Polar Bonds Chemistry Mr. Scott

So Let’s Review… Two types of bonds that we’ve discussed… 1. Covalent 2. Ionic

Electronegativity The measure of the ability of an atom in a bond to attract electrons Increases from left to right on the periodic table and from bottom to top

Covalent Bonds Occur between two nonmetals Electronegativity of the two elements is very close Electrons are shared equally

Ionic Bonds Occur between a metal and a nonmetal Cation (positive ion) and the anion (negative ion) have electronegativities that are very far apart Electrons are “stolen” by the anion

But not all sharing is equal… What happens when two nonmetals have electronegativities that are somewhere in between? The atom with the higher electronegativity will have the electron more than the atom with the lower electronegativity.

And these bonds are called… POLAR BONDS Polar bonds have a slightly positive atom (lower electronegativity) and a slightly negative atom (higher electronegativity) But they’re not quite ions! This is called a dipole

Lower Probability Density Higher Probability Density

Polar Molecules If the entire molecule has a slightly positive end and a slightly negative end then we call it a polar molecule. Ex: H2O, HCl

And that’s why water works! The interaction of the dipoles is what actually holds water together! The slight negatives (Oxygen) are attracted to the slight positives (Hydrogens) These are called hydrogen bonds

And oil separates because… Nonpolar molecules don’t interact with the charges of the dipoles, therefore the water and nonpolar molecules separate. And that’s how cell membranes work!

http://www.college-cram.com/study/chemistry/presentations/603

Quick Recap… How are polar and nonpolar covalent compounds similar? How are they different? What is a dipole? What is a hydrogen bond? Why don’t oil and water mix?