 2.2 Ionic N-Na 3.0 – 0.9 = 2.1 Ionic S-Cs2.5 – 0.7= 1.8 Ionic