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Chapter 2 - 1
ISSUES TO ADDRESS...
• What promotes bonding?
• What types of bonds are there?
• What properties are inferred from bonding?
Chapter 2: Atomic Structure & Interatomic Bonding
Chapter 2 - 2
Atomic Structure (Freshman Chem.)• atom – electrons – 9.11 x 10-31 kg
protons neutrons
• atomic number = # of protons in nucleus of atom = # of electrons of neutral species
• A [=] atomic mass unit = amu = 1/12 mass of 12C Atomic wt = wt of 6.022 x 1023 molecules or atoms
1 amu/atom = 1g/mol
C 12.011H 1.008 etc.
} 1.67 x 10-27 kg
Chapter 2 - 3
number of neutrons = Nnumber of protons = Z
A= Z + N (2.1)
AVAGADRO’S NUMBER = 6.022 x 1023 = NA
ATOMIC OR MOLECULAR WEIGHT =
NA x WEIGHT PER ATOM.
Chapter 2 - 4
Atomic Structure
• Valence electrons determine all of the following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 2 -
BOHR ATOM
5
Chapter 2 -
WAVE MECHANICAL MODEL OF ATOM
6
Chapter 2 - 7
Electronic Structure
• Electrons have wavelike and particulate properties. – This means that 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
Chapter 2 - 8
Electron Energy States
1s
2s2p
K-shell n = 1
L-shell n = 2
3s3p M-shell n = 3
3d
4s
4p4d
Energy
N-shell n = 4
• have discrete energy states• tend to occupy lowest available energy state.
Electrons...
Adapted from Fig. 2.4, Callister & Rethwisch 8e.
Chapter 2 - 9
• Why? Valence (outer) shell usually not filled completely.
• Most elements: Electron configuration not stable.
SURVEY OF ELEMENTS
Electron configuration
(stable)
...
...
1s22s 22p 63s23p 6 (stable)... 1s22s 22p 63s23p 63d 10 4s 24p 6 (stable)
Atomic #
18...36
Element1s1 1Hydrogen1s22Helium1s22s 1 3Lithium1s22s24Beryllium1s22s 22p 15Boron1s22s 22p 26Carbon
...
1s22s 22p 6 (stable)10Neon1s22s 22p 63s111Sodium1s22s 22p 63s2 12Magnesium1s22s 22p 63s23p 113Aluminum
...
Argon...Krypton
Adapted from Table 2.2, Callister & Rethwisch 8e.
Chapter 2 - 10
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
Chapter 2 - 11
Electronic Configurationsex: Fe - atomic # = 26
valence electrons
Adapted from Fig. 2.4, Callister & Rethwisch 8e.
1s
2s2p
K-shell n = 1
L-shell n = 2
3s3p M-shell n = 3
3d
4s
4p4d
Energy
N-shell n = 4
1s2 2s2 2p6 3s2 3p6 3d 6 4s2
Chapter 2 - 12
The Periodic Table• Columns: Similar Valence Structure
Adapted from Fig. 2.6, Callister & Rethwisch 8e.
Electropositive elements:Readily give up electronsto become + ions.
Electronegative elements:Readily acquire electronsto become - ions.
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- ine
rt g
ase
s
acc
ept
1e
-
acc
ept
2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
ClS
Li Be
H
Na Mg
BaCs
RaFr
CaK Sc
SrRb Y
Chapter 2 - 13
• Ranges from 0.7 to 4.0,
Smaller electronegativity Larger electronegativity
• Large values: tendency to acquire electrons.
Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
Electronegativity
Chapter 2 - 14
Ionic bond – metal + nonmetal
donates accepts electrons electrons
Dissimilar electronegativities
ex: MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6 [Ne] [Ne]
Chapter 2 -
Electrons in different shells
15
Chapter 2 -
Electrons in Sodium and Chlorine
16
TABLE 2.2 / P 25 3s1
3s2 3p5
Chapter 2 - 17
• Occurs between + and - ions.
• Requires electron transfer.
• Large difference in electronegativity required.
• Example: NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 2 - 18
Chapter 2 -
FORCES AND ENERGIES
19
Chapter 2 - 20
Chapter 2 - 21
Chapter 2 -
Bonding Forces and Energies
22
2.13 Calculate the force of attraction between a K+ and an O2- ion the centers of which are separated by a distance of r0 =1.5 nm.
The attractive force between two ions FA is just the derivative with respect to the interatomic separation of the attractive energy expression, Equation 2.8, which is just
Solution
Chapter 2 - 23
FA = dEAdr
= d
A
r
dr =
A
r2
The constant A in this expression is defined in footnote 3. Since the valences of the K+ and O2- ions
(Z1 and Z2) are +1 and -2, respectively, Z1 = 1 and Z2 = 2, then
Chapter 2 - 24
FA = (Z1e) (Z2e)
40r2
= (1)(2)(1.602 10 19 C)2
(4)() (8.85 10 12 F/m) (1.5 10 9 m)2
=2.05 10^(-10 ) N
Chapter 2 -
IONIC FORCE / P 31 FOOT-NOTE
25
F= (Z1 *Z2 * e^2)/(4*π*ε0*r^2);
e= 1.602 *10^(-19) COULOMBS ;
ε0 = 8.85 * 10^(-12 )
Z1, Z2 = VALENCIES OF IONS
Chapter 2 - 26
Ionic Bonding
• Energy – minimum energy most stable– Energy balance of attractive and repulsive terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
rA
nrBEN = EA + ER =
Adapted from Fig. 2.8(b), Callister & Rethwisch 8e.
Chapter 2 - 27
• Predominant bonding in Ceramics
Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.
Examples: Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF2CsCl
Chapter 2 - 28
C: has 4 valence e-, needs 4 more
H: has 1 valence e-, needs 1 more
Electronegativities are comparable.
Adapted from Fig. 2.10, Callister & Rethwisch 8e.
Covalent Bonding• similar electronegativity share electrons• bonds determined by valence – s & p orbitals dominate bonding
• Example: CH4
shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 2 - 29
Primary Bonding• Metallic Bond -- delocalized as electron cloud
• Ionic-Covalent Mixed Bonding
% ionic character =
where XA & XB are Pauling electronegativities
%)100( x
1 e
(XA XB )2
4
ionic 73.4% (100%) x e1 characterionic % 4)2.15.3(
2
Ex: MgO XMg = 1.2XO = 3.5
Chapter 2 -
METALLIC BONDING
30
Chapter 2 - 31
Arises from interaction between dipoles
• Permanent dipoles-molecule induced
• Fluctuating dipoles
-general case:
-ex: liquid HCl
-ex: polymer
Adapted from Fig. 2.13, Callister & Rethwisch 8e.
Adapted from Fig. 2.15, Callister & Rethwisch 8e.
SECONDARY BONDING
asymmetric electron clouds
+ - + -secondary
bonding
HH HH
H2 H2
secondary bonding
ex: liquid H2
H Cl H Clsecondary bonding
secondary bonding+ - + -
secondary bondingsecondary bonding
Chapter 2 - 32
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large!
Variablelarge-Diamondsmall-Bismuth
Variablelarge-Tungstensmall-Mercury
smallest
Comments
Nondirectional (ceramics)
Directional(semiconductors, ceramicspolymer chains)
Nondirectional (metals)
Directionalinter-chain (polymer)inter-molecular
Summary: Bonding
Chapter 2 - 33
• Bond length, r
• Bond energy, Eo
• Melting Temperature, Tm
Tm is larger if Eo is larger.
Properties From Bonding: Tm
r o r
Energyr
larger Tm
smaller Tm
Eo =
“bond energy”
Energy
r o r
unstretched length
Chapter 2 - 34
• Coefficient of thermal expansion,
• ~ symmetric at ro
is larger if Eo is smaller.
Properties From Bonding :
= (T2 -T1)LLo
coeff. thermal expansion
L
length, Lo
unheated, T1
heated, T2
r or
smaller
larger
Energy
unstretched length
Eo
Eo
Chapter 2 - 35
Ceramics(Ionic & covalent bonding):
Large bond energylarge Tm
large Esmall
Metals(Metallic bonding):
Variable bond energymoderate Tm
moderate Emoderate
Summary: Primary Bonds
Polymers(Covalent & Secondary):
Directional PropertiesSecondary bonding dominates
small Tm
small E large
secondary bonding
Chapter 2 - 36
Reading:
Core Problems:
Self-help Problems:
ANNOUNCEMENTS
