Covalent Bonding and Polarity

What is polarity? Focus on covalent bonds

Contributes to the properties of chemical compounds

Based on electronegativity difference between atoms within chemical bonds

Chose your polarity 1) Nonpolar Covalent

small to same electronegativity difference Occurs among same or similar atoms bonded together EQUAL sharing of electrons, equal distribution of

electron density

2) Polar Covalent difference in electronegativity Most electronegative atom pulls electrons towards it UNEQUAL sharing of electrons, electron density

displaced toward electronegative atom

Polar Covalent Bonds

Example 1: Arrange the following

bonds in order of DECREASING polarity. Br—Cl H--Cl Cl—Cl I--Cl Cl--F

Partial Charges Exist in polar covalent molecules

Demonstrates tendency of one end to be “slightly” negative or positive

NO charge on the whole molecule

Example 1: H2O

Example 2: HCl

Example 3: PH3

Formal Charges Difference between # of valence electrons present

in an atom NOT in chemical bond and # of valence electrons present in an atom WITH a chemical bond

Not actual charges in covalent molecule Neutral molecules = 0 formal charge Polyatomic/charged molecule = net charge

Valence Electrons in atom involved in chemical bond Lone-pair electrons around atom ½ electrons in a chemical bond

Formal Charges (cont.)

Formal Charge =

#valence electrons in free atom - #lone pair electrons around bound atom – ½ (# of electrons present in bond with atom)

Example 1: Which Lewis structure is

more likely???

Resonance Some molecules or ions have more than one possible

Lewis Structure

Structures ONLY vary in electron distribution

Resonance hybrid A mix/hybrid of all possible Lewis structures True molecule/ion structure

**Draw all resonance structures and connect with double arrow—resonance hybrid is a blend **

Resonance (cont.) Delocalized Electrons

Electrons are not restricted to where they can “hang out”

Electrons distribute among several atoms Seen with resonance as electron distribution varies

Localized Electrons Electron distribution does NOT vary Electrons stay in a specific region between atoms No resonance

Example 1: Draw 3 Lewis structures for SO3 and

describe how the resonance hybrid relates to all 3.

Example 2: Draw 3 Lewis structures for NO3

- and describe how the resonance hybrid relates to all 3.

Homework Read pp. 351-353, 357-360

Problems pp. 381-382, #41, 42, 45, 46, 47, 49, and 51