8.5 electronegativity and polarity closer to it when it's in...

8.5 Electronegativity and Polarity

Electronegativity is the tendency of an atom to draw electronscloser to it when it's in a chemical bond.

If the rope in the picture represents electrons, the atom with the higher electronegativity will win the tug-of-war match for electrons.

Electronegativity increases as you move up and to the right on the periodic table towards F.

The type of bond formed during a reaction is related to an atom's attraction for electrons.

There are three types of bonds:1. Nonpolar covalent: equal sharing of electrons

between 2 atoms in a bond2. Polar covalent: uneven sharing. Electrons in the

bond hang out with the more electronegative element.

3. Ionic: The more electronegative atom is so strong, it steals the electron.

100

% co

vale

nt10

0%

ionic

Bonds between 2 different atoms are never completely ionic or covalent, but a mixture of the 2.

Finding the electronegativity difference between the two atoms in the bond determines bond character.

100

% co

vale

nt

100

%ionic

0 0.4 1.7

nonpolarcovalent

polarcovalent

mostly ionic

Electronegativity difference determines bond character:

Electronegativity and Bond Character

100

% co

vale

nt10

0%

ionic

0 0.4 1.7

nonpolarcovalent

polarcovalent

mostly ionic

Example: Hydrogen has an electronegativity of 2.1. Bromine is 2.8. The electronegativity (EN) difference between the two is 0.7.HBr is a polar covalent bond.

Notice that the electrons spend more time with Br. This end of the molecule is partially negative.

Because the electrons don't spend much time around hydrogen,this end is partially negative.

This symbol means "partial".

Because HBr has two opposite sides of polarity, it is a POLAR MOLECULE.

Polar molecules stick to their neighbors and tend to have higher boiling points.

Bonds between two identical atoms have a zero electronegativity difference. They are 100% nonpolar covalent.

Example: O2

EN difference: 3.5-3.5 = 0

Polarity and molecular shape

Molecules can have polar bonds but the molecule itself can be either polar or nonpolar.

If the molecule has an asymmetrical charge distribution, it will be polar.Water is very polar.EN difference for OH bond: 3.5-2.1 = 1.4 polar covalent

Carbon tetrachloride:EN difference for C-Cl bond:

3.0 - 2.5 = 0.5

Polar bonds but nonpolar molecule.

Be able to:a. Calculate electronegativity difference between two atoms

in a bondb. Determine bond typec. Determine bond characterd. Determine polarity of molecule

Carbon dioxide

a. 3.5 - 2.5 = 1.0b. polar covalentc. 20% covalent and 80% ionicd. Nonpolar molecule



Ammonia



Boron trichloride



Phosphorus trichloride

forces BETWEEN molecules that keep them in the solid or liquid phase.

The stronger the polarity of a molecule, the stronger theINTERMOLECULAR FORCES (IMFs)

"Like dissolves like."

Polar molecules dissolve in other polar substances but will NOT dissolve in nonpolar substances.

Oil (nonpolar) and water (polar) don't mix.

8.5 electronegativity and polarity closer to it when it's in...

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