General, Organic, and Biological Chemistry. Fourth Edition Karen Timberlake. Chapter 5. Compounds and Their Bonds Pearson Education, Inc.

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds 2013 Pearson Education, Inc.

Electrons and Reactivity Atoms contain a very small nucleus packed with neutrons and positively charged protons. a large volume of space around the nucleus that contains the negatively charged electrons. It is the electrons that determine the physical and chemical properties of atoms. Elements react in order to achieve the same electronic structure of the nearest noble gas 2013 Pearson Education, Inc. Chapter 3, Section 3 2

Electrons and Reactivity Atoms contain a very small nucleus packed with neutrons and positively charged protons. a large volume of space around the nucleus that contains the negatively charged electrons. It is the electrons that determine the physical and chemical properties of atoms. Elements react in order to achieve the same electronic structure of the nearest noble gas 2013 Pearson Education, Inc. Chapter 3, Section 3 3

Ionic and Covalent Bonds Atoms form octets to become more stable. by losing, gaining, or sharing valence electrons. by forming ionic or covalent bonds. 2013 Pearson Education, Inc. Chapter 5, Section 1 4

Covalent Compounds Covalent compounds are formed when nonmetals share valence electrons forming a covalent bond. Covalent compounds consist of molecules, which are discrete groups of atoms, such as: water, H 2 O 2 H atoms + 1 O atom carbon dioxide, CO 2 1 C atom + 2 O atoms glucose, C 6 H 12 O 6 6 C atoms + 12 H atoms + 6 O atoms 2013 Pearson Education, Inc. Chapter 5, Section 1 5

Ionic Compounds Ionic compounds are formed when metal atoms transfer electrons to nonmetal atoms resulting in the formation of ionic bonds. Ionic compounds we use every day include: table salt NaCl baking soda NaHCO 3 milk of magnesia Mg(OH) 2 2013 Pearson Education, Inc. Chapter 5, Section 1 6

Ionic Compounds, Minerals Precious and semiprecious gemstones are also examples of ionic compounds called minerals. Sapphires and rubies are made of aluminum oxide (Al 2 O 3 ), which is an ionic compound. Their brilliant colors come from the presence of other metals such as chromium, which make rubies red and iron and titanium, which make sapphires blue 2013 Pearson Education, Inc. Chapter 5, Section 1 7

Octet Rule The octet rule is the tendency for atoms to share or transfer electrons to obtain a stable configuration of 8 valence electrons. 2013 Pearson Education, Inc. Chapter 5, Section 1 8

Octet Rule The octet rule is associated with the stability of the noble gases except for He, which is stable with 2 valence electrons (duet). Valence Electrons He 1s 2 2 Ne 1s 2 2s 2 2p 6 8 Ar 1s 2 2s 2 2p 6 3s 2 3p 6 8 Kr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 8 2013 Pearson Education, Inc. Chapter 5, Section 1 9

Metals Form Positive Ions Metals form positive ions called cations by a loss of their valence electrons. with the electron configuration of the nearest noble gas. that have fewer electrons than protons. Group 1A (1) metals ion 1+ Group 2A (2) metals ion 2+ Group 3A (3) metals ion 3+ 2013 Pearson Education, Inc. Chapter 5, Section 1 10

Formation of a Sodium Ion, Na + Sodium achieves an octet by losing its one valence electron. 2013 Pearson Education, Inc. Chapter 5, Section 1 11

Charge of Sodium Ion, Na + With the loss of its valence electron, a sodium ion has a 1 + charge. ion Na atom Na + charge 2013 Pearson Education, Inc. Chapter 5, Section 1 12

Formation of Magnesium Ion, Mg 2+ Magnesium achieves an octet by losing its two valence electrons. 2013 Pearson Education, Inc. Chapter 5, Section 1 13

Charge of Magnesium Ion, Mg 2+ With the loss of two valence electrons magnesium forms a positive ion with a 2 + charge. Mg atom Mg 2+ ion charge 2013 Pearson Education, Inc. Chapter 5, Section 1 14

Formation of Negative Ions In ionic compounds, nonmetals achieve an octet arrangement. gain electrons. form negatively charged ions called anions with 3, 2, or 1 charges. 2013 Pearson Education, Inc. Chapter 5, Section 1 15

Formation of a Chloride Ion, Cl Chlorine achieves an octet by adding one more electron to its 7 valence electrons. 2013 Pearson Education, Inc. Chapter 5, Section 1 16

Charge of a Chloride Ion, Cl By gaining one electron, the chloride ion has a 1 charge. charge 2013 Pearson Education, Inc. Chapter 5, Section 1 17

Ionic Charge from Group Numbers Ions achieve the electron configuration of their nearest noble gas by forming positive ions with a charge equal to its Group number. Group 1A (1) = 1 + Group 2A (2) = 2 + Group 3A (3) = 3 + negative ions with a charge obtained by subtracting 8 or 18 from its Group number. 2013 Pearson Education, Inc. Chapter 5, Section 1 18

Some Typical Ionic Charges 2013 Pearson Education, Inc. Chapter 5, Section 1 19

Group Numbers for Some Positive and Negative Ions 2013 Pearson Education, Inc. Chapter 5, Section 1 20

Chapter 5 Compounds and Their Bonds 5.2 Writing names and formulas for ionic compounds 2013 Pearson Education, Inc. 2013 Pearson Education, Inc. Chapter 5, Section 1 21

Ionic Compounds Ionic compounds consist of positive and negative ions. have attractive forces between the positive and negative ions called ionic bonds. have high melting and boiling points. are solid at room temperature. 2013 Pearson Education, Inc. Chapter 5, Section 1 22

Salt Is an Ionic Compound Sodium chloride, or table salt, is an example of an ionic compound. 2013 Pearson Education, Inc. Chapter 5, Section 1 23

Formulas of Ionic Compounds The chemical formula of an ionic compound represents the element symbols and subscripts, which represent the lowest whole-number ratio of ions. In the formula of an ionic compound, the sum of positively and negatively charged ions is always zero Rule of Zero Charge the charges are balanced. 2013 Pearson Education, Inc. Chapter 5, Section 1 24

Charge Balance for NaCl, Salt In NaCl, a Na atom loses its valence electron. a Cl atom gains an electron. the symbol of the metal (sodium) is written first, followed by the symbol of the nonmetal (chlorine). 2013 Pearson Education, Inc. Chapter 5, Section 1 25

Charge Balance In MgCl 2 In MgCl 2, a Mg atom loses two valence electrons. two Cl atoms gain one electron each. subscripts indicate the number of ions needed to give charge balance. the symbol of the metal (magnesium) is written first, followed by the symbol of the nonmetal (chlorine). 2013 Pearson Education, Inc. Chapter 5, Section 1 26

Writing Formulas For Binary Ionic Compounds Binary ionic compounds are made from 2 elements, a metal and a nonmetal. Charge balance is used to write the formula for sodium nitride, a compound containing Na + and N 3. The metal ion is written first, followed by nonmetal, subscripts indicate how many of each 2013 Pearson Education, Inc. Chapter 5, Section 1 27

Charge Balance in Na 2 S In sodium sulfide, Na 2 S, two Na atoms lose one valence electron each. one S atom gains two electrons. subscripts show the number of ions needed to give charge balance. The group of ions with the lowest ratio of ions in an ionic compound is called a formula unit. 2013 Pearson Education, Inc. Chapter 5, Section 1 28

Formula from Ionic Charges Write the ionic formula of the compound containing Ba 2+ and Cl. Write the symbols of each ion. Ba 2+ Cl Balance the charges. Ba 2+ Cl (two Cl needed) Cl Write the metal first, followed by the nonmetal,, using a subscript to represent the number of. Cl ions. BaCl 2 2013 Pearson Education, Inc. Chapter 5, Section 1 29

Writing Names For Binary Ionic Compounds The name of an Binary ionic compound is made up of 2 elements. has the name of the metal ion written first. has the name of the nonmetal ion written second using the first syllable of its element name. followed by ide. has a space separating the name of the metal and nonmetal. 2013 Pearson Education, Inc. Chapter 5, Section 1 30

Charges of Representative Elements 2013 Pearson Education, Inc. Chapter 5, Section 3 31

Naming Binary Ionic Compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 32

Naming Mg 3 N 2 Step 1 Identify the cation and anion. The cation from Group 2A (2) is Mg 2+, and the anion from Group 5A (15) is N 3. Step 2 Name the cation by its element name. Cation: Mg 2+ is magnesium Step 3 Name the anion by using the first syllable of its element name followed by ide. Anion: nitrogen becomes nitride, N 3 Step 4 Write the name for the cation first and the name for the anion second. Mg 3 N 2 is magnesium nitride. 2013 Pearson Education, Inc. Chapter 5, Section 1 33

What do you notice about these names and formulas? Chemical Formula Fe 2 O 3 FeCl 2 PbS AlP CuF 2 SnI 4 KBr Written Form iron(iii) oxide iron(ii) chloride lead(ii) sulfide aluminum phosphide copper(ii) fluoride tin(iv) iodide potassium bromide 2013 Pearson Education, Inc. Chapter 5, Section 1 34 34

Metals with Variable Ion Charge Most transition metals (3-12) and Group 4A (14) metals form 2 or more positive ions, except Zn 2+, Ag +, and Cd 2+, which form only one ion. 2013 Pearson Education, Inc. Chapter 5, Section 1 35

Metals with Variable Charge The names of transition metals with two or more positive ions (cations) use a Roman numeral after the name of the metal to identify the ion charge. 2013 Pearson Education, Inc. Chapter 5, Section 1 36

Naming Ionic Compounds with Variable Charge Metals 2013 Pearson Education, Inc. Chapter 5, Section 1 37

Naming FeCl 2 Step 1 Determine the charge of the cation from the anion. Analyze the Problem. 2013 Pearson Education, Inc. Chapter 5, Section 1 38

Naming FeCl 2 Step 2 Name the cation by its element name and use a Roman numeral in parentheses for the charge. Fe 2+ = iron(ii) Step 3 Name the anion by using the first syllable of its element name followed by ide. Cl = chloride Step 4 Write the name for the cation first and the name for the anion second. iron(ii) chloride 2013 Pearson Education, Inc. Chapter 5, Section 1 39

Examples of Names of Compounds with Variable Charge Metals 2013 Pearson Education, Inc. Chapter 5, Section 1 40

What do you notice about these names and formulas? Chemical Formula (NH 4 ) 2 S CoSO 4 Fe(OH) 3 Ca 3 (PO 4 ) 2 NH 4 NO 3 Written Form ammonium sulfide cobalt (II) sulfate iron (III) hydroxide calcium phosphate ammonium nitrate 2013 Pearson Education, Inc. Chapter 5, Section 1 41 41

Polyatomic Ions A polyatomic ion is a group of atoms. has an overall ionic charge. Examples: NH + 4 ammonium OH hydroxide NO 3 nitrate NO 2 nitrite CO 2 3 carbonate PO 3 4 phosphate HCO 3 hydrogen carbonate (bicarbonate) 2013 Pearson Education, Inc. Chapter 5, Section 1 42

Some Names of Polyatomic Ions The names of common polyatomic anions end in ate. NO 3 nitrate PO 3 4 phosphate with one oxygen less, end in ite NO 2 nitrite PO 3 3 phosphite with hydrogen attached, use prefix hydrogen (or bi). HCO 3 hydrogen carbonate (bicarbonate) HSO 3 hydrogen sulfite (bisulfite) 2013 Pearson Education, Inc. Chapter 5, Section 1 43

Compounds Containing Polyatomic Ions Polyatomic ions must be associated with an ion of opposite charge. form ionic bonds with ions of opposite charge to achieve charge balance. Example: charge balance: Ca 2+ calcium NO 3 nitrate ion Ca(NO 3 ) 2 calcium nitrate 2013 Pearson Education, Inc. Chapter 5, Section 1 44

Some Compounds with Polyatomic Ions 2013 Pearson Education, Inc. Chapter 5, Section 1 45

Guide to Naming Compounds with Polyatomic Ions 2013 Pearson Education, Inc. Chapter 5, Section 1 46

Name K 2 SO 4 Step 1 Identify the cation and polyatomic ion (anion). Cation: K + Anion: SO 2 4 Step 2 Name the cation, using a Roman numeral if needed. K + = potassium ion Step 3 Name the polyatomic ion. SO 2 4 = sulfate ion Step 4 Write the name or the compound, cation first and the polyatomic ion second. K 2 SO 4 = potassium sulfate 2013 Pearson Education, Inc. Chapter 5, Section 1 47

Guide to Writing Formulas for Compounds with Polyatomic Ions 2013 Pearson Education, Inc. Chapter 5, Section 1 48

Write the Formula for Aluminium Hydroxide Step 1 Identify the cation and polyatomic ion (anion). Al 3+ and OH Step 2 Balance the charges. 2013 Pearson Education, Inc. Chapter 5, Section 1 49

Write the Formula for Aluminium Hydroxide Step 3 Write the formula, cation first, using the subscripts from charge balance. Al(OH) 3 2013 Pearson Education, Inc. Chapter 5, Section 1 50

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds 5.5 Covalent Compounds: Sharing Electrons 2013 Pearson Education, Inc. Lectures 2013 Pearson Education, Inc. Chapter 5, Section 1 51

Covalent Bonds Covalent bonds form when atoms of nonmetals share electrons to complete octets. Valence electrons are not transferred, but shared to achieve stability. 2013 Pearson Education, Inc. Chapter 5, Section 1 52

Formation of H 2 In the simplest covalent molecule, H 2, the H atoms increase attraction as they move closer. share electrons to achieve a stable configuration. form a covalent bond. 2013 Pearson Education, Inc. Chapter 5, Section 1 53

Formation of H 2 2013 Pearson Education, Inc. Chapter 5, Section 1 54

Electron-Dot Formulas of Covalent Molecules In a fluorine (F 2 ) molecule, the F atoms share one of their valence electrons. acquire an octet. form a covalent bond. 2013 Pearson Education, Inc. Chapter 5, Section 1 55

Elements That Exist as Diatomic Molecules These seven elements share electrons to form diatomic, covalent molecules. BrINClHOF! Remember it! 2013 Pearson Education, Inc. Chapter 5, Section 1 56

Bonding Patterns of Some Nonmetals The number of covalent bonds a nonmetal forms is usually equal to the number of electrons it needs to acquire a stable electron configuration. Typical bonding patterns for some nonmetals are shown in the table below. 2013 Pearson Education, Inc. Chapter 5, Section 1 57

Bonding Patterns of Some Nonmetals Biological molecules tend to be made out of H, O,N, and C mostly. Bonding tendency rule for H, O, N, C HONC 1234 Rule Hydrogen tends to form 1 bond Oxygen tends to form 2 bonds Nitrogen tends to form 3 bonds Carbon tends to form 4 bonds 2013 Pearson Education, Inc. Chapter 5, Section 1 58

Electron-Dot Formulas for Some Covalent Compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 59

Guide to Drawing Electron-Dot Formulas 2013 Pearson Education, Inc. Chapter 5, Section 1 60

Draw the Electron-Dot Formula for NH 3 Step 1 Determine the arrangement of atoms. In NH 3, N is the central atom and is bonded to three H atoms. Step 2 Determine the total number of valence electrons. Total valence electrons for NH 3 = 8 e 2013 Pearson Education, Inc. Chapter 5, Section 1 61

Draw the Electron-Dot Formula for NH 3 Step 3 Attach each bonded atom to the central atom with a pair of electrons. 2013 Pearson Education, Inc. Chapter 5, Section 1 62

Draw the Electron-Dot Formula for NH 3 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. 8 valence e 6 bonding e = 2 e remaining Use the remaining 2 e to complete the octet around the N atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 63

Exceptions to the Octet Rule Not all atoms have octets. Some can have less than an octet, such as H, which requires only 2 electrons, B, which requires only 3 electrons, and Be, which requires only 4 electrons. Some can have expanded octets, such as P, which can have 10 electrons, S, which can have 12 electrons, and Cl, Br and I, which can have 14 electrons 2013 Pearson Education, Inc. Chapter 5, Section 1 64

Single and Multiple Bonds In many covalent compounds, atoms share two or three pairs of electrons to complete their octets. In a single bond, one pair of electrons is shared. In a double bond, two pairs of electrons are shared. In a triple bond, three pairs of electrons are shared. 2013 Pearson Education, Inc. Chapter 5, Section 1 65

Draw the Electron-Dot Formula for CS 2 Step 1 Determine the arrangement of atoms. In CS 2, C is the central atom and is bonded to two S atoms. 2013 Pearson Education, Inc. Chapter 5, Section 1 66

Draw the Electron-Dot Formula for CS 2 Step 2 Determine the total number of valence electrons. Total valence electrons for 2013 Pearson Education, Inc. Chapter 5, Section 1 67

Draw the Electron-Dot Formula for CS 2 Step 3 Attach each bonded atom to the central atom with a pair of electrons. A pair of bonding electrons (single bond) is placed between each S atom and the central C atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 68

Draw the Electron-Dot Formula for CS 2 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. 16 valence e - 4 bonding e = 12 e remaining The remaining 12 electrons are placed as six lone pairs of electrons on both S atoms. However, this does not complete the octet for the C atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 69

Draw the Electron-Dot Formula for CS 2 Step 4 Continued: Double and Triple Covalent Bonds: To complete the octet for the C atom, it needs to share an additional lone pair from each of the S atoms, forming a double bond with each S atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 70

A Nitrogen Molecule has a Triple Bond In a nitrogen molecule, N 2, each N atom shares 3 electrons, each N atom attains an octet, and the sharing of 3 sets of electrons is called a triple bond. 2013 Pearson Education, Inc. Chapter 5, Section 1 71

Resonance Structures Resonance structures are two or more electron-dot formulas for the same arrangement of atoms. related by a double-headed arrow ( ). written by changing the location of a double bond between the central atom and a different attached atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 72

Writing Resonance Structures for SO 2 Sulfur dioxide has two resonance structures. Step 1 Determine the arrangement of atoms. In SO 2, the S atom is the central atom. O S O Step 2 Determine the total number of valence electrons. Total valence electrons for 2013 Pearson Education, Inc. Chapter 5, Section 1 73

Writing Resonance Structures for SO 2 Step 3 Attach each bonded atom to the central atom with a pair of electrons. 2013 Pearson Education, Inc. Chapter 5, Section 1 74

Writing Resonance Structures for SO 2 Step 4 Place the remaining electrons using single or multiple bonds to complete the octets. The remaining 14 electrons are drawn as lone pairs of electrons to complete the octets of the O atoms, but not the S atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 75

Writing Resonance Structures for SO 2 Step 4 Continued: To complete the octet for S, an additional lone pair from one of the O atoms is shared to form a double bond. Because the shared lone pair of electrons can come from either O atom, two resonance structures can be drawn. 2013 Pearson Education, Inc. Chapter 5, Section 1 76

Learning Check FNO 2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure? 2013 Pearson Education, Inc. Chapter 5, Section 1 77

Solution FNO 2, a rocket propellant, has two resonance structures. One is shown below. What is the other resonance structure? 2013 Pearson Education, Inc. Chapter 5, Section 1 78

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds 5.6 Naming and Writing Covalent Formulas 2013 Pearson Education, Inc. Lectures 2013 Pearson Education, Inc. Chapter 5, Section 1 79

Names of Covalent Compounds When naming a covalent compound, the first nonmetal in the formula is named by its element name, and the second nonmetal is named using the first syllable of its element name, followed by ide. Prefixes are used to indicate the number of atoms present for each element in the compound, and because two nonmetals can form two or more different compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 80

Prefixes Used in Naming Covalent Compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 81

Some Covalent Compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 82

Guide to Naming Covalent Compounds with Two Nonmetals 2013 Pearson Education, Inc. Chapter 5, Section 1 83

Naming Covalent Compounds, SO 2 Analyze the Problem. Symbols of Elements S Name sulfur oxygen Subscripts 1 2 Prefix (none) understood di Step 1 Name the first nonmetal by its element name. In SO 2, the first nonmetal (S) is sulfur. O 2013 Pearson Education, Inc. Chapter 5, Section 1 84

Naming Covalent Compounds, SO 2 Step 2 Name the second nonmetal by using the first syllable of its name followed by ide. The second nonmetal (O) is named oxide. Step 3 Add prefixes to indicate the number of atoms (subscripts). Because there is one sulfur atom, no prefix is needed. The subscript two for the oxygen atoms is written as the prefix di. The name of SO 2 is sulfur dioxide. 2013 Pearson Education, Inc. Chapter 5, Section 1 85

Learning Check Name the covalent compound P 2 O 5. 2013 Pearson Education, Inc. Chapter 5, Section 1 86

Solution Name the covalent compound P 2 O 5. Analyze the Problem. Symbols of Elements P O Name phosphorus oxygen Subscripts 2 5 Prefix di penta Step 1 Name the first nonmetal by its element name. In P 2 O 5, the first nonmetal (P) is phosphorus. 2013 Pearson Education, Inc. Chapter 5, Section 1 87

Solution Step 2 Name the second nonmetal by using the first syllable of its name followed by ide. The second nonmetal (O) is named oxide. Step 3 Add prefixes to indicate the number of atoms (subscripts). The subscript for the two P atoms is di; the subscript for the five oxygen atoms is penta. The name of P 2 O 5 is phosphorus pentoxide. When the vowels o and o, or a and o appear together (pentaoxide), the first vowel is omitted. 2013 Pearson Education, Inc. Chapter 5, Section 1 88

Guide to Writing Formulas for Covalent Compounds 2013 Pearson Education, Inc. Chapter 5, Section 1 89

Writing Formulas of Covalent Compounds Write the formula for sulfur hexafluoride. Analyze the Problem. Name sulfur hexafluoride Symbols of Elements S F Subscripts 1 6 (from hexa) Step 1 Write the symbols in order of the elements in the name. S F Step 2 Write any prefixes as subscripts. Prefix hexa = 6 Formula: SF 6 2013 Pearson Education, Inc. Chapter 5, Section 1 90

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds The Shape of Molecules 2013 Pearson Education, Inc. Lectures 2013 Pearson Education, Inc. Chapter 5, Section 1 91

Valence-Shell Electron-Pair Repulsion Theory (VSEPR) In the valence-shell electron-pair repulsion (VSEPR) theory, the electron groups around a central atom are arranged as far apart from each other as possible. have the least amount of electron-electron repulsion. are used to predict the molecular shape. 2013 Pearson Education, Inc. Chapter 5, Section 1 92

Molecular Shape why does it matter? Watson and Crick with their famous 3-D model of DNA How did they know? Shape of molecules important as it influences their physical and chemical behavior 2013 Pearson Education, Inc. Chapter 5, Section 1 93

What Determines the 3-D Shape of a Molecule? Need to understand electrostatic repulsion (electron clouds around the central atom in a molecule are going to repel each other) Need to draw Lewis structures Need to differentiate between lone pair electrons and bonding pair electrons around the central atom in a molecule Need to apply a theory based on all of the above 2013 Pearson Education, Inc. Chapter 5, Section 1 94

Lewis Structure Lone pair e- (nonbonding e- domain) Bonding pair e- (bonding domain) Electron pairs are also called domains Electron domains try to stay out of each others way (to minimize repulsion) 2013 Pearson Education, Inc. Chapter 5, Section 1 95

Valence Shell Electron Pair Repulsion Theory VSEPR, for short Proposed by English chemist Ron Gillespie in the 1950s Based on Lewis structures of molecules and electron repulsion 2013 Pearson Education, Inc. Chapter 5, Section 1 96

VSEPR Theory Rules 1. In a molecule, electron domains (pairs) will orient themselves around the central atom in an arrangement that minimizes the repulsions among them. 2. The three dimensional orientation of the outer atoms around the central atom depends on the numbers and types of e- domains 3. Lone pair electrons count as 1 electron domain; single, double or triple bonding pair electrons count as 1 electron domain. 2013 Pearson Education, Inc. Chapter 5, Section 1 97

Shapes of Molecules The three-dimensional shape of a molecule can be predicted by the number of bonding groups (bonding domains) and lone-pair electrons (nonbonding domains) around the central atom in the molecule VSEPR theory (valence-shell-electron-pair repulsion). 2013 Pearson Education, Inc. Chapter 5, Section 1 98

Molecules with Two Electron Domains In a molecule of BeCl 2, there are two electron groups bonded to the central atom, Be (Be is an exception to the octet rule). to minimize repulsion, the arrangement of two electron groups is 180, or opposite each other. the shape of the molecule is linear. 2013 Pearson Education, Inc. Chapter 5, Section 1 99

Molecules With Three Electron Domains In a molecule of BF 3, three electron groups are bonded to the central atom B (B is an exception to the octet rule). repulsion is minimized with 3 electron groups at angles of 120. the shape is trigonal planar. 2013 Pearson Education, Inc. Chapter 5, Section 1 100

Three Electron Domains with a Lone Pair In a molecule of SO 2, S has 3 electron groups; 2 electron groups bonded to O atoms and one lone pair. repulsion is minimized with the electron groups at angles of 120, a trigonal planar arrangement. the shape is determined by the two O atoms bonded to S, giving SO 2 a bent (~120 ) shape. 2013 Pearson Education, Inc. Chapter 5, Section 1 101

Four Electron Domains In a molecule of CH 4, there are four electron groups around C. repulsion is minimized by placing four electron groups at angles of 109, which is a tetrahedral arrangement. the four bonded atoms form a tetrahedral shape. 2013 Pearson Education, Inc. Chapter 5, Section 1 102

Four Electron Groups with a Lone Pair In a molecule of NH 3, three electron groups bond to H atoms, and the fourth one is a lone (nonbonding) pair. repulsion is minimized with 4 electron groups in a tetrahedral arrangement. the three bonded atoms form a pyramidal (~109 ) shape. 2013 Pearson Education, Inc. Chapter 5, Section 1 103

Four Electron Groups with Two Lone Pairs In a molecule of H 2 O, two electron groups are bonded to H atoms and two are lone pairs (4 electron groups). four electron groups minimize repulsion in a tetrahedral arrangement. the shape with two bonded atoms is bent (~109 ). 2013 Pearson Education, Inc. Chapter 5, Section 1 104

Molecular Shapes for 2 and 3 Bonded Atoms 2013 Pearson Education, Inc. Chapter 5, Section 1 105

Molecular Shapes for 4 Bonded Atoms 2013 Pearson Education, Inc. Chapter 5, Section 1 106

Guide to Predicting Molecular Shape (VSEPR Theory) 2013 Pearson Education, Inc. Chapter 5, Section 1 107

Predicting the Molecular Shape of H 2 Se Step 1 Draw the electron-dot formula. In the electron-dot formula for H 2 Se, there are four electron groups, including two lone pairs of electrons around Se. 2013 Pearson Education, Inc. Chapter 5, Section 1 108

Predicting the Molecular Shape of H 2 Se Step 2 Arrange the electron groups around the central atom to minimize repulsion. The four electron groups around Se would have a tetrahedral arrangement. Step 3 Use the atoms bonded to the central atom to determine the molecular shape. Two bonded atoms give H 2 Se a bent shape with a bond angle of ~109. 2013 Pearson Education, Inc. Chapter 5, Section 1 109

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds A closer look at bonding type the concept of electronegativity 2013 Pearson Education, Inc. 2013 Pearson Education, Inc. Chapter 5, Section 1 110

General Rules for Bond Type Negative complex ions Ionic Bond Nonmetal Nonmetal Covalent Bond Metal 2013 Pearson Education, Inc. Chapter 5, Section 1 111

Ionic or Covalent? So far, we have been employing the following generalization for the type of bonding holding atoms together in a substance Generalization metal + nonmetal = ionic bond nonmetal + nonmetal = covalent bond Reality Bonding type is on a continuum, from 100% ionic to 100% covalent! 100% covalent 100% ionic 2013 Pearson Education, Inc. Chapter 5, Section 1 112

Bonding Conundrum Arose in the 1930 s from American Chemist Linus Pauling s work on the nature of the chemical bond. Pauling realized that there was some inbetweeness with the bonding in many substances Calculated the ability of elements to attract electrons to themselves when bonding Called this ability the Electronegativity of the element 2013 Pearson Education, Inc. Chapter 5, Section 1 113 113

Determining Predominant Bond type Electronegativity is a relative measure of the tendency for atoms of an element to attract electrons to themselves in a chemical bond. Originated with American chemist Linus Pauling (1901-1994), a 2x Nobel Prize winner who did most of his work at Cal Poly Tech, but finished his career at Stanford 2013 Pearson Education, Inc. Chapter 5, Section 1 114

2013 Pearson Education, Inc. Chapter 5, Section 1 115

Electronegativity (EN) Values of the Elements Scale ranges from 0.7 to 4.0 2013 Pearson Education, Inc. Chapter 5, Section 1 116

Electronegativity Electronegativity is a measure of an atom s ability to attract electrons to itself in a chemical bond increases from left to right, going across a period on the periodic table. decreases going down a group on the periodic table. is high for the nonmetals, with fluorine as the highest. is low for the metals and transition metals. 2013 Pearson Education, Inc. Chapter 5, Section 1 117

Trends in Periodic table 2013 Pearson Education, Inc. Chapter 5, Section 1 118

Periodic trends in electronegativity Electronegativity decreases down a group because: Atomic radius increases, valence e- further away from nucleus, decreases pulling power of nucleus Electronegativity increases from left to right across a period because: Atomic radius decreases, valence e- closer to the nucleus, increases pulling power of nucleus 2013 Pearson Education, Inc. Chapter 5, Section 1 119

Bonding and Electronegativity According to Pauling, the difference in the electronegativity values of the two atoms involved in a chemical bond can be used to predict the type of bond that forms. Pauling Classified chemical bonds into the following three types, based on differences in electronegativity Ionic Polar Covalent Nonpolar Covalent 2013 Pearson Education, Inc. Chapter 5, Section 1 120

Electronegativity and Bond Type It is the difference in the electronegativies (ΔEN) of two bonded atoms that determines the predominant bond type ΔEN 0.4 Nonpolar covalent bond (e- shared equally between atoms) ΔEN 0.5 to 1.7 polar covalent bond, (e- shared unequally) ΔEN > 1.7 ionic bond (e- transferred) 121 2013 Pearson Education, Inc. Chapter 5, Section 1 121

Bond Character Summary a) Nonpolar covalent bond electrons shared equally b) Polar covalent bond e- not shared equally, more electronegative atom has greater share of e- cloud c) Ionic bond e- transferred from one atom to other, creates a + and ion 2013 Pearson Education, Inc. Chapter 5, Section 1 122

Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. has an equal or almost equal sharing of electrons. has almost no electronegativity difference (0.0 to 0.4). Examples: Atoms Electronegativity Type of Bond Difference 2013 Pearson Education, Inc. Chapter 5, Section 1 123

Example of Nonpolar Covalent Bonds Diatomic elements e.g. H 2 Bonds between P and H = 2.1-2.1=0 2013 Pearson Education, Inc. Chapter 5, Section 1 124

Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms that do not share electrons equally. has a moderate electronegativity difference (0.5 to 1.7). Examples: Atoms Electronegativity Type of Bond Difference 2013 Pearson Education, Inc. Chapter 5, Section 1 125

Comparing Nonpolar and Polar Covalent Bonds 2013 Pearson Education, Inc. Chapter 5, Section 1 126

Result of differences in electronegativity: More electronegative element has greater share of e- cloud, it is electron rich Less electronegative element is e- poor Creation of partial charges on the atoms in the bond (bond dipoles) + and - 2013 Pearson Education, Inc. Chapter 5, Section 1 127

Example: Bond between H and Cl Electronegativity values H= 2.1, Cl = 3.0 e- cloud pulled towards Cl atom = Polar Covalent Bond electron poor region H electron rich region 2.1 3.0 Cl e - rich H Cl + - e - poor Direction e- cloud being pulled 2013 Pearson Education, Inc. Chapter 5, Section 1 128 9.5

Bond Polarity and Dipoles Bonds become more polar as the difference in electronegativity values of bonding atoms increases. Polar covalent bonds have a separation of charges called a dipole. The positive and negative ends of the dipole are indicated by the lowercase Greek letter delta with a positive or negative sign, δ+ and δ-, or an arrow that points from the positive to the negative charge. 2013 Pearson Education, Inc. Chapter 5, Section 1 129

Ionic Bonds An ionic bond occurs between metal and nonmetal ions. is a result of electron transfer. has a large electronegativity difference (1.8 or more). Examples: Atoms Electronegativity Type of Bond Difference 2013 Pearson Education, Inc. Chapter 5, Section 1 130

Determining Predominant Bond Type Look at the electronegativity values of atoms involved in bond Calculate electronegativity difference ( EN) If the bond is polar covalent, draw arrow in direction that e- cloud is pulled (more electronegative atom) Also use lower case Greek symbol for delta,, along with + or - sign 2013 Pearson Education, Inc. Chapter 5, Section 1 131

Electronegativity and Bond Types 2013 Pearson Education, Inc. Chapter 5, Section 1 132

Predicting Bond Types 2013 Pearson Education, Inc. Chapter 5, Section 1 133

Learning Check Use the electronegativity difference to identify the type of bond between the following atoms as nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K N B. N O C. Cl Cl D. B Cl 2013 Pearson Education, Inc. Chapter 5, Section 1 134

Solution Use the electronegativity difference to identify the type of bond between the following atoms as nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K N 2.2 ionic (I) B. N O 0.5 polar covalent (P) C. Cl Cl 0.0 nonpolar covalent (NP) D. B Cl 1.0 polar covalent (P) 2013 Pearson Education, Inc. Chapter 5, Section 1 135

Polar Molecules A polar molecule contains polar bonds. has a separation of positive and negative charge. called a dipole, indicated with + and. has dipoles that do not cancel. + H Cl NH 3 dipole Dipoles do not cancel. 2013 Pearson Education, Inc. Chapter 5, Section 1 136

Nonpolar Molecules A nonpolar molecule contains nonpolar bonds Cl Cl H H or has a symmetrical arrangement of polar bonds. 2013 Pearson Education, Inc. Chapter 5, Section 1 137

Guide to Determination of Polarity 2013 Pearson Education, Inc. Chapter 5, Section 1 138

Molecular Polarity, H 2 O Determine the polarity of the H 2 O molecule. Step 1 Determine if the bonds are polar covalent or nonpolar covalent. From the electronegativity table, O 3.5 and H 2.1 gives a difference of 1.4, which makes the O H bonds, polar covalent. 2013 Pearson Education, Inc. Chapter 5, Section 1 139

Molecular Polarity, H 2 O Determine the polarity of the H 2 O molecule. Step 2 If the bonds are polar covalent, draw the electron-dot formula and determine if the dipoles cancel or not. The four electron groups of oxygen are bonded to two H atoms. Thus, the H 2 O molecule has a net dipole, which makes it a polar molecule. 2013 Pearson Education, Inc. Chapter 5, Section 1 140

Polar Molecules A polar molecule contains polar bonds. has a separation of positive and negative charge. called a dipole, indicated with + and. has dipoles that do not cancel. + H Cl NH 3 dipole Dipoles do not cancel. 2013 Pearson Education, Inc. Chapter 5, Section 1 141

Learning Check Determine the shape of each of the following molecules and whether they are polar or nonpolar. Explain. 1. PBr 3 2. HBr 3. Br 2 4. SiBr 4 2013 Pearson Education, Inc. Chapter 5, Section 1 142

Solution Determine the shape of each of the following molecules and whether they are polar or nonpolar. Explain. 1. PBr 3 pyramidal; polar; dipoles don t cancel 2. HBr linear; polar; one polar bond (dipole) 3. Br 2 linear; nonpolar; nonpolar bond 4. SiBr 4 tetrahedral; nonpolar; dipoles cancel 2013 Pearson Education, Inc. Chapter 5, Section 1 143

General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 5 Compounds and Their Bonds 5.9 Attractive Forces in Compounds 2013 Pearson Education, Inc. Lectures 2013 Pearson Education, Inc. Chapter 5, Section 1 144

States of Matter The fundamental difference between states of matter is the distance between particles. 2013 Pearson Education, Inc. Chapter 5, Section 1 145

States of Matter Because in the solid and liquid states particles are closer together, we refer to them as condensed phases. 2013 Pearson Education, Inc. Chapter 5, Section 1 146

The States of Matter The state a substance is in at a particular temperature and pressure depends on two antagonistic entities: The kinetic energy of the particles The strength of the attractions between the particles 2013 Pearson Education, Inc. Chapter 5, Section 1 147

Ionic Compounds In ionic compounds, ionic bonds require large amounts of energy to break. hold positive and negative ions together. explain their high melting points. 2013 Pearson Education, Inc. Chapter 5, Section 1 148

What about covalent compounds? The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together. 2013 Pearson Education, Inc. Chapter 5, Section 1 149

Intermolecular Forces They are, however, strong enough to control physical properties such as the state a molecular compound will be in at room temperature, its melting and boiling point. 2013 Pearson Education, Inc. Chapter 5, Section 1 150

Intermolecular Forces In addition, they are responsible for the shapes of protein molecules, DNA, water s unique properties, the structure of the cell membrane, etc 2013 Pearson Education, Inc. Chapter 5, Section 1 151

Covalent Compounds In covalent compounds, the attractive forces between solid and liquid molecules are weaker than ionic bonds. require less energy to break. explain why their melting points are lower than ionic compounds. These attractive forces include dipole-dipole attractions, dispersion forces, and hydrogen bonding. 2013 Pearson Education, Inc. Chapter 5, Section 1 152

Intermolecular Forces They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities. 2013 Pearson Education, Inc. Chapter 5, Section 1 153

Dipole-Dipole Attractions In covalent compounds, polar molecules exert attractive forces between molecules called dipole-dipole attractions. dipole dipole forces 2013 Pearson Education, Inc. Chapter 5, Section 1 154

Dipole-Dipole Attractions, Hydrogen Bonds In covalent compounds, some polar molecules form strong dipole attractions called hydrogen bonds, which occur between the partially positive hydrogen atom of one molecule and a lone pair of electrons on a nitrogen, oxygen, or fluorine atom in another molecule. 2013 Pearson Education, Inc. Chapter 5, Section 1 155

Dispersion Forces Dispersion forces are weak attractions between nonpolar molecules. caused by temporary dipoles that develop when electrons are not distributed equally. Nonpolar molecules form attractions when they form temporary dipoles. 2013 Pearson Education, Inc. Chapter 5, Section 1 156

London Dispersion Forces While the electrons in the 1s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom. 2013 Pearson Education, Inc. Chapter 5, Section 1 157

London Dispersion Forces At that instant, then, the helium atom is polar, with an excess of electrons on the left side and a shortage on the right side. 2013 Pearson Education, Inc. Chapter 5, Section 1 158

London Dispersion Forces Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1. 2013 Pearson Education, Inc. Chapter 5, Section 1 159

London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole. 2013 Pearson Education, Inc. Chapter 5, Section 1 160

London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability. 2013 Pearson Education, Inc. Chapter 5, Section 1 161

Factors Affecting London Forces The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger dispersion forces than short, fat ones (like neopentane). This is due to the increased surface area in n-pentane. 2013 Pearson Education, Inc. Chapter 5, Section 1 162

Factors Affecting London Forces The strength of dispersion forces tends to increase with increased molecular weight. Larger atoms have larger electron clouds, which are easier to polarize. 2013 Pearson Education, Inc. Chapter 5, Section 1 163

Which Have a Greater Effect: Dipole-Dipole Interactions or Dispersion Forces? If two molecules are of comparable size and shape, dipole-dipole interactions will likely be the dominating force. If one molecule is much larger than another, dispersion forces will likely determine its physical properties. 2013 Pearson Education, Inc. Chapter 5, Section 1 164

Comparison of Bonding and Attractive Forces 2013 Pearson Education, Inc. Chapter 5, Section 1 165

Intermolecular Forces Affect Many Physical Properties The strength of the attractions between particles can greatly affect the properties of a substance or solution. 2013 Pearson Education, Inc. Chapter 5, Section 1 166

Melting Points and Attractive Forces The stronger the attractive force between ions or molecules, the higher the melting points. Ionic compounds, have the strongest attractive force and, therefore the highest melting points. Covalent molecules have less attractive forces than ionic compounds and, therefore lower melting points. 2013 Pearson Education, Inc. Chapter 5, Section 1 167

Melting Points and Attractive Forces The attractive forces between covalent molecules vary in magnitude; the stronger the attractive force, the higher its melting point. Hydrogen bonds are the strongest type of dipole dipole attractions, requiring the most energy to break, followed by dipole dipole forces. Dispersion forces are the weakest, requiring even less energy to break them, and therefore have lower melting points than hydrogen bonds and dipole dipole forces. 2013 Pearson Education, Inc. Chapter 5, Section 1 168

Melting Points of Selected Substances 2013 Pearson Education, Inc. Chapter 5, Section 1 169

Learning Check Identify the main type of attractive forces for each of the following compounds: ionic bonds, dipole dipole, hydrogen bonds or dispersion. 1. NCl 3 2. H 2 O 3. Br 2 4. KCl 5. NH 3 2013 Pearson Education, Inc. Chapter 5, Section 1 170

Solution Identify the main type of attractive forces for each of the following compounds: ionic bonds, dipole dipole, hydrogen bonds or dispersion. 1. NCl 3 dipole dipole 2. H 2 O hydrogen bonds 3. Br 2 dispersion 4. KCl ionic bonds 5. NH 3 hydrogen bonds 2013 Pearson Education, Inc. Chapter 5, Section 1 171