On-line_L1_Materials_Science_Concepts1
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Materials Science Concepts
MATS-535 Electronics and Photonics Materials
Dr. Vladimir Gavrilenko
Norfolk State University
Scope
a – Atomic Structure and Atomic Number
b – Bonding and Type of Solids
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Atomic Structure of Materials
•Basic building blocks of matter
•Classic vs. quantum treatments
•Models of atoms
•Bohr model
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Bohr Atom
Stable orbit has radius
ro
v
ro
-e
The planetary model of the hydrogen atom in which the negatively
charged electron orbits the positively charged nucleus.
Shell Model.
Carbon Atom
L shell with
two subshells
Nucleus
1s
K
L
2s
2p
1s22s22p2 or [He]2s22p2
The shell model of the atom in which the electrons are confined to
live within certain shells and in subshells within shells.
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Ionization Energy and Electron Affinity
0
-5.1 eV
H+
Ionization Energy – Smallest energy
required to remove an electron from
neutral atom
Electron Affinity – Energy that is needed
(or released) when one adds an electron to a
neutral atom
Na IE
-
H
Cl
-12.98 eV
-13.6 eV
H
EA
-
Cl
EA(H-)=0.7541 eV required energy
EA (Cl )=-349. kJ/mol =-3.62 eV released energy
1Takahashi
et al Rev. Sci. Instr. 71, 1101 (2000)
1 eV = 96.4 kJ/mol
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Atomic Scale Units
Fundamental au:
me 9.110 31 kg
11
o
r0 5.29 10 m 0.529 A
e 1.6 10 19 C
h
1.054 10 34 J s
2
e2
Eh
27.2 eV
40 r0
C
1
40
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Atomic Mass and Mole
Atomic mass:
Avogadro’s number:
1
mC 1.66054 1027 kg
12
N A 6.022 1023
mat
One mole of a substance has a mass equal to its atomic (molecular) mass
in grams
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Atomic Bonding
ro
r=
Molecule
FR = Repulsive force
(a) Force vs r
Attraction
Potential Energy, E(r)
Attraction
FN = Net force
Interatomic separation, r
Repulsion
Force
FA = Attractive force
ro
0
+
Separated atoms
ER = Repulsive PE
E = Net PE
0
Repulsion
+
Eo
r
ro
EA = Attractive PE
(b) Potential energy vs r
(a) Force vs interatomic separation and (b) Potential energy vs
interatomic separation.
Atomic Bonding
Why the materials are stable?
What prevents from the collapse?
Equilibrium conditions:
Ftot FA FR 0,
dEtot
Ftot
0,
dr
min
Etot Etot
Bond energy is an energy that is required to separate to particles
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Covalent Bonding
H-atom
H-atom
Electron shell
1s
1s
Covalent bond
H-H Molecule
2 1
2
1
1
2
Formation of a covalent bond between two H atoms leads to the H2
molecule. Electrons spend majority of their time between the two
nuclei which results in a net attraction between the electrons and the
two nuclei which is the origin of the covalent bond .
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Methane Molecule
109.5°
Covalent bond
H
H
H
H
C
H
L shell
C
H
C
K shell
H
H
H
H
covalent
bonds
H
H
(a)
(c)
(b)
(a) Covalent bonding in methane, CH4, involves four hydrogen
atoms sharing electrons with one carbon atom. Each covalent bond
has two shared electrons. The four bonds are identical and repel
each other.
(b) Schematic sketch of CH4 on paper.
(c) In three dimensions, due to symmetry, the bonds are directed
towards the corners of a tetrahedron.
Diamond Crystal
The diamond crystal is a covalently bonded network of carbon atoms.
Each carbon atom is bonded covalently to four neighbors forming a
regular three dimensional pattern of atoms which constitutes the
diamond crystal.
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Metallic Bond
FCC Copper:
Positive metal
ion cores
Free valence
electrons forming an
electron gas
In metallic bonding the valence electrons from the metal atoms
form a "cloud of electrons" which fills the space between the
metal ions and "glues" the ions together through the coulombic
attraction between the electron gas and positive metal ions.
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Ionic Bond
Cl
Na
3s
3s 3p
Closed K and L shells
Closed K and L shells
(a)
Cl-
ClNa+
Na+
FA
FA
r
(b)
3s
3p
ro
(c)
The formation of an ionic bond between Na and Cl atoms in NaCl.
The attraction is due to coulombic forces.
Simple Cubic Structure
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+
Cl-
Cl-
Na+
Cl-
Na+
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Cl-
(a)
Cl-
Cl- Na+
ClNa+
(b)
(a) A schematic illustration of a cross section from solid NaCl.
NaCl solid is made of Cl- and Na+ ions arranged alternatingly so
that the oppositely charged ions are closest to each other and attract
each other. There are also repulsive forces between the like-ions. In
equilibrium the net force acting on any ion is zero.
(b) Solid NaCl.
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6
Cl
0
-6
-6.3
Cl
r=
+
Na
1.5 eV
0.28 nm
Cohesive energy
Potential energy E(r), eV/(ion-pair)
Potential Energy Plot
Cl
r=
Separation, r
Na
+
Na
ro = 0.28 nm
Sketch of the potential energy per ion-pair in solid NaCl. Zero
energy corresponds to neutral Na and Cl atoms infinitely separated.
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Primary and Secondary Bonds
H
Cl
B
A
Primary bonds:
-Metallic
-Ionic
-Covalent
Secondary bonds:
-Van der Waals type
-Hydrogen type
B
A
(a)
(b)
(c)
(a) A permanently polarized molecule is called a an electric dipole
moment.
(b) Dipoles can attract or repel each other depending on their relative
orientations.
(c) Suitably oriented dipoles attract each other to form van der Waals
bonds.
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Van der Waals Bonds
H
O
H
(a)
(b)
The origin of van der Waals bonding between water molecules.
(a) The H2O molecule is polar and has a net permanent dipole
moment.
(b) Attractions between the various dipole moments in water gives
rise to van der Waals bonding.
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Van der Waals Bonds
Time averaged electron (negative charge)
distribution
Closed L Shell
Ne
Instantaneous electron (negative charge)
distribution fluctuates about the nucleus.
Ionic core
(Nucleus + K-shell)
B
A
vanderWaals force
Synchronized fluctuations
of the electrons
Induced dipole-induced dipole interaction and the resulting van der
Waals force.
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