1. BOND
& polarity

2. Polar
Bonds

3. Electronegativity + – H Cl
08/10/99 + –
Electronegativity describes how electrons are shared in a compound
Consider the compound HCl H Cl
The electron clouds represent where the two electrons in the HCl bond spend their time (sizes of atoms are not being shown)
The shared electrons spend more time around Cl than H. In other words Cl is more electronegative than H.

4. Electronegativity
Electronegativity is a measure of the ability of an atom in a molecule to attract electrons to itself.

5. Electronegativity + – 0 0 H Cl H H

6. Electronegativities and Bond Type
The type of bond or degree of polarity can usually be calculated by finding the difference in electronegativity of the two atoms that form the bond.

7. We know a
COVALENT bond
comes from sharing the
bonding pair of electrons

8. F F
Shared pair
(bonding pair)

9. F F
The nucleus of each atom
pulls on the bonding pair.

10. F F
Both atoms have equal pull,
so the bonding pair is shared equally.

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

12. H Cl

13. H Cl

14. H Cl

15. H Cl

16. H Cl

17. H Cl

18. H Cl

19. H Cl

20. The bonding electrons carry negative charge.Cl
The bonding electrons carry negative charge.

21. H Cl The closer they get to the chlorine atom,
the more negative it gets.
The farther they get from the hydrogen,
the more positive it gets.

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

23. H Cl
There is an unequal sharing of electrons.

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

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

26. d +
d –

27. 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.

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

30. F
Two atoms of equal electronegativity
will share the bond equally

31. resulting in partial charge.Cl
3.0
2.1
Two atoms with a small difference in electronegativity will share unequally,
resulting in partial charge.

32. resulting in partial charge.
d –
d + H Cl
Two atoms with a small difference in electronegativity will share unequally,
resulting in partial charge.

33. The bonding pair is, on average,Cl
This is a polar bond:
The bonding pair is, on average,
closer to one atom.

34. d –
d + H Cl

35. resulting in a full charge.
4.0
0.8 F K
Two atoms with a large difference in electronegativity will result in a loss
of an electron,
resulting in a full charge.

36. F K

37. F K

38. F K

39. K F

40. K F

41. K F

42. positive ion negative ion+ _ K F
positive ion negative ion

43. A polar bond in a molecule
may make the entire molecule
polar, with one end slightly
positive and the other end
slightly negative.

44. d + H Cl
d –
Hydrogen chloride is an example
of a polar molecule.

45. The SHAPE of the molecule determines whether its polar
bonds make the molecule polar

46. In CF4 the fluorines are symmetrically arranged around the carbon.

47. The fluorines all pull on the valence
electrons in opposite directions,
effectively cancelling out the polarity
of the bonds

48. There is no partial charge on the molecule.
CF4 has four polar bonds
but it is a non-polar molecule:
There is no partial charge
on the molecule.

49. not symmetrically positioned
The two hydrogens of water are
not symmetrically positioned
around the oxygen.

50. d + d – d + The O-H polarities do not cancel,
and the molecule carries a partial charge.

51. Water is a liquid instead of a gas
because the partial positives and negatives
attract each other.

52. This attraction holds the molecules together,
forming a liquid rather than the
spread out molecules of a gas.