Section 12.1 Characteristics of Chemical Bonds 1.To learn about ionic and covalent bonds and explain how they are formed 2.To learn about the polar covalent bond 3.To understand the nature of bonds and their relationship to electronegativity 4.To understand bond polarity and how it is related to molecular polarity Objectives

Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Bond – force that holds groups of atoms together and makes them function as a unit Bond energy – energy required to break a chemical bond

Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds Ionic compound results when a metal reacts with a nonmetal Ionic Bonding (a) (b)

Section 12.1 Characteristics of Chemical Bonds A. Types of Chemical Bonds A covalent bond results when electrons are shared by nuclei Covalent Bonding

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

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

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

Section 12.1 Characteristics of Chemical Bonds B. Electronegativity

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

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

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

Section 12.2 Characteristics of Ions and Ionic Compounds 1.To learn about stable electron configurations 2.To learn to predict the formulas of ionic compounds 3.To learn about the structures of ionic compounds 4.To understand factors governing ionic size Objectives

Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions

Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions

Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions Atoms in stable compounds usually have a noble gas electron configuration –Metals lose electrons to reach noble gas configuration –Nonmetals gain electrons to reach noble gas configuration

Section 12.2 Characteristics of Ions and Ionic Compounds A. Stable Electron Configurations and Charges on Ions Chemical compounds are always electrically neutral Predicting Formulas of Ionic compounds

Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic bonding and Structures of Ionic Compounds Ions are packed together to maximize the attractions between ions Structures of Ionic Compounds

Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic bonding and Structures of Ionic Compounds Cations are always smaller than the parent atom Structures of Ionic Compounds Anions are always larger than the parent atom

Section 12.2 Characteristics of Ions and Ionic Compounds B. Ionic bonding and Structures of Ionic Compounds Polyatomic ions work in the same way as simple ions –The covalent bonds hold the polyatomic ion together so it behaves as a unit Ionic Compounds Containing Polyatomic Ions

Section 12.3 Lewis Structures 1.To learn to write Lewis structures 2.To learn to write Lewis structures for molecules with multiple bonds Objectives

Section 12.3 Lewis Structures A. Writing Lewis Structures In writing Lewis structures we include only the valence electrons Most important requirement –Atoms achieve noble gas electron configuration (octet rule, duet rule)

Section 12.3 Lewis Structures A. Writing Lewis Structures Bonding pairs are shared between 2 atoms Unshared pairs (lone pairs) are not shared and not involved in bonding

Section 12.3 Lewis Structures A. Writing Lewis Structures

Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds Single bond – covalent bond in which 1 pair of electrons is shared by 2 atoms Double bond – covalent bond in which 2 pairs of electrons are shared by 2 atoms Triple bond – covalent bond in which 3 pairs of electrons are shared by 2 atoms

Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds –A molecule shows resonance when more than one Lewis structure can be drawn for the molecule

Section 12.3 Lewis Structures B. Lewis Structures of Molecules with Multiple Bonds –Boron – incomplete octet Some Exceptions to the Octet Rule –Molecules containing odd numbers of electrons – NO and NO 2

Section 12.4 Structure of Molecules 1.To understand molecular structure and bond angles 2.To learn to predict molecular geometry from the number of electron pairs 3.To learn to apply the VSEPR model to molecules with double bonds Objectives

Section 12.4 Structure of Molecules A. Molecular Structure Three dimensional arrangement of the atoms in a molecule –Water - bent

Section 12.4 Structure of Molecules A. Molecular Structure Linear structure – atoms in a line –Carbon dioxide

Section 12.4 Structure of Molecules A. Molecular Structure Trigonal planar – atoms in a triangle –BF 3

Section 12.4 Structure of Molecules A. Molecular Structure Tetrahedral structure –methane

Section 12.4 Structure of Molecules B. The VSEPR Model Valence shell electron pair repulsion (VSEPR) model –Molecular structure is determined by minimizing repulsions between electron pairs

Section 12.4 Structure of Molecules B. The VSEPR Model –180 o - linear Two Pairs of Electrons BeCl 2

Section 12.4 Structure of Molecules B. The VSEPR Model –120 o – trigonal planar Three Pairs of Electrons BF 3

Section 12.4 Structure of Molecules B. The VSEPR Model –120 o – tetrahedral Four Pairs of Electrons CH 4

Section 12.4 Structure of Molecules B. The VSEPR Model

Section 12.4 Structure of Molecules B. The VSEPR Model

Section 12.4 Structure of Molecules C. Molecules with Double Bonds When using VSEPR model to predict molecular geometry of a molecule a double bond is counted the same as a single electron pair