Coordination number (CN): the number of nearest neighbor atoms/ions surrounding an atom/ion
Not stable
Stable
Determined by the ratio of radius of ions
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electron Nucleus
- Electrons are characterized by four quantum numbers
Principle quantum number: n = 1, 2, …. K, L, M, N, O,
Orbital quantum number: l = 0, 1, …, n-1 s, p, d, f
[2(C+A)]2 = (2A)2 + (2A)2 [(C+A)]2 = 2A2 (C+A)/A = 21/2 = 1.414 C/A = 0.414 The packing tends to have as more CN as possible
Example:
NaCl: R+ = 1.02; R- = 1.81; R+/R- = 1.02/1.81 = 0.564 CN = 6 MgO: R+ = 0.72; R- = 1.40; R+/R- = 0.72/1.40 = 0.514 CN = 6 SiO2: R+ = 0.40; R- = 1.40; R+/R- = 0.40/1.40 = 0.286 CN = 4
Electrons repulse each other – keep atoms in certain distance Electron and nuclei attract each other – bonding
Characters: Close-packed structures in pure metals Ductility High electric and thermal conductivity Shiny
Only those electrons which occupy the outermost shell will involve in chemical reaction; called valence electrons.
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1.2 Bonding - Metallic bonding The valence electrons are freely shared by all the atoms in the structure
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- Ionic and covalent bond combination
CaSO4
O (8): S (16): Ca (20):
1s22s22p4 1s22s22p63s23p4 1s22s22p63s23p64s2
Forming covalent bond between : S and O
Chapter 12 Optical properties
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Chapter 1: Atomic Bonding
1.1 Atomic structures
- Atom consists of a nucleuቤተ መጻሕፍቲ ባይዱ (positive charged) and electrons (negative charged)
Magnetic quantum number: m = l, .., 1, 0, -1, …-l Spin quantum number: s:1/2 and -1/2
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n: determines the position of the shell. l: determines the shape of orbitals or subshells in each shell. m: represents the orientation/number of the orbitals within each shell. s: represents the direction of spin.
Pauli exclusion principle: no electron can have the same set of four quantum numbers
l
m
number of orbitals
0, s
0
1
1,p
+1，0，-1
3
2,d
+2，+1，0，-1，-2
5
3,f +3，+2，+1, 0, -1, -2,-3
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- Ionic bonding Atom gives up one or more electrons – positive charge (Cation) Atom accepts one or more electrons – negative charge (Anion) Coulombic attraction force – source of ionic bonding E.g.: NaCl
Na(11):1s22s22p63s1 Cl(17): 1s22s22p63s23p5 For pure ionic bonding, it would be nondirectional
close-packed.
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The packing pattern of ionic bonding structures: determined by (i) electrical neutrality (ii) sizes of ions
Fundamental of Materials Science and Engineering
Introduction
Chapter 1 Atomic Bonding
References:
Chapter 2 Crystal Structures Chapter 3 Defects Chapter 4 Glass structure Chapter 5 Phase diagram
p s
sp1 hybrid orbital: one s orbital and one p orbitals are mixed together to form two new orbitals. The remaining two p orbitals are unaffected. Two sp1 orbitals are on the same line and form angle of 180o between them.
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Energy
Relative energy level of orbitals
6s 5p 4d 5s 4p 3d 4s 3p 3s 2p 2s 1s Each orbital consists of 2 electrons.
Electrons fill the orbitals with lowest energy first.
Directional Not close-packed
Hybridization
sp3 hybrid orbital: one s orbital and 3 p orbitals are mixed together to form four new orbitals. Each orbital points to one corner of tetrahedral and form angle of 109.5o between them.
7
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n
lm
10
0
# of orbital 1
Maximum #
of electrons
1s
2
20
0
1 1, 0, -1
1
2s 2 8
3
2p 6
0 31
0 1, 0, -1
1 3
3s 2 3p 6
18
2 2, 1, 0, -1, -2
5
3d 10
Electron # in each shell: 2n2
Forming ionic bond between SO4 and Ca
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- Van der Waals Bonding Weaker bond other than metallic, ionic and covalent bonds
Molecular polarization
HCl
+
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- Covalent bonding
•Two or more atoms share electrons such that each achieves a stable structure
•Unlike metallic and ionic bonding, covalent bonding is directional – due to shape of orbital
p s
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- Bonding strength/force
mn
• The first term is attractive, and the second is repulsive. • At r <ro, the equilibrium value, the repulsive force dominates and U rises. • The force F is given by the rate of change of energy with distance dU/dr and is zero at r =ro.
Materials Science and