Covalent Bonding
Polar Bonds and Molecules
Covalent Bonding
-- Polar Bonds and Molecules -Bond Polarity
• “The Tug of War”
– The pairs of electrons that are bonds between atoms are pulled
between the nuclei of the atoms in a bond.
– The electronegativities of the atoms determine the winner.
• Classifications for Bonds
– Nonpolar covalent
• When atoms pull the bond equally
• Happens with two atoms of equal electronegativity, most often
using the same atoms
• Examples: H2, O2, N2
– Polar covalent
• When atoms pull the bond unequally
• Happens with two atoms of different electronegativities
• Example: HCl, HF, NH
Covalent Bonding
-- Polar Bonds and Molecules -Bond Polarity
•
•
In a polar molecule, one end of the molecule is slightly more electronegative
than the other atom, resulting in one atom being slightly negative (-) because
of higher electronegativitiy, and the other atom being slightly positive (+)
because of lower electronegativity.
 is known as a partial charge since it is much less than 1+ or 1- charge.
Covalent Bonding
-- Polar Bonds and Molecules -Bond Polarity
• Electronegativities and Bond Types
– H: 2.1 Cl: 3.0 Since hydrogen is less, it will have the positive
partial charge while chlorine has the negative partial charge.
– 3.0 – 2.1 = 0.9 HCl is polar covalent.
0.0 – 0.1 difference
Nonpolar covalent bond
H – H (0.0 difference)
0.1 – 1.7 difference
Polar covalent bond
H – Cl (0.9 difference)
1.7 + difference
Ionic bond
Na+Cl- (2.1 difference)
Covalent Bonding
-- Polar Bonds and Molecules -Polar Molecules
•
•
Dipole
– Molecule that has two poles
– Example: HCl from the previous page
Polar vs. Nonpolar
H2O and CO2
Both have 3 atoms; yet,
One is polar and one is
nonpolar.
Why?
Structure (with bond
polarity) determines the
molecules polarity.
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