1. CHAPTER 2: BONDING AND PROPERTIES
Properties depend on
- arrangement of atoms
- interactions between atoms
Study Bonding:
• 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
nucleus of atom: “size of a point on a page” -! فراغ
atomic number = No. of protons in nucleus of atom = No. of electrons of neutral species
 A [=] atomic mass unit = amu = 1/12 mass of 12C   Atomic wt = wt of x 1023 molecules or atoms   Unit 1 amu/atom = 1g/mol
C H etc.
} 1.67 x kg

3. Atomic Structure Valence electrons: in the outer-shell
determine all of the following properties
Chemical: reactivity
Electrical: conductivity
Thermal: conductivity
Optical: transmittance

4. Electronic Structure - Review
Electrons have wavelike and particulate properties.
This means that electrons are in orbitals defined by a probability.
Each orbital at discrete energy level 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 (direction in space) 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

6. SURVEY OF ELEMENTS - Review
• Most elements: Electron configuration not stable.
Electron configuration
(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
• 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
Primary Bonding: Ionic, Covalent and Metallic
example: C (atomic number = 6)
1s2 2s2 2p2
valence electrons

8. Electronic Configurations
ex: Fe - atomic # = 26
1s2 2s2 2p6 3s2 3p6
3d 6 4s2
valence
electrons 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

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
Electropositive elements:
Readily give up electrons
to become + ions.
Electronegative elements:
Readily acquire electrons
to become - ions.

10. Electronegativity • Ranges from 0.7 to 4.0,
• 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  1s 2 2s 2p 6
(stable) 10
Neon
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. Examples: Ionic Bonding
• Predominant bonding in Ceramics
NaCl
MgO
Give up electrons
Acquire electrons
CaF 2
CsCl

14. Covalent Bonding similar electronegativity  share electrons
bonds determined by valence – s & p orbitals dominate bonding
Example: CH4
shared electrons
from carbon atom
from hydrogen
atoms H C CH 4
C: has 4 valence e -,
needs 4 more
H: has 1 valence e -,
needs 1 more
Electronegativities
are comparable.

15. 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

16. SECONDARY BONDING + - Arises from interaction between dipoles
• Fluctuating dipoles
asymmetric electron
clouds + -
secondary
bonding H 2
ex: liquid H
• Permanent dipoles-molecule induced + -
-general case:
secondary
bonding
Adapted from Fig. 2.14,
Callister 7e. Cl Cl
-ex: liquid HCl
secondary H H
bonding
secondary bonding
-ex: polymer
secondary bonding

17. 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

18. Interactions Between Atoms
Far Atoms: Attraction
Close Atoms: Repulsion + -
Spacing (r)
Atomic Radius (R) + - + - r
Dynamic Equilibrium + -
Equilibrium spacing = ro
ro = 2 R

20. Bonding Curve

21. Bonding Curve 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 = - ro
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r

22. Bonding - Estimations r A B E = certain f(r) e.g. E = Eo =
Estimation of Bonding Energy (Eo) and Equilibrium Spacing (ro)
Given:
Bonding occurs at energy minimum
At minimum: Derivative dE/dr = g(r) = 0
Solve g(r) = 0 for r ro
Substitute r=ro in the Energy Eqn:
Get Eo = E (r=ro)
Atomic radius R = ro/2 r A n B
E = certain f(r) e.g. E = - Eo =
“bond energy”
Energy r o
For many atoms, ro is approximately 0.3 nm.

23. 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.

24. Properties From Bonding : a
• Coefficient of thermal expansion, a D L
length, o
unheated, T 1
heated, T 2
Coefficient of thermal expansion D L = a ( T - T ) 2 1 L o
• a ~ symmetry at ro r o
Smaller a
Larger a
Energy
unstretched length Eo
a is larger if Eo is smaller.

25. Summary: Primary Bonds
Ceramics
Large bond energy
large Tm
large E
small a
(Ionic & covalent bonding):
Metals
Variable bond energy
moderate Tm
moderate E
moderate a
(Metallic bonding):
Polymers
Directional Properties
Secondary bonding dominates
small Tm
small E
large a
(Covalent & Secondary):
secondary bonding
Bonding in Solids > Liquids > Gases

26. ANNOUNCEMENTS Reading: Focus on Atomic Bonding in Solids
Core Problems:
2.7, 2.8, 2.12, 2.13,
2.17, 2.19, 2.21 (Callister 3rd Addition)
Quiz: Next Class

27. Quiz Rank materials A, B and C according to
Increasing melting temperature > >
Decreasing bonding energy > >
Increasing Atomic Radius > >
Increasing coefficient of thermal expansion > >
Energy
Atomic Spacing r A B c

28. Quiz Rank materials A, B and C according to
Increasing melting temperature > >
Decreasing bonding energy > >
Increasing Atomic Radius > >
Increasing coefficient of thermal expansion > >
Energy A
Atomic Spacing r B c