Electronegativity and Polarity Chemistry. A Strange Observation… AlCl 3 – Aluminum Chloride Is...
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Transcript of Electronegativity and Polarity Chemistry. A Strange Observation… AlCl 3 – Aluminum Chloride Is...
![Page 1: Electronegativity and Polarity Chemistry. A Strange Observation… AlCl 3 – Aluminum Chloride Is this an ionic or a covalent compound? How can we tell?](https://reader031.fdocuments.us/reader031/viewer/2022013101/56649f295503460f94c4253c/html5/thumbnails/1.jpg)
Electronegativity and Polarity
Chemistry
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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?
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Don’t Believe Everything You Hear…
• Remember when we thought covalent bonds were so nice…
• Turns out, some of them aren’t so nice…
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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-
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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
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Electronegativity
What 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
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ElectronegativityPauling’s electronegativity scale
F
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ElectronegativityPauling’s electronegativity scale
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
B2.0
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
B2.0
C2.5
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
B2.0
C2.5
N3.0
F4.0
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ElectronegativityPauling’s electronegativity scale
Li1.0
Be1.5
B2.0
C2.5
N3.0
O3.5
F4.0
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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
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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
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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
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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-
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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
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H FIf two different atoms share a bond,
one will pull more stronglyon the bonding electrons.
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H F
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H F
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H F
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H F
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H F
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H F
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H F
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H F
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H FThe bonding electrons carry negative
charge.
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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.
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H F+
_
But the charge is only partial.Hydrogen has not lost the electronsas in the formation of an ion.
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H FThere is an unequal sharing of electrons.
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H FThe partial charge is denoted by a + or – and the Greek letter delta, d
d – d +
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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.
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The degree of sharing (equal to unequal)is determined by the electronegativitydifference between the two atoms.
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F FShared pair
(bonding pair)
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F FWhat is the electronegativity of each atom?
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F FBoth atoms have equal pull,
so the bonding pair is shared equally.
Non-polar covalent bond
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Example:Determine the type of bond in hydrogen chloride.DEN = |ENH – ENCl|
= |2.1 - 3.0|
DEN = 0.9
Polar covalent bond
d+ d-
Rule:Lower EN d+Higher EN d-
H Cld+d-
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Example:Determine the type of bond in water.
DEN = |ENH – ENO|
= |2.1 - 3.5|
DEN = 1.4
Polar covalent bond
d+ d-
Rule:Lower EN d+Higher EN d-
d+d-H O
H
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Example:Determine the type of bond in ammonia.
DEN = |ENN – ENH|
= |3.0 - 2.1|
DEN = 0.9
Polar covalent bond
d+d-
Rule:Lower EN d+Higher EN d-
d+d-N
HH
H
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Example:Determine the type of bond in methane.
DEN = |ENC – ENH|
= |2.5 - 2.1|
DEN = 0.4
Nonpolar covalent bond
C
HH
H
H
No shift of e-No polesNo charges