1. Chapter 2: Atomic Structure & Interatomic Bonding
ISSUES TO ADDRESS...
• What promotes bonding?
• What types of bonds are there?
• What properties are inferred from bonding?

2. Atomic Structure (Freshman Chem.)
atom – electrons – x kg  protons neutrons
atomic number = # of protons in nucleus of atom = # of electrons in neutral species
A [=] atomic mass unit = amu = 1/12 mass of 12C   Atomic wt = wt of x 1023 molecules or atoms   1 amu/atom = 1 g/mol
C H etc.
} 1.67 x kg

3. Atomic Structure Some of the following properties
Chemical
Electrical
Thermal
Optical
are determined by electronic structure

4. Electronic Structure
Electrons have wavelike and particulate properties.
Two of the wavelike characteristics are
electrons are in orbitals defined by a probability.
each orbital at discrete energy level is determined by quantum numbers.  
Quantum # Designation
n = principal (energy level-shell) K, L, M, N, O (1, 2, 3, etc.)
l = subsidiary (orbitals) s, p, d, f (0, 1, 2, 3,…, n -1)
ml = magnetic 1, 3, 5, 7 (-l to +l)
ms = spin ½, -½

5. Electron Energy States
Electrons...
• have discrete energy states
• tend to occupy lowest available energy state. 1s 2s 2p
K-shell n = 1
L-shell n = 2 3s 3p
M-shell n = 3 3d 4s 4p 4d
Energy
N-shell n = 4
Adapted from Fig. 2.6, Callister & Rethwisch 9e. (From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering, p. 22. Copyright © 1976 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.)

6. SURVEY OF ELEMENTS • Most elements: Electron configuration not stable.
... 1s 2 2s 2p 6 3s 3p 3d 10 4s 4p
Atomic # 18 36
Element 1
Hydrogen
Helium 3
Lithium 4
Beryllium 5
Boron
Carbon
Neon 11
Sodium 12
Magnesium 13
Aluminum
Argon
Krypton
Adapted from Table 2.2, Callister & Rethwisch 9e.
• Why? Valence (outer) shell usually not filled completely.

7. Electron Configurations
Valence electrons – those in unfilled shells
Filled shells more stable
Valence electrons are most available for bonding and tend to control the chemical properties
example: C (atomic number = 6)
1s2 2s2 2p2
valence electrons

8. Electronic Configurations26
1s2 2s2 2p6 3s2 3p6
3d 6 4s2
valence
electrons
ex: Fe - atomic # = 1s 2s 2p
K-shell n = 1
L-shell n = 2 3s 3p
M-shell n = 3 3d 4s 4p 4d
Energy
N-shell n = 4
Adapted from Fig. 2.6, Callister & Rethwisch 9e. (From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering, p. 22. Copyright © 1976 by John Wiley & Sons, New York. Reprinted by permission of John Wiley & Sons, Inc.)

9. The Periodic Table • Columns: Similar Valence Structure give up 1e-
inert gases
accept 1e-
accept 2e- O Se Te Po At I Br He Ne Ar Kr Xe Rn F Cl S Li Be H Na Mg Ba Cs Ra Fr Ca K Sc Sr Rb Y
Adapted from Fig. 2.8, Callister & Rethwisch 9e.
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.

10. Electronegativity • Ranges from 0.9 to 4.1,
• Large values: tendency to acquire electrons.
Smaller electronegativity
Larger electronegativity

11. Ionic bond – metal + nonmetal
donates accepts electrons electrons  
Dissimilar electronegativities  
ex: MgO Mg 1s2 2s2 2p6 3s O 1s2 2s2 2p4
[Ne] 3s2 
Mg2+ 1s2 2s2 2p O2- 1s2 2s2 2p6
[Ne] [Ne]

12. Ionic Bonding - + • Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
Na (metal)
unstable
Cl (nonmetal)
electron + -
Coulombic
Attraction
Na (cation)
stable
Cl (anion)

13. Ionic Bonding Energy – minimum energy most stable r A B EN = EA + ER =
Energy balance of attractive and repulsive terms r A n B
EN = EA + ER = + -
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
Adapted from Fig. 2.10(b), Callister & Rethwisch 9e.

14. Examples: Ionic Bonding
• Predominant bonding in Ceramics
NaCl
MgO
CaF 2
CsCl
Give up electrons
Acquire electrons

15. Covalent Bonding similar electronegativity  share electrons
bonds determined by valence – s & p orbitals dominate bonding
Example: H2 H2
Each H: has 1 valence e-,
needs 1 more H H
Electronegativities
are the same.
shared 1s electron
shared 1s electron
from 1st hydrogen
atom
from 2nd hydrogen
atom
Fig. 2.12, Callister & Rethwisch 9e.

16. Bond Hybrization Carbon can form sp3 hybrid orbitals
Fig. 2.14, Callister & Rethwisch 9e. (Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.)
Fig. 2.13, Callister & Rethwisch 9e.

17. Covalent Bonding: Carbon sp3
Example: CH4
C: has 4 valence e-,
needs 4 more
H: has 1 valence e-,
needs 1 more
Electronegativities of C and H
are comparable so electrons
are shared in covalent bonds.
Fig. 2.15, Callister & Rethwisch 9e.
(Adapted from J.E. Brady and F. Senese, Chemistry: Matter and Its Changes, 4th edition. Reprinted with permission of John Wiley and Sons, Inc.)

18. Primary Bonding Metallic Bond -- delocalized as electron cloud
Ionic-Covalent Mixed Bonding
% ionic character =  
where XA & XB are Pauling electronegativities %)
100 ( x
Ex: MgO XMg = XO = 3.5

19. Secondary Bonding + - Arises from interaction between dipoles
• Fluctuating dipoles
asymmetric electron
clouds + -
secondary
bonding H 2
ex: liquid H
Adapted from Fig. 2.20, Callister & Rethwisch 9e.
• Permanent dipoles-molecule induced + -
-general case:
secondary
bonding
Adapted from Fig. 2.22,
Callister & Rethwisch 9e. Cl Cl
-ex: liquid HCl
secondary H H
bonding
secondary bonding
-ex: polymer
secondary bonding

20. Summary: Bonding Type Bond Energy Comments Ionic Large!
Nondirectional (ceramics)
Covalent
Variable
Directional
(semiconductors, ceramics
polymer chains)
large-Diamond
small-Bismuth
Metallic
Variable
large-Tungsten
Nondirectional (metals)
small-Mercury
Secondary
smallest
Directional
inter-chain (polymer)
inter-molecular

21. Properties From Bonding: Tm
• Bond length, r
• Melting Temperature, Tm r o
Energy r
• Bond energy, Eo Eo =
“bond energy”
Energy r o
unstretched length
smaller Tm
larger Tm
Tm is larger if Eo is larger.

22. Properties From Bonding: α
• Coefficient of thermal expansion, α Δ L
length, o
unheated, T 1
heated, T 2
coeff. thermal expansion Δ L = α ( T - T ) 2 1 L o
• α ~ symmetric at ro r o
smaller α
larger α
Energy
unstretched length Eo
α is larger if Eo is smaller.

23. Summary: Primary Bonds
Ceramics
Large bond energy
large Tm
large E
small α
(Ionic & covalent bonding):
Metals
(Metallic bonding):
Variable bond energy
moderate Tm
moderate E
moderate α
Polymers
(Covalent & Secondary):
Directional Properties
Secondary bonding dominates
small Tm
small E
large α
secondary bonding

24. ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems: