D. W.as a high

school student

It’s another

WEINERPOINTPRESENTATION

PART III

Polar

Bonds

We know aCOVALENT bondcomes from sharing thebonding pair of electrons

F FShared pair

(bonding pair)

F FThe nucleus of each atompulls on the bonding pair.

F FBoth atoms have equal pull,

so the bonding pair is shared equally.

H ClIf two different atoms share a bond,

one will pull more stronglyon the bonding electrons.

H Cl

H Cl

H Cl

H Cl

H Cl

H Cl

H Cl

H Cl

H ClThe bonding electrons carry negative charge.

H ClThe closer they get to the chlorine atom,

the more negative it gets.The farther they get from the hydrogen,

the more positive it gets.

H Cl+

_

But the charge is only partial.Hydrogen has not lost the electronsas in the formation of an ion.

H ClThere is an unequal sharing of electrons.

H ClThe partial charge is denoted by a + or – and the Greek letter delta,

–+

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

–+

–+

A polar bond is a bond in which thebonding electron pair is shared unequally.

A polar molecule is a moleculewith regions of partial negative (–)

and partial positive (+) charge.

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

W h at is e lec tro n eg a tiv ity ??

Two atoms of equal electronegativitywill share the bond equally

F F

H ClTwo atoms with a small difference in electronegativity will share unequally,

resulting in partial charge.

3.02.1

H ClTwo atoms with a small difference in electronegativity will share unequally,

resulting in partial charge.

–+

H ClThis is a polar bond:

The bonding pair is, on average,closer to one atom.

–+

H Cl–+

Is a p o la r b o n d a co v a len t b o n d ?

FKTwo atoms with a large difference in electronegativity will result in a loss

of an electron,resulting in a full charge.

4.00.8

FK

FK

FK

FK

FK

FK

+ _

FKpositive ion negative ion

A polar bond in a moleculemay make the entire moleculepolar, with one end slightlypositive and the other endslightly negative.

Hydrogen chloride is an exampleof a polar molecule.

H Cl–+

The SHAPE of the moleculedetermines whether its polar

bonds make the molecule polar

In CF4 the fluorines are symmetricallyarranged around the carbon.

The fluorines all pull on the valenceelectrons in opposite directions,

effectively cancelling out the polarityof the bonds

CF4 has four polar bondsbut it is a non-polar molecule:There is no partial charge

on the molecule.

The two hydrogens of water arenot symmetrically positioned

around the oxygen.

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

–+

+

Water is a liquid instead of a gasbecause the partial positives and negatives

attract each other.

+

–

+ –

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

+

–

+ –