Aim: What are polar bonds and polar molecules?

Polar and Nonpolar Bonds There are two types of covalent bonds Nonpolar Covalent Bonds (equal share of electrons) Polar Covalent Bonds (unequal share of electrons)

Polar Covalent Bond A Polar Covalent Bond is unequal sharing of electrons between two atoms (H-Cl) In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge

Nonpolar Covalent Bond A Nonpolar Covalent Bond is an equal sharing of electrons between two atoms (Cl-Cl, N-N, O-O)

Dipole When there is unequal sharing of electrons a dipole exists Dipole is a molecule that has two poles or regions with opposite charges A dipole is represented by a dipole arrow pointing towards the more negative end

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.

solutions water 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).

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? F2 the 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

Summary In a polar bond, one atom is more electronegative than the other. In a nonpolar bond, both atoms have similar electronegativities. An asymmetric molecule with polar bonds is a polar molecule. An asymmetric molecule with nonpolar bonds is a nonpolar molecule. A symmetric molecule, regardless of the polarity of the bonds, is always a nonpolar molecule.