1. 1 Announcements & Agenda (01/26/07) You should finish reading Ch 4 and start Ch 5 over the weekend. Quiz today! Today (4.1-4.3, 4.5): Ionic vs. covalent bonding & the Octet Rule Ionic vs. covalent bonding & the Octet Rule Ionic and covalent compounds Ionic and covalent compounds Naming and writing ionic compounds Naming and writing ionic compounds

2. 2 Last time: Electrons in Energy Levels Energy Orbitals Maximum Total Level (Shell) No. of Electrons Electrons 1 1s 22 2 2s 28 2p 6 2p 6 3 3s 218 3p 6 3p 6 3d 10 3d 10 4 4s 232 4p 6 4p 6 4d 10 4d 10 4f 14 4f 14 How do we know orbitals exist??? Spectroscopy

3. 3 Last Time: Periodic Law All the elements in a group have the same electron configuration in their outermost shells Outermost electrons are called valence electrons Elements with same # of valence electrons display similar chemical & physical properties!!! Example: Group 2 Be2, 2 Mg 2, 8, 2 Mg 2, 8, 2 Ca 2, 2, 8, 2

4. 4 Last time: Metals, Nonmetals, & Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left.Metals are located to the left. Nonmetals are located to the right.Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals.Metalloids are located along the heavy zigzag line between the metals and nonmetals. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

5. 5 Last Time: More Periodic Trends How Atomic Orbital filling affects: Atomic Size (Radius) Atomic Size (Radius) Ionization Energy Ionization Energy n Definitions…. Ionization Energy : Cost of removing an e - from a neutral atom Ionization Energy : Cost of removing an e - from a neutral atom Atomic Radii: Distance between center of nucleus and outer electron shell

6. 6 30 Good Practice Problems (Ch 4) 4.01, 4.05, 4.07, 4.09, 4.11, 4.13, 4.15, 4.17, 4.23, 4.25, 4.35, 4.37, 4.41, 4.45, 4.47, 4.49, 4.53, 4.55, 4.57, 4.59, 4.63, 4.65, 4.67, 4.69, 4.85, 4.87, 4.93, 4.97, 4.103, and 4.105

7. 7 Chemical Bonds Attraction between two or more atoms Attraction between two or more atoms Interaction between valence electrons Interaction between valence electrons Ionic bonds Ionic bonds Covalent bonds Covalent bonds

8. 8 An amazing thing about the universe - It works in a way that sometimes when things come together, they stick… Protons and neutrons in a atomic nuclei Atoms in molecules H H H Bonding Overview

9. 9 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’) Chemical Bonds: attractive force holding two or more atoms together

10. 10 Guiding Principle: 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?

11. 11 Reminder: Valence Electrons Electrons in the highest (outer) electron level Electrons in the highest (outer) electron level Have most contact with other atoms Have most contact with other atoms Known as valence electrons Known as valence electrons Outer shells of noble gases contain 8 valence electrons (except He = 2) Outer shells of noble gases contain 8 valence electrons (except He = 2) Example: Ne 2, 8 Ar2, 8, 8

12. 12 Electron Dot Structures Symbols of atoms with dots to represent the valence- shell electrons 1A 2A 3A 4A 5A 6A 7A 8A H  He:                       Li  Be   B   C   N   O  : F  : Ne :                                       Na  Mg   Al   Si   P   S  : Cl  : Ar :                

13. 13 X : would be the electron dot formula for: 1.Na 2.Mg 3.Al 12345

14. 14 would be the electron dot formula for: would be the electron dot formula for: 1.B 2.C 3.N X 12345

15. 15 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. Charged Atoms: Ions

16. 16 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?

17. 17 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

18. 18 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- )

19. 19 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

20. 20 Formation of a Sodium Ion, Na + Sodium achieves an octet by losing its 1 valence electron. 2, 8, 12, 8 By the way, cations are always smaller than their neutral counterparts!

21. 21 Formation of a Chloride, Cl - Chlorine achieves an octet by adding an electron to its valence electrons. 2, 8, 72, 8, 8 By the way, anions are always bigger than their neutral counterparts!

22. 22 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.

23. 23 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.

24. 24 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

25. 25 The formula of the ionic compound of Na + and O 2- is 1.NaO 2.Na 2 O 3.NaO 2 12345

26. 26 The formula of a compound of calcium and sulfur is: 1.Ca 2 S 2.CaS 2 3.CaS 12345

27. 27 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

28. 28 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

29. 29 Flowchart for Naming Ionic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

30. 30 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).

31. 31 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

32. 32 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: In covalent compounds, nitrogen needs to form 3 bonds to obtain its octet!!!

33. 33 Lewis Structures: Covalent Bonds in NH 3 Bonding pairs Bonding pairs H     H : N : H     Lone pair of electrons DO LEWIS STRUCTURE ON BOARD

34. 34 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.