Electronegativity
Ionic covalent continuum

When chlorine and hydrogen react the
covalently bonded HCL is made

When chlorine and sodium react ionicly
bonded NaCl is formed

Why does Cl share electrons with H yet
remove electrons from Na?
Why does Cl share electrons with H
yet remove electrons from Na?

Hydrogen holds its electrons really tightly in
H-H gas

Sodium is a metal the doesn’t hold it’s
valance electrons as tightly

Chemists use the term electronegativity
Electronegativity
What is it?
• Electronegativity is the power of an
atom to attract electron density
in a covalent bond
Remember the above definition …
Or in layman's terms
the “attractiveness” of an atom to
electrons in a bond
Electronegativity
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
Electronegativity
Pauling’s electronegativity scale
Electronegativity
Pauling’s electronegativity scale
F
Electronegativity
Pauling’s electronegativity scale
F
4.0
Electronegativity
Pauling’s electronegativity scale
Li
1.0
F
4.0
Electronegativity
Pauling’s electronegativity scale
Li
1.0
Be
1.5
F
4.0
Electronegativity
Pauling’s electronegativity scale
Li
1.0
Be
1.5
B
2.0
F
4.0
Electronegativity
Pauling’s electronegativity scale
Li
1.0
Be
1.5
B
2.0
C
2.5
F
4.0
Electronegativity
Pauling’s electronegativity scale
Li
1.0
Be
1.5
B
2.0
C
2.5
N
3.0
F
4.0
Electronegativity
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
Electronegativity
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
Electronegativity
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
Electronegativity
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
Electronegativity
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
-
So what does all this mean?
Same atoms bonding
= same electronegativity
= pure covalent bond
 Different atoms bonding
=different electronegativity
= Polar covalent or Ionic bond
Confused? How do we tell which one?
Difference in electronegativity
Covalent and ionic are a opposite ends of the
same scale

Ionic Bond
Polar
Covalent
Covalent
If the difference in
electronegativities is between:
1.7 to 4.0 = Ionic Bond
0.3 to 1.7 = Polar Covalent
0.0 to 0.3 = Non-Polar Covalent