Introductory Chemistry, 2nd Edition Nivaldo Tro

Introductory Chemistry, 2nd Edition Nivaldo Tro

Introductory Chemistry, 2nd Edition Nivaldo Tro Chapter 10 Chemical Bonding Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2006, Prentice Hall Bonding Theories bonding is the way atoms attach to make molecules an understanding of how and why atoms attach together in the manner they do is central to chemistry chemists have an understanding of bonding that allows them to: 1) predict the shapes of molecules and properties of substances based on the bonding within the molecules 2) design and build molecules with particular sets of chemical and physical properties Tro's Introductory Chemistry, Chapte

r 10 2 Lewis Symbols of Atoms also known as electron dot symbols use symbol of element to represent nucleus and inner electrons use dots around the symbol to represent valence electrons put one electron on each side first, then pair remember that elements in the same group have the same number of valence electrons; therefore their Lewis dot symbols will look alike Li Be B

C N O: Tro's Introductory Chemistry, Chapte r 10 :F: :Ne:

3 Lewis Bonding Theory atoms bond because it results in a more stable electron configuration atoms bond together by either transferring or sharing electrons so that all atoms obtain an outer shell with 8 electrons Octet Rule there are some exceptions to this rule the key to remember is to try to get an electron configuration like a noble gas Tro's Introductory Chemistry, Chapte r 10 4 Lewis Symbols of Ions Cations have Lewis symbols without valence electrons Lost in the cation formation Anions have Lewis symbols with 8 valence electrons Electrons gained in the formation of the anion

Li Li +1 :F: [:F:]-1 Tro's Introductory Chemistry, Chapte r 10 5 Ionic Bonds

metal to nonmetal metal loses electrons to form cation nonmetal gains electrons to form anion ionic bond results from + to - attraction larger charge = stronger attraction smaller ion = stronger attraction Lewis Theory allow us to predict the correct formulas of ionic compounds Tro's Introductory Chemistry, Chapte r 10 6 Example 10.3 - Using Lewis Theory to Predict Chemical Formulas of Ionic Compounds Predict the formula of the compound that forms between calcium and chlorine.

Ca : Cl : Ca2+ Tro's Introductory Chemistry, Chapte r 10 Cl Cl Transfer all the valance electrons from the metal to the nonmetal, adding more of each atom as you go, until all electrons are lost

from the metal atoms and all nonmetal atoms have 8 electrons Cl Ca Draw the Lewis dot symbols of the elements : Cl : CaCl2 7 Covalent Bonds

often found between two nonmetals typical of molecular species atoms bonded together to form molecules strong attraction sharing pairs of electrons to attain octets molecules generally weakly attracted to each other observed physical properties of molecular substance due to these attractions Tro's Introductory Chemistry, Chapte r 10 8 Single Covalent Bonds two atoms share one pair of electrons 2 electrons one atom may have more than one single bond H

F H O H F H F

F O F F

Tro's Introductory Chemistry, Chapte r 10 9 Double Covalent Bond two atoms sharing two pairs of electrons 4 electrons shorter and stronger than single bond O O O O

O O Tro's Introductory Chemistry, Chapte r 10 10 Triple Covalent Bond two atoms sharing 3 pairs of electrons 6 electrons N

N N shorter and stronger than single or double bond N N N Tro's Introductory Chemistry, Chapte r 10 11

Bonding & Lone Pair Electrons Electrons that are shared by atoms are called bonding pairs Electrons that are not shared by atoms but belong to a particular atom are called lone pairs also known as nonbonding pairs Bonding Pairs O S O Tro's Introductory Chemistry, Chapte r 10 Lone Pairs 12 Polyatomic Ions The polyatomic ions are attracted to opposite ions by ionic bonds

Form crystal lattices Atoms in the polyatomic ion are held together by covalent bonds Tro's Introductory Chemistry, Chapte r 10 13 Lewis Formulas of Molecules shows pattern of valence electron distribution in the molecule useful for understanding the bonding in many compounds allows us to predict shapes of molecules allows us to predict properties of molecules and how they will interact together Tro's Introductory Chemistry, Chapte r 10 14 Lewis Structures

some common bonding patterns C = 4 bonds & 0 lone pairs 4 bonds = 4 single, or 2 double, or single + triple, or 2 single + double N = 3 bonds & 1 lone pair, O = 2 bonds & 2 lone pairs, H and halogen = 1 bond, Be = 2 bonds & 0 lone pairs, B = 3 bonds & 0 lone pairs B C N O Tro's Introductory Chemistry, Chapte r 10 F 15 Writing Lewis Structures

for Covalent Molecules 1) Attach the atoms together in a skeletal structure most metallic element generally central halogens and hydrogen are generally terminal many molecules tend to be symmetrical in oxyacids, the acid hydrogens are attached to an oxygen 2) Calculate the total number of valence electrons available for bonding use group number of periodic table Tro's Introductory Chemistry, Chapte r 10 16 Writing Lewis Structures for Covalent Molecules 3) Attach atoms with pairs of electrons and subtract electrons used from total

bonding electrons 4) Add remaining electrons in pairs to complete the octets of all the atoms remember H only wants 2 electrons dont forget to keep subtracting from the total complete octets on the terminal atoms first, then work toward central atoms Tro's Introductory Chemistry, Chapte r 10 17 Writing Lewis Structures for Covalent Molecules 5) If there are not enough electrons to complete the octet of the central atom, bring pairs of electrons from an attached atom in to share with the central atom until it has an octet try to follow common bonding patterns Tro's Introductory Chemistry, Chapte r 10

18 Example HNO3 1) Write skeletal structure since this is an oxyacid, H on outside attached to one of the Os; N is central O H O N O 2) Count Valence Electrons and Subtract Bonding Electrons from Total N=5 H=1 O3 = 36 = 18 Total = 24 eTro's Introductory Chemistry, Chapte r 10 Electrons Start 24 Used 8 Left 16 19

Example HNO3 3) Complete Octets, outside-in H is already complete with 2 1 bond : O : H O N O 4) Re-Count Electrons Electrons Start 24 Used 8 Left 16

Electrons Start 16 Used 16 Left 0 Tro's Introductory Chemistry, Chapte r 10 20 N=5 H=1 O3 = 36 = 18 Total = 24 e- : Example HNO3 5) If central atom does not have octet, bring in electron pairs from outside atoms to share :

O : follow common bonding patterns if H O N O possible : O | H O N : O :

Tro's Introductory Chemistry, Chapte r 10 : 21 Example 10.4: Writing Lewis Structures for Covalent Compounds Example: Write the Lewis structure of CO2. Tro's Introductory Chemistry, Chapte r 10 23 Example: Write the Lewis structure of CO2.

Write down the given quantity and its units. Given: CO2 Tro's Introductory Chemistry, Chapte r 10 24 Example: Write the Lewis structure of CO2. Information Given: CO2 Write down the quantity to find and/or its units. Find: Lewis structure Tro's Introductory Chemistry, Chapte r 10

25 Example: Write the Lewis structure of CO2. Design a Solution Map. formula of compound skeletal structure Information Given: CO2 Find: Lewis structure Lewis structure count and distribute electrons Tro's Introductory Chemistry, Chapte r 10 26

Example: Write the Lewis structure of CO2. Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Apply the Solution Map. write skeletal structure least metallic atom central H terminal symmetry O C O Tro's Introductory Chemistry, Chapte r 10 27 Example:

Write the Lewis structure of CO2. Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Apply the Solution Map. Count and Distribute the Valence Electrons count valence electrons O C O 1A 2A 8A 3A4A 5A6A 7A C O total

Tro's Introductory Chemistry, Chapte r 10 C=4 O=26 CO2 = 16 28 Example: Write the Lewis structure of CO2. Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Apply the Solution Map. Count and Distribute the Valence Electrons attach atoms O C O

total C=4 O=26 CO2 = 16 start = 16 euse = 4 eleft = 12 eTro's Introductory Chemistry, Chapte r 10 29 Example: Write the Lewis structure of CO2. Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Apply the Solution Map. C=4 Count and Distribute the Valence Electrons O=26

complete octets total CO2 = 16 outside atoms first start = 16 euse = 4 e left = 12 e- :O C O : Tro's Introductory Chemistry, Chapte r 10 start = 12 euse = 12 eleft = 0 e30 Example: Write the Lewis structure of CO2.

Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Apply the Solution Map. Count and Distribute the Valence Electrons complete octets if not enough electrons to complete octet of central atom, bring in pairs of electrons from attached atom to make multiple bonds :O C O

: : O C O : Tro's Introductory Chemistry, Chapte r 10 start = 12 euse = 12 eleft = 0 e31 Example: Write the Lewis structure of CO2. Information Given: CO2 Find: Lewis structure SM: formula skeletal electron distribution Lewis Check total Start

C = 4 eO = 2 6 eCO2 = 16 e- End bonding = 4 2 elone pairs = 4 2 etotal CO2 = 16 e- : O C O : The skeletal structure is symmetrical. All the electrons are accounted for. Tro's Introductory Chemistry, Chapte r 10 32 Writing Lewis Structures for Polyatomic Ions the procedure is the same, the only difference is in counting the valence electrons for polyatomic cations, take away one electron from the total for each positive

charge for polyatomic anions, add one electron to the total for each negative charge Tro's Introductory Chemistry, Chapte r 10 33 Example NO31) Write skeletal structure N is central because it is the most metallic O O N O 2) Count Valence Electrons and Subtract Bonding Electrons from Total N=5 O3 = 36 = 18 (-) = 1 Total = 24 e- Tro's Introductory Chemistry, Chapte r 10

Electrons Start 24 Used 6 Left 18 34 Example NO33) Complete Octets, outside-in : : O : O N O 4) Re-Count Electrons

Electrons Start 24 Used 6 Left 18 Electrons Start 18 Used 18 Left 0 Tro's Introductory Chemistry, Chapte r 10 35 N=5 O3 = 36 = 18 (-) = 1 Total = 24 e- : Example NO35) If central atom does not have octet, bring in electron pairs from outside atoms to share

follow common bonding patterns if possible : : O : O N O : : O

| O N : O : Tro's Introductory Chemistry, Chapte r 10 : 36 Exceptions to the Octet Rule H & Li, lose one electron to form cation Li now has electron configuration like He H can also share or gain one electron to have configuration like He Be shares 2 electrons to form two single bonds

B shares 3 electrons to form three single bonds expanded octets for elements in Period 3 or below using empty valence d orbitals some molecules have odd numbers of electrons NO : N O : Tro's Introductory Chemistry, Chapte r 10 37 Resonance we can often draw more than one valid Lewis structure for a molecule or ion in other words, no one Lewis structure can adequately describe the actual structure of the molecule the actual molecule will have some characteristics of all the valid Lewis

structures we can draw Tro's Introductory Chemistry, Chapte r 10 38 Resonance Lewis structures often do not accurately represent the electron distribution in a molecule Lewis structures imply that O3 has a single (147 pm) and double (121 pm) bond, but actual bond length is between, (128 pm) Real molecule is a hybrid of all possible Lewis structures Resonance stabilizes the molecule maximum stabilization comes when resonance forms contribute equally to the hybrid + O O O O

O Tro's Introductory Chemistry, Chapte r 10 + O 39 Drawing Resonance Structures 1. draw first Lewis structure that maximizes octets 2. move electron pairs from outside atoms to share with central atoms 3. if central atom 2nd row, only move in electrons if you can move out electron pairs from multiple bond O O

O Tro's Introductory Chemistry, Chapte r 10 N O N O O 40

Molecular Geometry Molecules are 3-dimensional objects We often describe the shape of a molecule with terms that relate to geometric figures These geometric figures have characteristic corners that indicate the positions of the surrounding atoms with the central atom in the center of the figure The geometric figures also have characteristic angles that we call bond angles Tro's Introductory Chemistry, Chapte r 10 41 Some Geometric Figures Linear 180 2 atoms on opposite sides of central atom 180 bond angles Trigonal Planar

3 atoms form a triangle around the central atom Planar 120 bond angles 120 Tetrahedral 4 surrounding atoms form a tetrahedron around the central atom 109.5 bond angles Tro's Introductory Chemistry, Chapte r 10 109.5 42 Predicting Molecular Geometry VSEPR Theory Valence Shell Electron Pair Repulsion The shape around the central atom(s) can be predicted by assuming that the areas of electrons on the central atom will try to get

as far from each other as possible areas of negative charge will repel each other Tro's Introductory Chemistry, Chapte r 10 43 Areas of Electrons Each Bond counts as 1 area of electrons single, double or triple all count as 1 area Each Lone Pair counts as 1 area of electrons Even though lone pairs are not attached to other atoms, they do occupy space around the central atom Lone pairs take up slightly more space than bonding pairs Effects bond angles Tro's Introductory Chemistry, Chapte r 10 44 Linear Shapes

Linear 2 areas of electrons around the central atom, both bonding :O C O : Or two atom molecule as trivial case 180 Bond Angles Tro's Introductory Chemistry, Chapte r 10 45

Trigonal Shapes Trigonal 3 areas of electrons around the central atom 120 bond angles All Bonding = trigonal planar 2 Bonding + 1 Lone Pair = bent Tro's Introductory Chemistry, Chapte r 10 H C O H 46 : Tetrahedral Shapes Tetrahedral 4 areas of electrons around the central atom

109.5 bond angles All Bonding = tetrahedral 3 Bonding + 1 Lone Pair = trigonal pyramid 2 Bonding + 2 Lone Pair = bent Tro's Introductory Chemistry, Chapte r 10 H H C H H 47 Tetrahedral Derivatives H N H H H O H

Tro's Introductory Chemistry, Chapte r 10 48 Molecular Geometry: Linear Electron Groups Around Central Atom = 2 Bonding Groups = 2 Lone Pairs = 0 Electron Geometry = Linear Angle between Electron Groups = 180 Tro's Introductory Chemistry, Chapte r 10 49

Molecular Geometry: Trigonal Planar Electron Groups Around Central Atom = 3 Bonding Groups = 3 Lone Pairs = 0 Electron Geometry = Trigonal Planar Angle between Electron Groups = 120 50 Molecular Geometry: Bent Electron Groups Around Central Atom = 3 Bonding Groups = 2 Lone Pairs = 1

Electron Geometry = Trigonal Planar Angle between Electron Groups = 120 Tro's Introductory Chemistry, Chapte r 10 51 Molecular Geometry: Tetrahedral Electron Groups Around Central Atom = 4 Bonding Groups = 4 Lone Pairs = 0 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5 52 Molecular Geometry: Trigonal Pyramid

Electron Groups Around Central Atom = 4 Bonding Groups = 3 Lone Pairs = 1 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5 53 Molecular Geometry: Bent Electron Groups Around Central Atom = 4 Bonding Groups = 2 Lone Pairs = 2 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5

Tro's Introductory Chemistry, Chapte r 10 54 Bond Polarity bonding between unlike atoms results in unequal sharing of the electrons one atom pulls the electrons in the bond closer to its side one end of the bond has larger electron density than the other the result is bond polarity the end with the larger electron density gets a partial negative charge and the end that is electron deficient gets a partial positive charge H Cl Tro's Introductory Chemistry, Chapte r 10

55 Electronegativity measure of the pull an atom has on bonding electrons increases across period (left to right) decreases down group (top to bottom) larger difference in electronegativity, more polar the bond negative end toward more electronegative atom + H F - Tro's Introductory Chemistry, Chapte r 10 56

Electronegativity 2.1 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.9 1.2 1.5 1.8 2.1 2.5 3.0 0.8 1.0 1.3 1.5 1.6 1.6 1.5 1.8 1.8 1.8 1.9 1.6 1.6 1.8 2.0 2.4 2.8 0.8 1.0 1.2 1.4 1.6 1.8 1.9 2.2 2.2 2.2 1.9 1.7 1.7 1.8 1.9 2.1 2.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.2 2.2 2.2 2.4 1.9 1.8 1.8 1.9 2.0 2.2 0.7 0.9 1.1 Tro's Introductory Chemistry, Chapte r 10 57 Electronegativity Tro's Introductory Chemistry, Chapte r 10

58 Electronegativity & Bond Polarity If difference in electronegativity between bonded atoms is 0, the bond is pure covalent equal sharing If difference in electronegativity between bonded atoms is 0.1 to 0.3, the bond is nonpolar covalent If difference in electronegativity between bonded atoms 0.4 to 1.9, the bond is polar covalent If difference in electronegativity between bonded atoms larger than or equal to 2.0, the bond is ionic 59 Bond Polarity 3.0-3.0 = 0.0 4.0-2.1 = 1.9 covalent

non polar 0 3.0-0.9 = 2.1 ionic polar 0.4 2.0 Electronegativity Difference Tro's Introductory Chemistry, Chapte r 10 4.0 60 Dipole Moments a dipole is a material with positively and

negatively charged ends polar bonds or molecules have one end slightly positive, +; and the other slightly negative, not full charges, come from nonsymmetrical electron distribution Dipole Moment, , is a measure of the size of the polarity measured in Debyes, D Tro's Introductory Chemistry, Chapte r 10 61 Polarity of Molecules in order for a molecule to be polar it must 1) have polar bonds electronegativity difference - theory bond dipole moments - measured 2) have an unsymmetrical shape vector addition polarity effects the intermolecular forces of attraction Tro's Introductory Chemistry, Chapte

r 10 62 :O O H H polar bonds, and unsymmetrical shape causes molecule to be polar C O : polar bonds,

but nonpolar molecule because pulls cancel Tro's Introductory Chemistry, Chapte r 10 63 Cl Cl Cl Cl C H H Cl C Cl CH2Cl2

= 2.0 D CCl4 = 0.0 D Tro's Introductory Chemistry, Chapte r 10 64 Adding Dipole Moments 65 Example 10.11: Determining if a Molecule is Polar Example: Determine if NH3 is polar. Tro's Introductory Chemistry, Chapte r 10 67 Example:

Determine if NH3 is polar. Write down the given quantity and its units. Given: NH3 Tro's Introductory Chemistry, Chapte r 10 68 Example: Determine if NH3 is Polar. Information Given: NH3 Write down the quantity to find and/or its units. Find: if Polar

Tro's Introductory Chemistry, Chapte r 10 69 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar Design a Solution Map. formula of compound molecular polarity Lewis Structure bond polarity & molecular shape

Tro's Introductory Chemistry, Chapte r 10 70 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Draw the Lewis Structure write skeletal structure H N H H

Tro's Introductory Chemistry, Chapte r 10 71 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Draw the Lewis Structure count valence electrons H N H

total N=5 H=31 NH3 = 8 H Tro's Introductory Chemistry, Chapte r 10 72 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Draw the Lewis Structure attach atoms

H N H H Tro's Introductory Chemistry, Chapte r 10 total N=5 H=31 NH3 = 8 start use left 8 e6 e2 e73 Example:

Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Draw the Lewis Structure complete octets H N H H Tro's Introductory Chemistry, Chapte r 10 total

N=5 H=31 NH3 = 8 start use left 2 e2 e0 e74 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Determine if Bonds are Polar H

N H H Tro's Introductory Chemistry, Chapte r 10 Electronegativity N = 3.0 H = 2.1 3.0 2.1 = 0.9 polar covalent 75 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity

& Shape Molecule Polarity Apply the Solution Map. Determine Shape of Molecule H N H 4 areas of electrons around N; H 3 bonding areas 1 lone pair N H H H shape = trigonal pyramid

Tro's Introductory Chemistry, Chapte r 10 76 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Apply the Solution Map. Determine Molecular Polarity bonds = polar shape = trigonal pyramid N H H

H molecule = polar Tro's Introductory Chemistry, Chapte r 10 77 Example: Determine if NH3 is Polar. Information Given: NH3 Find: if Polar SM: formula Lewis Polarity & Shape Molecule Polarity Check. H total N=5 H=31

NH3 = 8 bonding = 3 2 elone pairs = 1 2 etotal NH3 = 8 e- N H bonds = polar shape = trigonal pyramid H H N H H The Lewis structure is correct. The bonds molecule = polar are polar and the shape is unsymmetrical, so it should be polar.

Tro's Introductory Chemistry, Chapte r 10 78

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