Electronegativity and Polarity

1. Electronegativity and Polarity Chemistry

2. A Strange Observation… • AlCl3 –Aluminum Chloride • Is this an ionic or a covalent compound? • How can we tell? • Despite consisting of a metal and a non-metal, aluminum chloride is actually a covalent compound… • WHAT GIVES?

3. Don’t Believe Everything You Hear… • Remember when we thought covalent bonds were so nice… • Turns out, some of them aren’t so nice…

4. Reality Sets In… • Covalent bonds fall into two categories depending on how the electrons are shared between the atoms. • Polar covalent – unequal sharing of e- • Nonpolar covalent – equal sharing of e-

5. So How Do You Tell the Difference? I can tell you!!! Really – just because I look crazy doesn’t mean I don’t know my crap – use ELECTRONEGATIVITY Your new boy – Linus Pauling

6. Electronegativity What is it? Electronegativity is the measure of an atom’s ability to attract electrons unto itself in a covalent bond The higher the value, the more electronegative the element

7. Electronegativity Pauling’s electronegativity scale

8. Electronegativity Pauling’s electronegativity scale

9. Electronegativity Pauling’s electronegativity scale

10. Electronegativity Pauling’s electronegativity scale

11. Electronegativity Pauling’s electronegativity scale

12. Electronegativity Pauling’s electronegativity scale

13. Electronegativity Pauling’s electronegativity scale

14. Electronegativity Pauling’s electronegativity scale

15. Electronegativity Pauling’s electronegativity scale

16. Electronegativity Pauling’s electronegativity scale

17. Electronegativity Pauling’s electronegativity scale

18. Electronegativity Pauling’s electronegativity scale

19. The following chart may be used to determine the type of bond in a compound. Electronegativity Type of Type of Difference Bond Sharing 0.0 – 0.4 Nonpolar Equal 0.5 - 1.9 Polar Unequal >1.9 Ionic None, transfer

20. H F If two different atoms share a bond, one will pull more strongly on the bonding electrons.

21. H F

22. H F

23. H F

24. H F

25. H F

26. H F

27. H F

28. H F

29. H F The bonding electrons carry negative charge.

30. H F The closer they get to the fluorine atom, the more negative it gets. The farther they get from the hydrogen, the more positive it gets.

31. _ + H F But the charge is only partial. Hydrogen has not lost the electrons as in the formation of an ion.

32. H F There is an unequal sharing of electrons.

33. d + d – H F The partial charge is denoted by a + or – and the Greek letter delta, d

34. A polar bond is a bond in which the bonding electron pair is shared unequally. A polar molecule is a molecule with regions of partial negative (d –) and partial positive (d +) charge.

35. The degree of sharing (equal to unequal) is determined by the electronegativity difference between the two atoms.

36. Shared pair (bonding pair) F F

37. F F What is the electronegativity of each atom?

38. F F Both atoms have equal pull, so the bonding pair is shared equally. Non-polar covalent bond

39. Cl H Example: Determine the type of bond in hydrogen chloride. DEN = |ENH – ENCl| Rule: Lower EN d+ Higher EN d- - = | 2.1 3.0 | d- d+ d+ d- = 0.9 DEN Polar covalent bond

40. H O H Example: Determine the type of bond in water. DEN = |ENH – ENO| Rule: Lower EN d+ Higher EN d- - = | 2.1 3.5 | d- d+ = 1.4 DEN Polar covalent bond d+ d-

41. N H H H Example: Determine the type of bond in ammonia. DEN = |ENN – ENH| Rule: Lower EN d+ Higher EN d- - = | 3.0 2.1 | d- d+ = 0.9 DEN d- d+ Polar covalent bond

42. H C H H H Example: Determine the type of bond in methane. DEN = |ENC – ENH| - = | 2.5 2.1 | = 0.4 DEN Nonpolar covalent bond No shift of e- No poles No charges