Solid State Lab Report Due

1
Announcements General Info
Solid State Lab Report Due Exam 2 Workbook 2 -
due Thursday (11/01) No late workbooks accepted
Exam 2 Friday 11/02 Chapters 7, 8, 9 12.6
(no conductivity) review after Ch.10 on
Thursday Lecture Today Chapter 9
2
Bonding Models
Bonding Theories

• Bonding is the way atoms ______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

3
Types of Bonding
Van der Waals (dispersion/London) forces are the
intermolecular attractions between all particles
as a result of instantaneous polarizations of
their electron clouds. Hydrogen Bonds are
special bonds that arise between molecules that
have a hydrogen atom and molecules that have lone
pair electrons (typically N, O, or F). Ionic
Bonds are held together by electrostatic
attraction ____________. They form between
Covalent Bonds form between atoms that share
their electrons. These are typically formed
between Metallic Bonds are the bonds between
two or more metallic elements that share their
mobile valence electrons. They are based on the
attraction between metal ions and
4
Three Models of Chemical Bonding
5
Representing Valence Electrons with Dots
Lewis Dot Structures

• also known as electron dot symbols
• Use symbol of element to represent
• Use dots around the symbol to represent
• Remember that elements in the same group have the
  same number of valence electrons therefore their
  Lewis dot symbols will look alike

6
Lewis electron-dot symbols for elements in
Periods 2 and 3
Figure 9.3
The number of unpaired dots shows
Ionization Energy - the energy (in KJ) required
to remove completely one mole of electrons from
one mole of gaseous atoms or ions. Electron
affinity - the energy change (in KJ) accompanying
the addition of one mole of electrons to one mole
of gaseous atoms or ions.
7
Ionic Bonds.
Formed betwee The metal The
nonmeta The ionic bond results from to -
attraction larger charge stronger
attraction smaller ion stronger
attraction Lewis dot structures allow us to
predict the correct formulas of ionic compounds
8
Lewis Structures for Ionic Compounds Electrons
Transferred

• 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

9
Lewis Structures for Ionic Compounds Electrons
Transferred
Using Lewis Theory to Predict Chemical Formulas
of Ionic Compounds
Predict the formula of the compound that forms
between calcium and chlorine
Draw the Lewis dot symbols of the elements

CaCl2
10
Ionic Bonds

• An ionic bond is formed when

• Energy must be input to remove an electron from a
  metal (IE is positive). Generally, the energy
  released when the nonmetal accepts an electron
  (EA is negative) does not compensate for the IE
  (e.g. IE1 of Li 520 kJ/mol EA of F 328
  kJ/mol).

11

• IE and EA are for adding/removing an electron
  to/from an atom in the gaseous state.
• Much energy is released on forming the solid
  state structure the reverse of this is called
  the _________, the driving force for the
  formation of ionic compounds.
• _____________ is the enthalpy change that
  accompanies the separation of 1 mol of ionic
  solid into gaseous ions.
• _____________ can be calculated using Hesss law,
  via a Born-Haber Cycle. The Born-Haber cycle
  breaks down the overall heat of formation
  reaction into the individual steps required for
  the overall process to occur.

12
The Born-Haber Cycle for Lithium Fluoride
Figure 9.6
13
Calculating Lattice Energy

• Step 1 Convert elements to atoms in the gas
  state
• e.g. for Li, Li (s) ? Li (g) DH1
  DHatomization
• for F, 1/2 F2 (g) ? F (g) DH2 1/2 (Bond
  Energy)
• Step 2 Electron transfer to form (isolated) ions
• Li (g) ? Li (g) e DH3 IE1
• F (g) e ? F (g) DH4 EA1
• Step 3 Ions come together to form solid
• Li (g) F (g) ? LiF (s) DH5 Lattice
  Energy
• Overall Li (s) 1/2 F2 (g) ? LiF (s) DH
  DHf S(DH15)

14
Periodic Trends in Lattice Energy
Coulombs Law - the electrostatic force
associated with two charges, A and B, is directly
proportional to the product of their magnitudes
and inversely proportional to the square of the
distance between them.
charge A X charge B
electrostatic force a
distance2
charge A X charge B
or electrostatic energy a
distance
(since energy force X distance)
15
Covalent Bonds

• often found between
• sharing pairs of electrons

A attractive/repulsive interactions between the
two atoms B contour map of electron density C
topographical map of electron density
16
Covalent Lewis Structures Electrons Shared

• Bonding Lone Pair Electrons
• Electrons that are shared by atoms are called
• Electrons that are not shared by atoms but belong
  to a particular atom are called___________.
  These are also known as nonbonding pairs.

O S O







17
Types of Bonds and Bond Order
The bond order is the number of electron pairs
being shared by any pair of bonded atoms. The
higher the bond order, the stronger the bond
(higher bond energy), and the shorter the
bond Within a series of similar molecules, bond
length increases with atomic radius A single
bond has a bond order of 1 - single bonding
electron pair two atoms share two electrons A
double bond has a bond order of 2 - two bonding
electron pairs two atoms share four
electrons A triple bond has a bond order of 3 -
three bonding electron pairs two atoms share
six electrons
18
Bond Energy and Chemical Change
The bond energy (also called bond enthalpy or
bond strength) is the enthalpy change
accompanying the breakage of a given bond in a
mole of gaseous atoms. Bond breakage is an
endothermic process, so ?H0bond breaking gt
0 AB(g) ? A(g) B(g) Bond formation is an
exothermic process, so the ?H0bond forming lt
0 A(g) B(g) ? AB(g) ?H0reaction
??H0reactant bonds broken ??H0product bonds
formed or ?H0reaction ?BEreactant bonds
broken - ?BEproduct bonds formed
19
Electronegativity and Bond Polarity
Bond Polarity

• Bonding between unlike atoms results in unequal
  sharing of the electrons
• The result is bond polarity

20
Electronegativity and Polarity
Electronegativity

• Measure of
• Increases across period (left to right)
• Decreases down group (top to bottom)
• Larger difference in electronegativity
• negative end toward more electronegative atom

21
Electronegativity and Polarity
22
Electronegativity and Polarity
23
Electronegativity and Polarity

• If difference in electronegativity between bonded
  atoms is 0, the bond is
• If difference in electronegativity between bonded
  atoms is 0.1 to 0.3, the bond is
• If difference in electronegativity between bonded
  atoms 0.4 to 1.9, the bond is
• If difference in electronegativity between bonded
  atoms larger than or equal to 2.0, the bond is
• These values are slightly different from your
  textbook

24
Electronegativity and Polarity
Bond Polarity
3.0-3.0 0.0
4.0-2.1 1.9
3.0-0.9 2.1
covalent
ionic
non polar
polar
4.0
0
0.4
2.0
Electronegativity Difference
25
Electronegativity and Polarity
Dipole Moments

• A dipole is a material with partially positively
  and negatively charged ends
• Polar bonds or molecules have one end slightly
  positive, d and the other slightly negative, d-
• Dipole Moment, m, is a measure of the size of the
  polarity
• measured in Debyes, D

26
Interparticle Forces
Physical Behavior
Particles
Examples (mp,0C)
Type
Atomic
Group 8A(18) Ne-249 to Rn-71
Soft, very low mp, poor thermal electrical
conductors
Dispersion
Atoms
Molecular
Molecules
Dispersion, dipole-dipole, H bonds
Fairly soft, low to moderate mp, poor thermal
electrical conductors
Nonpolar - O2-219, C4H10-138, Cl2 -101,
C6H14-95 Polar - SO2-73, CHCl3-64,
HNO3-42, H2O0.0
Ionic
Positive negative ions
Ion-ion attraction
Hard brittle, high mp, good thermal
electrical conductors when molten
NaCl 801 CaF2 1423 MgO 2852
Metallic
Atoms
Metallic bond
Soft to hard, low to very high mp, excellent
thermal and electrical conductors, malleable and
ductile
Na 97.8 Zn 420 Fe 1535
Network
Atoms
Covalent bond
Very hard, very high mp, usually poor thermal and
electrical conductors
SiO2 (quartz)1610 C(diamond)4000