Essential Question: What are polar bonds and polar molecules? TOPIC: BOND Polarity and Molecule Polarity

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)

Classification of Bonds You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements The bigger the electronegativity difference the more polar the bond. Type of Bond Electronegativity Difference Nonpolar Covalent 0  0.4 Polar Covalent 0.5  2.4 Ionic Above 2.4

Practice Your Turn To Practice What type of bond is HCl? (H = 2.1, Cl = 3.1) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond. Your Turn To Practice N(3.0) and H(2.1) H(2.1) and H(2.1) Ca(1.0) and Cl(3.0) Al(1.5) and Cl(3.0) Mg(1.2) and O(3.5) H(2.1) and F(4.0)

How to show a bond that is polar It is NOT a whole charge just a partial charge d+ means a partially positive (less electronegative) d- means a partially negative (more electronegative) * The Cl pulls harder on the electrons The electrons spend more time near the Cl d+ d- H Cl

Polar Molecules Molecules with a positive and a negative end Requires two things to be true 1.) The molecule must contain polar bonds This can be determined from differences in electronegativity. 2.) Asymmetric molecule.

Symmetrical Molecules Because of symmetry, molecules that have polar bonds are overall a nonpolar molecules (+ and – charges cancel out or balance out) Examples: CO2 BF3 CCl4

Asymmetrical Molecules If a molecule has polar bonds (and there is no symmetry to cancel out + and – charges), the molecule is polar. Examples: H2O HCl NH3

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

Practice Drawing Dipoles P- Br P = 2.1 Br = 2.8 P –Br + - Practice H(2.1) – S(2.5) F(4.0) - C(2.5) C(2.5) - Si(1.8) N(3.0) – O(3.5)

Is it Polar? HF H2O NH3 CF4 CO2

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.