Chapter 8 Covalent Bonding and Molecular Structure

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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,Chapter Goals Revisited,Apply Coulomb s Law. Understand, Matter is made up of atoms and ions that experience both attractive and repulsive forces relationship between. The strength of the force holding oppositely charged particles together in any material is charge distance and. described by Coulomb s Law equation 8 1 According to this law force of attraction force of attraction or. or repulsion between two charged species is directly proportional to the magnitude of the repulsion. 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. Force A 2 B 8 1,For electrons q e and for nuclei q Ze. where 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. Chapter Goals Revisited,Understand forces,involved in covalent.
A covalent bond is characterized by the sharing of valence electrons by two adjacent Identify attractive and. atoms This happens most often between nonmetal elements such as carbon hydrogen repulsive forces. oxygen and nitrogen between atoms, 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 8 Covalent Bonding and Molecular Structure 8 3. represents valence electron,H 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 electron A electron B. nucleus A nucleus B,Attractive Forces 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,Flashforward, The single line between H atoms in H2 is a very useful representation of a chemical bond 9 6 Molecular Orbital Theory. but it is does not give an accurate picture of the distribution of bonding electrons in the. Chapter 8 Covalent Bonding and Molecular Structure 8 4. H2 molecule More sophisticated descriptions of chemical bonding will be discussed in. 8 3 Lewis Structures,OWL Opening Exploration,Chapter Goals Revisited. Write Lewis symbols and, One of the most important tools chemists use to predict the properties of a chemical Lewis structures.
species is its Lewis structure A Lewis structure also called a Lewis dot structure or Use the periodic table. Lewis diagram shows the arrangement of valence electrons both bonding and and valence electrons. nonbonding and nuclei in covalently bonded molecules and ions The simplest Lewis to write Lewis. structure is the Lewis symbol for an element where the element symbol represents the symbols. nucleus and core non valence electrons and dots represent valence electrons As. shown in the Lewis symbols in Figure 8 2 valence electrons are traditionally arranged. around the four sides of the element symbol The electrons are single or paired to reflect. the electron configuration of the element and the Pauli exclusion principle. Figure 8 2 Lewis symbols for the 2 period elements. nd Flashback, The Lewis symbols for the elements in the 2 period Figure 8 2 show the relationship. between valence electrons and group number for the A group main group elements 7 3 Electron Configuration. Recall that the number of valence electrons for any main group element is equal to the of Elements. group number for that element,EXAMPLE PROBLEM Lewis Symbols for Atoms. a Draw the Lewis symbol for Te tellurium, b The following Lewis diagram represents the valence electron configuration of a main group element. Identify the element in period 5 that has this valence electron configuration. a Tellurium is a Group 6A element and has six valence electrons. b Rb The element has one valence electron so it is a Group 1A element Rubidium is the Group 1A element in the fifth. OWL Example Problems,8 3 Lewis Symbols for Atoms, The representation of H2 shown in the previous section where the bonding electron are. represented with a line H H is the Lewis structure of H2 In a Lewis structure pairs of. bonding electrons are represented as lines connecting atom symbols and nonbonding. electrons are shown as dots Figure 8 3 Nuclei and core electrons are represented by. element symbols Notice in Figure 8 3 that there can be more than one bonding pair. between atoms and that nonbonding electrons usually appear in pairs called lone. electron pairs or lone pairs A bond consisting of two electrons one line is called a. single bond a bond made up of 4 electrons two pairs two lines is called a double. bond and a bond with 6 electrons three pairs three lines is called a triple bond. Chapter 8 Covalent Bonding and Molecular Structure 8 5. Figure 8 3 Lewis structures for C2H4 and ICl, Lewis structures are very useful in visualizing the physical and chemical properties of Lewis Dot.
compounds made up of nonmetal elements We will begin by learning how to create Number Structure. Lewis dot structures and then in the following sections use Lewis structures to explore. Electron Pair, bond properties bond order bond length bond energy bond polarity the shapes of Bond Order Geometry. molecules molecular polarity and how the shape and polarity of molecules influence. chemical properties Resonance,Structures Shape,Reactivity. Drawing Lewis Structures Electron Molecular Physical Properties. Distribution Polarity Vapor Pressure, The most important guideline to follow when drawing Lewis structures is the octet rule Solubility. Boiling and Melting Points, The octet rule states that most atoms in a Lewis structures are surrounded by no more. than 8 electrons shared bonding electrons and unshared nonbonding electrons The. octet rule is related to the fact that valence shells contain a single s orbital and three p. orbitals that can accommodate up to 8 electrons and it is these orbitals that are most. often involved in forming covalent bonds between nonmetals in covalent compounds. There are however some exceptions to the octet rule. Hydrogen has a single valence electron in a 1s orbital and therefore only Chapter Goals Revisited. accommodates two electrons when it forms covalent bonds It typically forms Write Lewis symbols and. Lewis structures, only one chemical bond to another atom and does not have lone pairs in Lewis Use octet rule to write.
structures Lewis symbols, Beryllium and boron often accommodate only 4 or 6 electrons respectively in. Lewis structures, Elements with available empty d orbitals in the valence shell elements in the. third period and below can accommodate more than eight electrons often 10 or. When determining if elements have satisfied octets assign lone pairs of electrons to the. element they are placed around and divide bonding electrons equally between the two. atoms that are connected by the bond, In addition to the octet rule it is helpful to remember that only the elements C N O P. and S typically form double and triple bonds with other elements Lewis structures are. drawn by following the five steps shown in the examples below. Chapter 8 Covalent Bonding and Molecular Structure 8 6. Example PF3 Example CO2, Step 1 Count Valence Electrons Phosphorus has 5 valence Carbon has 4 valence electrons and. Count the total number of valence electrons electrons and each fluorine has 7 each oxygen has 6 valence electrons. in the molecule or ion Anions have extra valence electrons 4 2 6 16 electrons. electrons so add 1 electron for each 5 3 7 26 electrons or 8 electron pairs. negative charge Cations have a deficiency or 13 electron pairs. of electrons so subtract 1 electron for each,positive charge.
Step 2 Arrange Atoms, The central atom is usually the one with the F P F. lowest affinity for electrons the one farthest O C O. from fluorine on the periodic table F,Exception H is never a central atom. Step 3 Add Single Bonds F P F,Add one bond using a line between each O C O. terminal atom and the central atom Each F, bond represents 2 electrons 16 electrons 4 bonding electrons. 26 electrons 6 bonding electrons 12 electrons remaining. 20 electrons remaining,Step 4 Add Remaining Electrons F P F.
Assign any remaining electrons to the O C O,terminal atoms in pairs until the octet rule F. is satisfied for each terminal atom except Each O needs 3 pairs to satisfy the. hydrogen If additional electrons remain Each F needs 3 pairs to satisfy the. octet rule No other electrons remain, add them to the central atom octet rule and the one remaining. to satisfy the octet rule for C,pair is assigned to P. Step 5 Octet Rule Check,Use the octet rule to determine if multiple. bonds are necessary between atoms If,there is an electron deficiency for an F P F.
element change a non bonding electron,pair lone pair on an adjacent atom into a F. bonding pair Continue only until the octet The central atom is sharing only 4. All elements have complete octets, rule is satisfied for all elements other than electrons Use one lone pair on each. the known exceptions oxygen to make a second bond to. carbon satisfying the octet rule, The steps above can also be applied to the Lewis structures of ions When drawing the. Lewis structure for an ionic species the structure is placed within square brackets and the. ion charge is shown outside the brackets For example the steps required to draw the. Lewis structure for SO32 are shown below, Step 1 Sulfur has 6 valence electrons each oxygen has 6 valence electrons and. the 2 charge on the ion adds two more electrons,6 3 6 2 26 valence electrons or 13 pairs.
Steps 2 and 3 O S O Steps 4 and 5,OWL Example Problems. 8 5 Drawing Lewis Structures Tutor, Chapter 8 Covalent Bonding and Molecular Structure 8 7. Exceptions to the Octet Rule, Beryllium and boron are often found with fewer than 8 electrons in electron deficient. compounds compounds in which an element has an incomplete octet For example BF3. is an electron deficient compound, Each fluorine has a complete octet 6 nonbonding electrons 2 bonding electrons but. boron has only 6 electrons 6 bonding electrons and no lone pairs Changing a fluorine. lone pair to a bonding pair would alleviate the electron deficiency but neither element. commonly forms multiple bonds The electron deficiency affects the reactivity of BF3. Consider the reaction between BF3 and NH3, In this reaction the lone pair on N is used to form a bond to B Following the reaction.
both N and B have full octets and the compound is not electron deficient Chapter Goals Revisited. A second exception to the octet rule that also involves elements with incomplete octets Write Lewis symbols and. Chapter 8 Covalent Bonding and Molecular Structure 8 5 Figure 8 3 Lewis structures for C 2H 4 and ICl Lewis structures are very useful in visualizing the physical and chemical properties of compounds made up of nonmetal elements We will begin by learning how to create Lewis dot structures and then in the following sections use Lewis structures to explore bond properties bond order bond

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