Polarity &Lewis Structures

Non-polar covalent – EN difference is 0-0.3 Polar Covalent – EN difference is 0.3-~1.7 Ionic Bonds- EN difference greater than 1.7

Bonds

δ+ or δ-

H-F bond (electronegativity-H: 2.1and F: 4.0), calculate the difference, the more electronegative atom gets the δ negative charge

Polarity

H—Cl

H—C   H—H

H—O

S—Cl

Ca and Cl

C and S

Mg and F

N and O

O and H

S and O

Examples

Shows how valence electrons (v.e.) are shared in a molecule

Lewis Structure- Covalent Bonds

Single Bond- 2 ve-

Double Bond – 4 ve-

Triple Bond- 6 ve-

Types of Covalent Bonds

All atoms want 8 ve-

◦ EXCEPT: H- 2ve- and B- 6ve-

There are other exceptions such as S and P

Octet Rule

Determine the total number of valence electrons◦ Ex. NF3

How to draw Lewis StructureStep 1

Arrange atoms◦ If there is a carbon in the molecule, carbon will be

in the center.◦ If there is no carbon then the least

electronegative atom will go in the center◦ The remaining atoms will surround the center

atom

Step 2

Bond all atoms at least once◦ Bonding is sharing one valence electron from

each atom- uses 2 valence electron

Place remaining valence electrons to go around the most electronegative atoms first to agree with octet rule, if extra v.e. put on the remaining atoms

Step 3

Check and make sure all atoms follow the octet rule

If not, put in multiple bonds

Step 4

Shows the transfer of electrons

Ionic Bonds

1st – Write out each atom in the chemical formula- Remember the subscript= the # of atoms

2nd – Draw dot structure 3rd -Remove valence electrons from metal

and give them to nonmetal using arrows 4th - Write the charges on atoms and new

dot structure

Example NaCl, MgCl2, and Na2O

Determining Lewis Structure