Polar Molecular Compounds

1. Polar Molecular Compounds SWBAT: Identify Polar and Nonpolar Molecules

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

3. Atomic Radii Trend

4. Atomic Radii Trend

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

6. Electronegativity Trend

7. 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

8. Electronegativity Differenceand type of bond

9. 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic 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 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic *Polar Covalent

10. Rating of Covalent Bonds: 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic 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 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic *Polar Covalent

11. Rating of Covalent Bonds: 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic 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 0 - .4 = nonpolar .5 – 1.7 = polar 1.8 and greater = ionic *Nonpolar Covalent

12. 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

13. 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

14. 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 • 4.0 - 0.8 = 3.2 - ionic bond • O – O EN values: O = 3.5 • 3.5 - 3.5 = 0 - nonpolar covalent bond • I – Cl EN values: I = 2.5 & Cl = 3.0 • 3.0 - 2.5 = 0.5 - polar covalent bond δ+ δ- I – Cl

15. 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 – Fd.  H – O e.  H – H f.  S – Cl

16. 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