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  _______ neutrons
atomic number = # of protons in nucleus of atom = # of electrons in ______ species
A [=] atomic mass unit = ____ = 1/12 mass of 12C   Atomic wt = wt of ___________ molecules or atoms   1 amu/atom = 1 g/mol
C H etc.
} ____________

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

4. Electronic Structure
Electrons have wavelike and particulate properties.
Two of the wavelike characteristics are
electrons are in ________ defined by a probability.
each orbital at discrete __________ is determined by quantum numbers.  
Quantum # Designation
n = _________ (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 = ___________ 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
_________________________
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
_______ _______ 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 _______________.
• Large difference in _________________________.
• Example: NaCl
Na (metal)
unstable
Cl (nonmetal)
electron + -
Coulombic
Attraction
Na (cation)
stable
Cl (anion)

13. Ionic Bonding Energy – _________ energy most stable r A B
Energy balance of attractive and ________ 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 _________
NaCl
MgO
CaF 2
CsCl
Give up electrons
Acquire electrons

15. Covalent Bonding similar ______________ share electrons
bonds determined by ________ – s & p _________ dominate bonding
Example: H2 H2
Each H: has 1 valence e-,
needs 1 more H H
______________
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 _____ 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 ________
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 -- _________ as electron cloud
Ionic-Covalent Mixed Bonding
% ionic character =  
where XA & XB are _________ electronegativities %)
100 ( x
Ex: MgO XMg = XO = 3.5

19. Secondary Bonding + - Arises from interaction between _________
• Fluctuating _________
_________ 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 (__________)
Covalent
Variable
Directional
(_____________, ________
polymer chains)
large-Diamond
small-Bismuth
Metallic
Variable
large-Tungsten
Nondirectional (________)
small-Mercury
Secondary
smallest
Directional
inter-chain (_________)
inter-molecular

21. Properties From Bonding: Tm
• Bond length, r
• Melting Temperature, Tm r o
Energy r
• _______ energy, Eo Eo =
“bond energy”
Energy r o
unstretched length
________ Tm
larger Tm
___________ 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. _________ expansion Δ L = α ( T - T ) 2 1 L o
• α ~ symmetric at ro r o
smaller α
_______ α
Energy
___________ length Eo
________ if Eo is smaller.

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