Polar Molecular Compounds SWBAT: Identify Polar and Nonpolar Molecules

Periodic Table Trends Atomic Radii  Half the distance between the nuclei of two adjacent atoms Electronegativity  Ability of an atom to attract electrons when bonded with another atom

Atomic Radii Trend

Electronegativity Trend  Electronegativity is highest within the nonmetals with Fluorine having the highest. Why are noble gases excluded?

Electronegativity Trend

A.Three Types of Bonds: non-polar, polar, ionic Use Electronegativity (EN) values to determine type of bond EN value: H = 2.1 C = 2.5 N = 3.0 O = 3.5 F = 4.0 P = 2.1 S = 2.5 Cl = 3.0 Br = 2.8 I = 2.5  Every element has a specific EN value  We will focus on the elements of organic chemistry C,H,N,O,P,S and Halogens  Do not need to memorize

Electronegativity Difference and type of bond

Rating of Covalent Bonds:  Example 1: What type of bond is H-Cl?  EN: H = 2.1 Cl: 3.0  Subtract ENs from each other, larger – smaller  3.0 – 2.1 = 0.9 compare to rating  Redraw compound with partial charges: δ+ & δ- δ+ δ- H – Cl Dipole Moment = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic *Polar Covalent = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic

Rating of Covalent Bonds:  Example 1: What type of bond is H-Br?  EN: H = 2.1 Br: 2.8  Subtract ENs from each other, larger – smaller  2.8 – 2.1 = 0.7 compare to rating  Redraw compound with partial charges: δ+ & δ- δ+ δ- H – Br Dipole Moment = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic *Polar Covalent = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic

Rating of Covalent Bonds:  Example 2: What type of bond is C-H?  EN: H = 2.1 C: 2.5  Subtract ENs from each other, larger – smaller  2.5 – 2.1 = 0.4 compare to rating  Less than 0.5 = no partial charges, no dipole arrow C – H = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic *Nonpolar Covalent = nonpolar.5 – 1.7 = polar 1.8 and greater = ionic

Tips  Bonds between different elements always have some kind of dipole moment regardless of polarity rating  Draw the dipole arrow of Br – Pd (use just their position in the PT) Br – Pd  Bonds between same elements never have a dipole moment regardless of individual EN  No dipole between F – F or H – H

Practice Problems  Using electronegativity difference, classify each bond as ionic, polar covalent, or nonpolar covalent.  Show the partial charge for any polar covalent bonds.  K – F EN values: K = 0.8 & F = 4.0  O – O EN values: O = 3.5  I – Cl EN values: I = 2.5, & Cl = 3.0

Practice Problems  Using electronegativity difference, classify each bond as ionic, polar covalent, or nonpolar covalent.  Show the partial charge for any polar covalent bonds.  K – F EN values: K = 0.8 & F = 4.0  = ionic bond  O – O EN values: O = 3.5  = 0 - nonpolar covalent bond  I – Cl EN values: I = 2.5 & Cl = 3.0  = polar covalent bond δ+ δ- I – Cl

Practice Problems  The bonds between the following pairs of elements are covalent. Arrange them according to polarity, listing the most polar first. a. H – Cl b. H – C c. H – F d. H – O e. H – H f. S – Cl

Homework Problems  4.50 Describe the end in EN going down a group.  4.52 Approximately what EN difference would you expect for a polar covalent bond?  4.54 Predict whether each of the following bonds is ionic, polar covalent or nonpolar covalent:  A. Si-O B. K-Cl C. S-F D. P-Br E. Li-O F. N-P  4.56 For each of the following bonds, indicate the positive end with δ+ and the negative end with δ-. Write an arrow to show the dipole for each.  A. Si-Br B. Se-F C. Br-F D. N-H E. N-P