Transcript Rating of Covalent Bonds

Polar Molecular
Compounds
SWBAT: Identify Polar and
Nonpolar Molecules
Periodic Table Trends
Atomic Radii
 Half
the distance
between the nuclei
of two adjacent
atoms
Electronegativity
 Ability
of an atom
to attract electrons
when bonded with
another atom
Atomic Radii Trend
Atomic Radii Trend
Electronegativity Trend
 Electronegativity
is highest within the
nonmetals with Fluorine having the
highest. Why are noble gases excluded?
Electronegativity Trend
A. Three Types of Bonds:
non-polar, polar, ionic
Use Electronegativity (EN) values to
determine type of bond
EN value:
H = 2.1 C = 2.5 N = 3.0 O = 3.5 F = 4.0
P = 2.1 S = 2.5 Cl = 3.0
Br = 2.8
I = 2.5
Every element has a specific EN value
We will focus on the elements of organic
chemistry C,H,N,O,P,S and Halogens
Do not need to memorize
Electronegativity Difference
and type of bond
Rating of Covalent Bonds:
 Example
1: What type of bond is H-Cl?
 EN: H = 2.1 Cl: 3.0
 Subtract ENs from each other, larger – smaller
 3.0 – 2.1 = 0.9 compare to rating
 Redraw compound with partial charges: δ+ & δδ+ δ-
H – Cl
Dipole Moment
*Polar Covalent
0 - .4 = nonpolar
.5 – 1.7 = polar
1.8 and greater = ionic
Rating of Covalent Bonds:
 Example
1: What type of bond is H-Br?
 EN: H = 2.1 Br: 2.8
 Subtract ENs from each other, larger – smaller
 2.8 – 2.1 = 0.7 compare to rating
 Redraw compound with partial charges: δ+ & δδ+ δ-
H – Br
Dipole Moment
*Polar Covalent
0 - .4 = nonpolar
.5 – 1.7 = polar
1.8 and greater = ionic
Rating of Covalent Bonds:
 Example
2: What type of bond is C-H?
 EN: H = 2.1 C: 2.5
 Subtract ENs from each other, larger – smaller
 2.5 – 2.1 = 0.4 compare to rating
 Less than 0.5 = no partial charges, no dipole arrow
C–H
0 - .4 = nonpolar
.5 – 1.7 = polar
1.8 and greater = ionic
*Nonpolar Covalent
Tips
 Bonds
between different elements always
have some kind of dipole moment
regardless of polarity rating
 Draw the dipole arrow of Br – Pd (use just
their position in the PT)
Br – Pd
 Bonds between same elements never
have a dipole moment regardless of
individual EN
 No
dipole between F – F or H – H
Practice Problems
 Using
electronegativity difference, classify
each bond as ionic, polar covalent, or
nonpolar covalent.

K
Show the partial charge for any polar
covalent bonds.
– F EN values: K = 0.8 & F = 4.0
 O – O EN values: O = 3.5
 I – Cl EN values: I = 2.5, & Cl = 3.0
Practice Problems
 Using
electronegativity difference, classify
each bond as ionic, polar covalent, or
nonpolar covalent.
Show the partial charge for any polar
covalent bonds.

K
– F EN values: K = 0.8 & F = 4.0

O

I
4.0 - 0.8 = 3.2 - ionic bond
– O EN values: O = 3.5
3.5 - 3.5 = 0 - nonpolar covalent bond
– Cl EN values: I = 2.5 & Cl = 3.0

3.0 - 2.5 = 0.5 - polar covalent bond
δ+
δ-
I – Cl
Practice Problems
 The
bonds between the following pairs of
elements are covalent. Arrange them
according to polarity, listing the most
polar first.
a. H – Cl
b. H – C
c. H – F
d. H – O
e. H – H
f. S – Cl
Homework Problems
 4.50
Describe the end in EN going down a group.
 4.52 Approximately what EN difference would
you expect for a polar covalent bond?
 4.54 Predict whether each of the following bonds
is ionic, polar covalent or nonpolar covalent:

A. Si-O
B. K-Cl
C. S-F
D. P-Br
E. Li-O
 4.56
F. N-P
For each of the following bonds, indicate the
positive end with δ+ and the negative end with
δ-. Write an arrow to show the dipole for each.

A. Si-Br
B. Se-F
C. Br-F
D. N-H
E. N-P