2. Types of

3. What is a chemical bond? zBonds are forces that hold groups of atoms together and make them function as a unit

4. What do bonds tell us? zResponsible for physical properties like mp, bp, hardness, conductivity zBond Energy- energy required to break a bond

5. Sodium Chloride zIn sol’n it is Na + and Cl - zElectrons are transferred zWhen water evaporates, aggregate to form solid NaCl

6. Why?? zThe system can achieve the lowest possible energy by behaving this way!!

7. Ionic Bonding zSodium chloride is very stablemp = 800 o C zIonic substances- when an atom that loses e - easily reacts with an atom with a high affinity for e -

8. Ionic Compound zResults when a metal reacts with a nonmetal

9. Coulomb’s Law zCan be used to calculate the energy of interaction between a pair of ions zE = 2.31 x 10 -19 Jnm(Q 1 Q 2 /r) zQ 1 and Q 2 = charge of ions zr = distance b/w ion centers

10. Such as... zCalculate the energy of interaction (kJ/mol) b/w Mg 2+ and O 2- if the distance b/w them is.205 nm (2.05 A)

11. Notice! zThe answer is negative indicating that the pair is at lower energy zYou can also find the repulsion b/w like ions, but the sign will be positive

12. Bonding b/w like atoms zLet’s look at H atoms z2 unfavorable terms (e - e - repulsion and p + p + repulsion) and 1 favorable term (e - p + attraction)

14. What conditions favor bond formation?? zWhatever causes the H atoms to achieve the lowest possible total energy zBond length = when energy is at a minimum

15. The Diagram zThe energy terms involved are the net E p that results from the attractions and repulsions among the charged particles and the E K is due to e - motion

16. The Diagram zThe zero point of energy is defined with the atoms at infinite separation

17. The Diagram zAt very short distances the energy rises steeply because of the importance of the repulsive forces when the atoms are very close together

18. The Diagram zThe bond length is the distance at which the system has minimum energy

19. Covalent Bonding zThe type of bonding encountered in H 2 and any other molecules in which electrons are shared by nuclei

20. Two extremes zIonic bonding transfers electrons zCovalent bonding atoms share electrons equally

21. The Middle Ground zPolar covalent bond- atoms unequally share electrons zResults in partial positive and partial negative charge

23. When will this happen? zElectronegativity zthe ability of an atom in a molecule to attract shared electrons to itself

24. Linus Pauling (1901-95) zUS scientist zNoble Prizes for chem and peace zmethod for determining electronegativities

25. Electroneg Values zHave been determined for almost all elements zRange is 4.0 for F to 0.7 for Cs

27. Periodic Trend? You Bet! zIncreases going left to right across a period zIncreases going up a group

28. Put in order! zBased only on positions, place the following in order of increasing electronegativity zSr, Cs, Se, O, Ba

29. Were you correct? zLeast Most z Cs<Ba<Sr<Se<O

30. Bond type relationship zElectroneg diff zZero zIntermediate zLarge z Bond Type z Covalent z Polar Coval z Ionic

31. Bond Polarity zUse tables of electroneg and calculate  for each of the following bonds and then order from most covalent to most ionic

32. Try these... zNa-Cl zLi-H zH-C zH-F zRb-O

33. The answers... zNa-Cl2.1 zLi-H1.1 zH-C0.4 zH-F1.9 zRb-O2.7

34. The Ranking... zCovalentIonic zH-C, Li-H, H-F, Na-Cl, Rb-O