Chapter 8 Covalent Bonding and Molecular Structure Chapter 8 Covalent Molecular Structure Bonding and Chapter In Context In this chapter and the next we examine chemical bonding in detail We examined ionic bonding briefly in Chapter 2 and will do so in more detail in Chapter 11 We will also examine intermolecular forces in detail in Chapter 11 Here we will apply what you have learned about atomic structure Chapter 6 electron configurations and periodic trends Chapter 7 to the chemical bonds formed between atoms and ions and the shapes of molecules and ions that contain covalent bonds 8 1 Biology Molecular shape of enzymes specifically allow only certain reactions to occur Drugs are developed that specifically fit into active sites in the enzyme to affect or even stop its action Chapter 8 8 1 Interactions Between Particles Coulomb s Law 8 2 Covalent Bonding Basics 8 3 Lewis Structures 8 4 Bond Properties 8 5 Electron Distribution in Molecules 8 6 Valence Shell Electron Pair Repulsion Theory and Molecular Shape 8 7 Molecular Polarity Chapter Goals Apply Coulomb s Law Understand forces involved in covalent bonding Write Lewis symbols and Lewis structures Predict bond properties Understand charge distribution in molecules Use VSEPR theory Identify polar and nopolar species Chapter 8 Covalent Bonding and Molecular Structure 8 2 8 1 Interactions Between Particles Coulomb s Law OWL Opening Exploration 8 1 Coulomb s Law Matter is made up of atoms and ions that experience both attractive and repulsive forces The strength of the force holding oppositely charged particles together in any material is described by Coulomb s Law equation 8 1 According to this law force of attraction or repulsion between two charged species is directly proportional to the magnitude of the charge on the particles qA and qB in equation 8 1 and inversely proportional to the square of the distance between the two particles r in equation 8 1 q q 8 1 Force A 2 B r For electrons q e and for nuclei q Ze where Chapter Goals Revisited Apply Coulomb s Law Understand relationship between charge distance and force of attraction or repulsion e magnitude of electron charge 1 6022 x 10 19 C Z nuclear charge number of protons r distance between particles A and B All chemical attractive forces involve opposite charges such as those between protons in a nucleus and the electrons surrounding that nucleus and between positive and negative ions The type and strength of these attractive forces allow us to categorize the different types of bonding found in matter Table 8 1 In ionic bonding found in ionic solids and liquids such as NaCl and CaCO3 there are strong attractive forces between positively and negatively charged ions Covalent bonding the attractive forces between electrons and nuclei on adjacent atoms within a molecule occurs in compounds such as H2O and NH3 Another type of attraction takes place in pure metals Metallic bonding the attractive forces between electrons and nuclei in metals occurs in metals such as Cu and Fe and will be discussed in more detail in Chapter 9 Finally there are forces that exist between molecules called intermolecular forces which will be discussed in more detail in Chapter XX Table 8 1 Types of Chemical Bonding Type of Interaction Source of Attractive Forces Ionic Bonding Oppositely charged ions Covalent Bonding Nuclei and valence electrons Metallic Bonding Nuclei and electrons Intermolecular Forces Partial charges on individual separate molecules 8 2 Covalent Bonding Basics OWL Opening Exploration 8 2 A covalent bond is characterized by the sharing of valence electrons by two adjacent atoms This happens most often between nonmetal elements such as carbon hydrogen oxygen and nitrogen For example consider a simple covalently bonded molecule H2 When two isolated H atoms are at a great distance from one another they feel no attractive or repulsive forces However as the atoms approach more closely the attractive and repulsive forces between the two atoms become important Chapter Goals Revisited Understand forces involved in covalent bonding Identify attractive and repulsive forces between atoms Chapter 8 Covalent Bonding and Molecular Structure 8 3 H represents valence electron represents nucleus There are two types of repulsive forces between the two atoms First the nuclei repel because they are both positively charged Second the electrons repel because they are both negatively charged The attractive forces between the two atoms result from the interaction between the positively charged nucleus on one hydrogen atom and the negatively charged electron on the other hydrogen atom In summary for two hydrogen atoms HA and HB Repulsive Forces Attractive Forces electron A electron B nucleus A nucleus B electron A nucleus B electron B nucleus A In general when two atoms approach each other these repulsive and attractive forces always occur When the attractive forces are greater than the repulsive forces a covalent bond forms When the repulsive forces are greater than the attractive forces a covalent bond does not form and the atoms remain isolated The balance between the attractive and repulsive forces in H2 is related to the distance between H atoms as shown in Figure 8 1 At large distances neither attractive nor repulsive forces are important and no bond forms between H atoms At short distances repulsive forces are stronger than attractive forces and no bond forms Figure 8 1 Energy of H2 as a function of internuclear distance At an internuclear distance where the attractive forces are stronger than the repulsive forces a bond forms between the H atoms The two valence electrons pair up and are shared between the two hydrogen nuclei in a covalent bond that is represented by a single line connecting the H atoms H H H H The single line between H atoms in H2 is a very useful representation of a chemical bond but it is does not give an accurate picture of the distribution of bonding electrons in the Flashforward 9 6 Molecular Orbital Theory Chapter 8 Covalent Bonding and Molecular Structure 8 4 H2 molecule More sophisticated descriptions of chemical bonding will be discussed in Chapter 9 8 3 Lewis Structures OWL Opening Exploration 8 X One of the most important tools chemists use to predict the properties of a chemical species is its Lewis structure A Lewis structure also called a Lewis dot structure or Lewis diagram shows the arrangement of valence electrons both bonding and nonbonding and nuclei in