Covalent Bonding

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


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.


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)


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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Covalent Bonding