Electronegativity and Polarity
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Transcript of Electronegativity and Polarity
A Strange Observation…• AlCl3 – Aluminum Chloride• Is this an ionic or a covalent compound?• How can we tell?
• Despite consisting of a metal and a non-metal, aluminum chloride is actually a covalent compound…
• WHAT GIVES?
Don’t Believe Everything You Hear…
• Remember when we thought covalent bonds were so nice…
• Turns out, some of them aren’t so nice…
Reality Sets In…• Covalent bonds fall into two
categories depending on how the electrons are shared between the atoms.
• Polar covalent – unequal sharing of e-• Nonpolar covalent – equal sharing of
e-
So How Do You Tell the Difference?
I can tell you!!!
Really – just because I look crazy doesn’t mean I don’t know
my crap – use ELECTRONEGATIVITY
Your new boy – Linus Pauling
ElectronegativityWhat is it?Electronegativity is the measure of
an atom’s ability to attract electrons unto itself in a covalent bond
The higher the value, the more electronegative the element
ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
B2.0
C2.5
N3.0
O3.5
F4.0
Na0.9
Mg1.2
Al1.5
Si1.8
P2.1
S2.5
Cl3.0
ElectronegativityPauling’s electronegativity scale
H He
Li1.0
Be1.5
B2.0
C2.5
N3.0
O3.5
F4.0
Ne
Na0.9
Mg1.2
Al1.5
Si1.8
P2.1
S2.5
Cl3.0
Ar
ElectronegativityPauling’s electronegativity scale
H2.1
He
Li1.0
Be1.5
B2.0
C2.5
N3.0
O3.5
F4.0
Ne
Na0.9
Mg1.2
Al1.5
Si1.8
P2.1
S2.5
Cl3.0
Ar
ElectronegativityPauling’s electronegativity scale
H2.1
He-
Li1.0
Be1.5
B2.0
C2.5
N3.0
O3.5
F4.0
Ne-
Na0.9
Mg1.2
Al1.5
Si1.8
P2.1
S2.5
Cl3.0
Ar-
The following chart may be used to determine the type of bond in a compound.
Electronegativity Type of Type ofDifference Bond Sharing
0.0 – 0.4 Nonpolar Equal0.5 - 1.9 Polar Unequal>1.9 Ionic None, transfer
H FThe closer they get to the fluorine atom,
the more negative it gets.The farther they get from the hydrogen,
the more positive it gets.
H F+
_
But the charge is only partial.Hydrogen has not lost the electronsas in the formation of an ion.
A polar bond is a bond in which thebonding electron pair is shared unequally.
A polar molecule is a moleculewith regions of partial negative (d –)
and partial positive (d +) charge.
The degree of sharing (equal to unequal)is determined by the electronegativitydifference between the two atoms.
Example:Determine the type of bond in hydrogen chloride.DEN = |ENH – ENCl|
= |2.1 - 3.0|
DEN = 0.9Polar covalent bond
d+ d-
Rule:Lower EN d+Higher EN d-
H Cld+d-
Example:Determine the type of bond in water.DEN = |ENH – ENO|
= |2.1 - 3.5|
DEN = 1.4Polar covalent bond
d+ d-
Rule:Lower EN d+Higher EN d-
d+ d-H O
H
Example:Determine the type of bond in ammonia.DEN = |ENN – ENH|
= |3.0 - 2.1|
DEN = 0.9Polar covalent bond
d+d-
Rule:Lower EN d+Higher EN d-
d+d-N
HH
H