1. Bell Work  Turn In Big Idea #2 Practice  Pick Up Note Sheets

2. Bonding Chemical Bond – electrostatic force that holds atoms together  Goal is lowest energy conformation possible (stability)  Energy of the grouping is lower than the energy of the separated atoms  Focus is on  Bond Properties  Bond Energy

3. Valence electrons Bonding involves the highest energy level (valence) e- Valence e- can be represented with Lewis Dot Diagrams # of valence electrons matches with main group #

4. Valence electrons

5. Ionic : metal & nonmetal Covalent: nonmetals only Transfer e- to get octet Share e- to get octet

6. Electrostatic attraction = EMF Ionic Bond Covalent Bond Cation  Anion Nucleus  Shared e- Which Type Of Bond Is Stronger? Why? Which Type Of Bond Is Stronger? Why?

7. Electronegativity Depends on size and atomic number (charge of nucleus) Trends  More protons = Stronger ENC = Smaller radius Electronegativity increases towards Fluorine Why Are The Nobel Gases Not Shown?

8. Bond character Terminology is character NOT strength, bond determines properties Very few substances are purely covalent or purely ionic Would Water Be More Covalent Or More Ionic? Why? Would Water Be More Covalent Or More Ionic? Why?

9. Ionic bonding Electron(s) Transfer  Smaller Cation & Larger Anion Electrostatic Attraction Occurs  Bond Forms Crystal Lattice Occurs  Compound Is Made WHY? Energy levels… Shielding e-… Valence e-… ENC… WHY? Energy levels… Shielding e-… Valence e-… ENC… Forming Ions is Ionization energy & electron affinity Endo = energy added = + Exo = energy released = - Which is which? Forming Ions is Ionization energy & electron affinity Endo = energy added = + Exo = energy released = - Which is which?

10. Crystal structure Surround By Opposite ions Shape is based on ion sizes & mole ratio (X 2 Y, XY 3, etc.) Electrostatic Attraction In Multiple Directions Strength depends on distance (size) & charge (ratio) …Coulomb’s BOND LENGTH

11. Bond strength = Lattice Energy Lattice Energy: energy needed to separate ions Columb’s Law k = constant proportionality constant Q1, Q2 = charges on the ions r = distance between the centers of each ion NaF or MgO Which has greater bond strength? Why! NaF or MgO Which has greater bond strength? Why!

12. Characteristics of Ionic Compounds o Crystalline solids at room temperature o Brittle o High melting points & boiling points Increase as lattice energy increases o Soluble in water o Conduct - only as liquids or solutions

13. Concept Application Would the boiling point of NaCl be a ) Lower than NaF b) Larger than MgO c) Between NaF and MgO Provide justification based on concepts

14. Intermission = Take 5

15. Occurs between atoms with similar electronegativities (nonmetals, metalloids, atoms in a polyatomic ion) Covalent Bonding

16. Shared e- are simultaneously electrostatically attracted to two nuclei Orbitals overlap, atoms are held together as a group making an individual molecule Shared e- go between the two nuclei, balance the repulsion, lower the overall energy

17. Electrons will form pairs  Lone pair: e- belong to just one atom  Bonding pair: e- are shared between two atoms Bonding pairs = a bonds (electrostatic attractions) Lewis Structures

18. Lewis structures STEPS / RULES: 1. Sum up the valence e- from all atoms and charges from ions PCl 3 valence e- = 5 + (3 x 7) = 26 2. Write symbols for atoms and connect them with a single bond (subtract 2e- from the available valence FOR EACH BOND) each bond is 2e- keep track of e-: 26  6 = 20

19. 3. Complete octet rule around all the atoms except the central atom (the least atoms of, the least EN) 4. Use leftover e- to give the central atom an octet, if there are not enough e- to make an octet, try multiple bonds Lewis structures keep track of e-: 20 – 18 = 2

20. Lewis Diagram Examples Missing octet

21.  H only gets 2e-  B and Be often have less than 8 e- BF 3 = 24e –  3 rd period and down can exceed octet rule by using empty d orbital AsBr 5 = 40e- Lewis Structures exceptions

22. Your Turn Make a Lewis Diagram For Carbon Dioxide Molecule, CO 2 Sulfate Ion, SO 4 2-

23. e- in reality can move around the entire molecule More than one valid Lewis structure / bond position can exist Resonances shown by using a double headed arrow Resonance HCO 2 – = 18e –

24. Formal Charge  Common form is more stable, has the lowest formal charges VE = valence e- NE = nonbonding e- (lone) BE = bonding e- (shared) CO 2 with double bonds Is more stable CO 2 with double bonds Is more stable

25. more bonding e- = less repulsion o Atoms are closer o Bond length is shorter more bonding e- = more attraction o Bond strength increase o Bond movement decreases Bond Properties

26. Coulombs law: charge & distance More shared e- Shorter bond length = strength More charge = strength Coulomb’s Still At Play HOW?

27. Sigma (σ) = Single Orbitals overlap “head to head” e- meet between atoms center Pi (  ) = Double & Triple Orbitals meet “side to side” e- meet above and below atoms center Also contain a sigma bond Double Bond = sigma & pi Triple Bond = sigma & 2 pi Bond Properties

28. Bond Order Bond order = number of bonds

29. Electronegativity determines level of attraction for shared e- Similar values (0.0 - 0.4) = equal sharing = nonpolar bond Bond Properties – Polarity

30. Differing Values (0.5 – 2.0) = unequal sharing = polar bond Creates unequal distribution of e- in the molecule Bond Properties – Polarity

31. Molecule is neutral (no e- lost or gained) Uneven distribution creates areas of slight charge (dipoles) One side is Slightly positive Slightly negative Distribution gradually changes, forming a dipole moment And polar covalent molecule Bond Properties – Polarity

32. Bond properties

33. Homework Finish Chap 8 Reading Lab Report