Polar Covalent Bonds

Polar bond -A type of covalent bond between two atoms in which electrons are shared unequally, resulting in a bond in which one atom has a slightly negative charge and the other a slightly positive charge.

In a polar molecule, the ends of the molecule (called dipoles) carry an unequal charge.

Water is polar

A polar molecule is water soluble.

In order for a solution to form with molecules, they must be either both polar

or both non-polar.

solutionswater is a polar molecule - so is alcohol. When you mix water and alcohol you see a solution with both molecules in the solution. The molecules mix together.

When you try to mix a polar and a non polar molecule what happens? They don't mix. water (a polar molecule) does not mix with oil (a non polar molecule).

To determine a molecule's polarity:

Determine each atom's electronegativity.

Electronegativity

• is defined as the ability of an atom in a particular molecule to attract electrons to itself

• (the greater the value, the greater the attractiveness for electrons)

Electronegativity is a function of:

• the atom's ionization energy (how strongly the atom holds on to its own electrons)

• the atom's electron affinity (how strongly the atom attracts other electrons)

An element with high electronegativity:

• Attract electrons from other atoms• Resist having its own electrons attracted away• Fluorine is the most electronegative element

(electronegativity = 4.0)• the least electronegative is Cesium (notice that are at diagonal corners of the periodic chart)

General trends:

• Electronegativity increases from left to right along a period

• For the representative elements (s and p block) the electronegativity decreases as you go down a group

• The transition metal group is not as predictable as far as electronegativity

Predicting the type of bond based upon electronegativity differences:• if the electronegativity difference is 0, the

bond is non-polar covalent

• If the difference in electronegativities is between 0 - 2, the bond is polar covalent

• If the difference in electronegativities is 2.0 or more, the bond is ionic

Water is polar because:

• of the differences in the electronegativity between oxygen and hydrogen.

• Oxygen is to the right on the periodic table, so Oxygen is highly negative compared to hydrogen.

Water Molecule Structure

• The oxygen attracts negative charges making the area around the oxygen much more negative than the area around the hydrogen.

• The hydrogen area (positive charges) makes the molecule bend so that the 2 hydrogen atoms in the water are on the same side, pointing away from the negative area around the oxygen.

Polar or nonpolar?

F2the electrons are shared equally between the atoms, the bond is nonpolar covalent

HF• fluorine has greater electronegativity than the

hydrogen atom.• fluorine attracts electrons away from the hydrogen • The bond is a polar covalent bond

Properties of water due to its polarity:

Properties of water due to its polarity:

• Hydrogen bonds• Cohesion• Adhesion• Capillarity• Universal solvent