Chemical Bonds

Gilbert Newton Lewis (surrounded by pairs of electrons)

Practice Lewis Dot Lewis suggested a means of keeping track of outer (or valence) electrons Na O Mg Al I

Overview: Types of Bonds There are 2 bond types : ionic and covalent In ionic bonding one atom has a stronger attraction for electrons than the other, and “steals” an electron from a second atom In covalent bonding the attraction for electrons is similar for two atoms. They share their electrons to obtain an octet. MgO(ionic),CaCl 2 (ionic),SO 2 (covalent), PbCl 2 (ionic),CCl 4 (covalent),CH 4 (covalent)

Cl – Na + Cl – Ionic bonding Ionic bonding involves 3 steps (3 energies) 1) loss of an electron(s) by one element, 2) gain of electron(s) by a second element, 3) attraction between positive and negative Na Cl e–e– 1) 2) 3) Na +

When is the bond Ionic? Metal and non-metal (alkali & Halogens) Electronegativity Difference The rule is that when the electronegativity difference is greater than 1.7, the bond is ionic.

HOW TO DO An Ionic Bond Step 1 find out valence electrons for each Element. Draw diagram (Lewis Dot Diagram) Show the transfer Write the answer without the electron dots

Ionic bonding (Q5 - Li + Cl) Ionic bonding (stealing/transfer of electrons) Li Cl Li + Cl  Li+Cl–

Ionic bonding: Mg + O Mg + O  Mg 2+ O 2– O Mg

Ionic bonding: Al + 3 Cl

COVALENT BONDS Step 1 find out valence electrons for each Element. Draw diagram (Lewis Dot Diagram) Connect the Dots Draw the circles to show sharing of electrons Draw the bond structure using symbols and Lines Write the answer without the electron dots

F2F2

CS 2

NH 3

BF 3 (Hard) CFl 3 (Harder) CFl 3 (Harder) CH 2 F 2 (Hardest) CH 2 F 2 (Hardest) CH 3 COOH (Challenge)