2. Chemical Bonding

3. Recall: Electron dot diagrams are for predicting bonding Dots are written on 4 sides of the symbol a. One dot - single electron b. Two dots – electron pair  Make sure your dots are bold and pairs look paired!

4. Dot Diagram Examples: Group 1A: Alkali Metals Lithium Group 6A: ChalcogensGroup 7A: Halogens Chlorine Sulfur

5. Often shown like: Chemical bond: The force that holds two atoms together.  It will always be an electrostatic attraction between oppositely charged species. What is a bond?

6. Why do atoms bond? To increase stability, but… Bonding is not always favored What types of things confer stability?  Full or empty Valence Shells  Paired Electrons

7. Bonding Types: Ionic Covalent Metallic  We’ll overview the first 2 today, and the last later on.

8. Characterized by: Transfer of electrons. Characterized by: Transfer of electrons. 1. Atoms no longer neutral because they have lost or gained e -, now called ions. gained e -, now called ions. 2. Ionic bond: Electrostatic attraction between oppositely charged ions oppositely charged ions a. Ex: Sodium chloride is made of sodium ions and chloride ions. and chloride ions. b. Compound: 2 or more atoms chemically bonded bonded 3. Some atoms can gain or lose more than one e - IONIC BONDS

9. IONIC BONDING with SODIUM AND CHLORINE

10. Properties of Ionics: High MP/BP High MP/BP Solids at room temp. Solids at room temp. Arrange themselves into a 3-D alternating pattern called a crystal lattice Arrange themselves into a 3-D alternating pattern called a crystal lattice Most dissolve readily in water (aqueous solution) Most dissolve readily in water (aqueous solution) Conductivity: Conductivity:  Solids do not conduct  Liquids do conduct  Aqueous solutions conduct (Term: Electrolyte!)

11. Characterized by electron sharing. 1. Covalent Bond: The attraction of each nucleus for a shared pair of electrons. 2. Atoms sharing electrons form a neutral particle called a molecule.  Covalently bonded compounds are called molecular compounds. 3. No electrons are gained or lost. 4. Multiple bonds: Two pairs of electrons are shared in a double bond. Three pairs of electrons are shared in a triple bond. COVALENT BONDS

12. Examples: COVALENT HYDROGEN BOND COVALENT CHLORINE BOND

13. Properties of Covalents: Lower MP/BP Lower MP/BP Solids, liquids or gases at room temp. Solids, liquids or gases at room temp. Solids often soft & waxy Solids often soft & waxy Generally do not dissolve in water Generally do not dissolve in water Conductivity: Conductivity:  No! Not in any state of matter or in aq solution

14. Electronegativity and Bond Type

15. I’m not stealing, I’m sharing unequally  All bonds share – equally or unequally! Note:  indicates “partial charge” H2H2 HClLiCl ++ –– +– covalent (non-polar) polar covalent ionic HH H Cl [Li] + [ Cl ] –

16. Ionic or Covalent? Look at electronegativity difference (∆EN):  0 to 0.29 – Non-polar Covalent Perfect sharing of e-  0.30 to 1.69 – Polar Covalent Sharing is unequal Positive & Negative ends to the bond  1.70 and up – Ionic (Not covalent, but extremely polar!) Sharing so unequal we say transfer occurs

17. Use the periodic table that I handed out to find electronegativities:

18. Ionic, polar covalent, or nonpolar covalent? S and H  2.58-2.20=0.38  polar covalent S and Cs  2.58-0.79=1.79  ionic Cl and Ca  3.16-1.00=2.16  ionic Cl and Br  3.16-2.96  nonpolar covalent

19. A polar bond occurs when electrons are unevenly shared.  All bonds with ∆EN of 0.30 or higher are polar, regardless of whether they are ionic or covalent! POLAR AND NONPOLAR BONDS

20. Arrange in order of decreasing bond polarity: H-H, O-H, Cl-H, S-H, F-H 2.20-2.20 3.44-2.20 3.16-2.20 2.58-2.20 3.98-2.20 0 1.24 0.96 0.38 1.78 F-H > O-H > Cl-H > S-H > H-H