1. Chemical Bonding How Atoms Stick Together

2. Why do atoms bond? • To obtain a stable octet of valence electrons • Why do you think Noble Gases don’t form bonds?

3. Types of Bonding: Two ways to get a Stable Octet Ionic Covalent • Electrons are transferred • Found in ionic compounds • Large difference in electronegativity • What happens? An atom that can become stable by losing electrons transfers electrons to an atom that can become stable by gaining them • Electrons are shared • Found in molecular compounds • Low difference in electronegativity • What happens? Two atoms who both need to gain electrons to become stable pool their electrons together and share some of them

4. Ionic Bonding Electrons transfer from one an atom to another giving both atoms a stable octet Notice how both sodium and chlorine have 8 valence electrons in the end

5. Covalent bonding Both hydrogen and oxygen fill their valence levels by sharing electrons Were any new electrons made in the chemical reaction? Why does hydrogen only need two valence electrons to be stable?

6. How do you decide if it will be ionic or covalent? It depends on electronegativity If two atoms have a big difference in electronegativity then an ionic bond will form because the atom with the higher electronegativity will pull harder on the electrons than the one with the lower electronegativity If electronegativity difference is low than both atoms pull about the same on the electrons and sharing occurs A covalent bond is called polar if the sharing is unequal

7. Determingelectronegatvitity You can look up electronegativities of common elements on page 194 of your text

8. What type of bonds would you expect the following pairs of atoms to form? • H with O? • Na with Br • N with N • N with H • C with H • HW: read 166 to 175 and do section review on page 175

9. Lewis Structures display valence electrons as dots

10. Ionic Bonds- Lewis Structures Dots are used to represent valence electrons Notice how this shows an electron transfering from sodium to chlorine

11. Covalent bonds and dot diagrams

12. Lewis diagram of methane

13. Lewis Structures can be written with lines representing covalent bonds