1. Section 12.1 Characteristics of Chemical Bonds 1.To understand why atoms form bonds 2.To learn about ionic and covalent bonds and explain how they are formed. 3.Define a polar covalent bond Objectives

2. Section 12.1 Characteristics of Chemical Bonds Ch. 12 Chemical Bonding - Preview 1.When representing a water molecule as H--O--H, what do the lines between the letters represent? 2.Write the electron configurations for Fluorine, Neon, and Sodium Bonds, attractive forces F1s 2 2s 2 2p 5 Ne 1s 2 2s 2 2p 6 Na 1s 2 2s 2 2p 6 3s 1

3. Section 12.1 Characteristics of Chemical Bonds Why do atoms form bonds? What happens when two atoms get close together? What is a chemical bond? An electrical attraction between nuclei and valence electrons of different atoms. A bond represents the minimum potential energy for two atoms.

4. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Bond – an attractive force (electrostatic) between atoms. Bond energy – energy stored in chemical bonds; measured as the energy needed to break a bond; describes the strength of a bond.

5. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Ionic compound results when a metal reacts with a nonmetal Transfer of electrons from one atom to another Force between oppositely charged ions Ionic Bonding (a) (b)

6. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds A covalent bond results when electrons are shared two atoms Covalent Bonding

7. Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds A polar covalent bond results when electrons are shared unequally Covalent Bonding –One atom attracts the electrons more than the other atom

8. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself –Increases from left to right across a period –Decreases down a group of representative elements

9. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity The polarity of a bond depends on the difference between the electronegativity values of the atoms forming the bond

10. Section 12.1 Characteristics of Chemical Bonds Electronegativity

11. Section 12.1 Characteristics of Chemical Bonds Electronegativity Electronegativity Difference Bond Type < 0.4Nonpolar covalent 0.4 < x < 1.9Polar covalent > 1.9ionic

12. Section 12.1 Characteristics of Chemical Bonds B. Electronegativity

13. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge

14. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments Water molecule dipole moment

15. Section 12.1 Characteristics of Chemical Bonds C. Bond Polarity and Dipole Moments The polarity of water affects its properties –Causes water to remain liquid at higher temperature –Permits ionic compounds to dissolve in it