Polarity & Lewis Structures

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

Polarity 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

Examples H—Cl H—C H—H H—O S—Cl Ca and Cl C and S Mg and F N and O   H—H H—O S—Cl Ca and Cl C and S Mg and F N and O O and H S and O

Lewis Structure- Covalent Bonds Shows how valence electrons (v.e.) are shared in a molecule

Types of Covalent Bonds Single Bond- 2 ve- Double Bond – 4 ve- Triple Bond- 6 ve-

Octet Rule All atoms want 8 ve- EXCEPT: H- 2ve- and B- 6ve- There are other exceptions such as S and P

How to draw Lewis Structure Step 1 Determine the total number of valence electrons Ex. NF3

Step 2 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 3 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 4 Check and make sure all atoms follow the octet rule If not, put in multiple bonds

Ionic Bonds Shows the transfer of electrons

Determining Lewis Structure 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