Polar Molecular Compounds SWBAT: Identify Polar and Nonpolar Molecules

Polar Molecular CompoundsSWBAT: 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

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 bondEN 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 valueWe will focus on the elements of organic chemistry C,H,N,O,P,S and HalogensDo not need to memorize

Electronegativity Differenceand 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

0 - .4 = nonpolar.5 – 1.7 = polar1.8 and greater = ionic

*Polar Covalent



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


*Polar Covalent



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 Covalent


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

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

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

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

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Polar Molecular Compounds SWBAT: Identify Polar and Nonpolar Molecules