Electronegativity Calculations Polarity Percent Ionic
ADVERTISEMENT
1Electronegativity
Electronegativity
δ
δ
+
–
Electronegativity
Electronegativity
• Electronegativity describes
how electrons are shared in a
compound
• Consider the compound HCl
δ
δ
δ
δ
H
Cl
+
–
0
0
• The electron clouds represent where the
two electrons in the HCl bond spend their
time (sizes of atoms are not being shown)
• The shared electrons spend more time
around Cl than H. In other words Cl is
H Cl
H H
more electronegative than H.
Electronegativity
table
Answers
Electronegativity
table
Answers
• The relative attraction for electrons is
summarized in figure 7.11 (pg. 255)
• These numbers are derived from several
factors including EA, IE, ENC, atomic radius
• You do not need to understand where the
numbers come from
• You need to know that a high number means
the element has a greater pull on electrons
• You will also need to calculate the difference
between values to estimate the % ionic or %
covalent character of a bond
• PE 12 (pg. 256). Reference: 7.10.
Calculating EN differences
Defining polarity
Calculating EN differences
Defining polarity
• The first step in defining the polarity of a
• For our purposes we will define polarity in the
bond is to calculate electronegativity
following fashion: 0-10 % is non-polar, 10-
difference (Δ EN)
50% is polar (covalent), 50%+ is ionic
• Δ EN = EN large - EN small
• This is a crude estimate. In reality, the only
• E.g. for NaCl, Δ EN = 2.9 - 1.0 = 1.9
non-polar bond between 2 atoms occurs in
: Δ EN = 3.5 - 3.5 = 0)
• Next, estimate from fig 7.12 the % ionic
diatomic molecules (O
2
character: about 65% (60 - 70%)
Q - what is the polarity of the bonds in MgO,
Q-Give the % ionic character for MgO, CH, HCl
CH, HCl?
MgO =
CH =
HCl =
Note if % ionic is 20%, then % covalent is 80%
Polarity in molecules
Polarity in molecules:
Examles
Polarity in molecules
Polarity in molecules:
Examles
• A bond that you calculate to be polar may not
+
NH
NH
BrCl
3
4
be polar if the molecule is symmetrical
• Imagine a tug-of-war between atoms of the
Lewis
same strength around a central atom
Structure
• The pull in one direction is the bond polarity
or “bond dipole”. The overall/molecular
polarity is also known as “dipole moment”
ΔEN of bonds
• If the pull is the same from all directions then
Bond polarity
the electrons are not attracted to one atom
Symmetrical
over another and the molecule is non-polar
molecule?
• Read 7.11 (bottom of 256 - 259) including
Polarity
the examples. Complete the worksheet.
ADVERTISEMENT
0 votes
Related Articles
Related forms
Related Categories
Parent category: Miscellaneous