ElectronegativityElectronegativity

What is it?

• Electronegativity is the power of an atom to attract electrons in a bond

Why does this matter?• Chemical reactions take place when electrons are

shuffled (moved) around between atoms!

• A chemical bond: the attraction between the electrons shared between atoms and the atoms’ protons.

• The amount of “shuffling” changes depending on the atoms involved!

•Elements with a HIGH electronegativity have a STRONG pull on electrons.

•Elements with a LOW electronegativity have a WEAK pull on electrons.

difference in electronegativity

•When two atoms bond their DIFFERENCE in electronegativity determines the bond type.

difference in electronegativity

An Ionic Bond:When one atom will win the “tug of war” and take the electrons completely. This comes from a large difference in electonegativities of atoms.

A Covalent Bond: When the electronegativity of two bonding atoms is very similar, neither atom wins the “tug of war” and the electrons are shared equally.

In a true covalent bond electrons are shared equally

IONIC COVALENT

Transfer electrons Share electrons

Between an atom of high electronegativity and an atom of low electronegativity

Between two atoms of equal or very close electronegativities

NaCl N2

•If the electronegativity difference between two bonded atoms is very high the bond is ionic.•If the electronegativity difference is very low the bond is covalent.

•What if the difference in electronegativity between the two bonded atoms is in-between?

•Hold on to that question!

•SO…..•Ionic and covalent bonds are very different, but how do we predict if a bond will be ionic or covalent?

ElectronegativityElectronegativity

Pauling’s electronegativity scale• The higher the value, the more

electronegative the element

• Fluorine is the most electronegative element• It has an electronegativity value of 4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

ElectronegativityElectronegativity

Pauling’s electronegativity scale

ElectronegativityElectronegativity

Pauling’s electronegativity scale

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

B

2.0

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

B

2.0

C

2.5

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

O

3.5

F

4.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

O

3.5

F

4.0

Na

0.9

Mg

1.2

Al

1.5

Si

1.8

P

2.1

S

2.5

Cl

3.0

ElectronegativityElectronegativity

Pauling’s electronegativity scale

H He

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

O

3.5

F

4.0

Ne

Na

0.9

Mg

1.2

Al

1.5

Si

1.8

P

2.1

S

2.5

Cl

3.0

Ar

ElectronegativityElectronegativity

Pauling’s electronegativity scale

H

2.1

He

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

O

3.5

F

4.0

Ne

Na

0.9

Mg

1.2

Al

1.5

Si

1.8

P

2.1

S

2.5

Cl

3.0

Ar

ElectronegativityElectronegativity

Pauling’s electronegativity scale

H

2.1

He

-

Li

1.0

Be

1.5

B

2.0

C

2.5

N

3.0

O

3.5

F

4.0

Ne

-

Na

0.9

Mg

1.2

Al

1.5

Si

1.8

P

2.1

S

2.5

Cl

3.0

Ar

-

• That means that the most electronegative elements are in the upper-right corner of the table.

• With only a few exceptions, electronegativity values increase as you move from left to right in any period of the periodic table. • Within any group, electronegativity values decrease as you go down the group.

0 is less than .5, so the bond is a nonpolar covalent bond!

.9 is less than 1.7, but above .5, so the bond is a polar covalent bond!

•Salt crystals are repeating patterns of positive+ and negative- ions held together by electrostatic attraction.

IONIC COMPOUNDS

COVALENT COMPOUNDS

•Biological molecules are covalently bound•Most consist of the non-metals Carbon, Oxygen, Hydrogen, and Nitrogen.