Topic 1 - Matter and Energy - Revsworld

Topic 4 .– Chemical Bonding
25. Degree of bond and molecular polarity: Using electronegativity difference
Bond polarity refers to how ionic, polar, or covalent is a bond between two atoms.
Molecular polarity refers to how polar is a molecule of a substance.
A compound may contain a bond that has more ionic or more covalent characteristics than a bond
between atoms of another compound. Some molecules also have more polar characteristics than
others do. The degree of bond and molecular polarity of substances depends largely on the
electronegativity difference between the two atoms in the formula of the substance.
RECALL: Electronegativity measures atoms ability to attract (pull) electron from another atom during
chemical bonding.
To calculate electronegativity difference between two atoms in a bond:
Step 1 : Get electronegativity values for both elements in the formula (Use Reference Table S)
Step 2: Calculate electronegativity difference
Electronegativity difference = High electronegativity – Low electronegativity
To determine which formula is most or least ionic or polar:
Consider the scale below.
Electronegativity Difference scale ranging from 0 - 4
0 -------------------------------------------1.7--------------------------------------------------> 4
Least polar
As Electronegativity Difference increases
Most polar
Least ionic
Polarity and ionic characteristics increase
Most ionic
Most covalent Covalent characteristic decreases
Least covalent
According to above scale:
The smaller the difference in electronegativity, the more covalent, the less ionic and the less
polar the substance.
The larger the difference in electronegativity, the less covalent, the more ionic, and the more
polar the substance.
26. Degree of bond and molecular polarity. Determining which formula is most or least ionic or polar
Concept Task: Be able to determine which formula is most or least ionic, covalent or polar.
To determine:
Most ionic, Most polar, or Least Covalent: LOOK for Highest electronegativity difference :
Least Ionic, Least polar, or Most Covalent : LOOK for Lowest electronegativity difference :
Below, three formulas are given. The formula with most and least are chosen based on the
electronegativity difference. Study this example to learn to do the same.
Given the formulas: LiCl KCl FrCl
Cl = 3.2 Cl = 3.2 Cl = 3.2
Get electronegativity values for the
elements (Use Table S)
Li = 1.0 K = 0.8 Fr = 0.7
Do electronegativity difference 2.2 2.4 2.5
NOTE Lowest and highest difference ( Lowest difference) (Highest difference)
LiCl : Least ionic
FrCl : Most ionic
Determine most and least Least polar Most polar
based on differences Most covalent Least covalent
Copyright © 2011 E3 Scholastic Publishing. All Rights Reserved. 85