atomic structure and interatomic bondingamoukasi/cbe30361/lecture_3_2014_lecture.pdf · electron...
TRANSCRIPT
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ATOMIC STRUCTURE AND
INTERATOMIC BONDING
Chapter 2
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Chapter 2: Main Concepts
1. History of atomic models: from ancient Greece to Quantum mechanics
2. Quantum numbers
3. Electron configurations of elements
4. The Periodic Table
5. Bonding Force and Energies
6. Electron structure and types of atomic bonds
7. Additional: How to see atoms: Transmission Electron Microscopy
Topics 1, 2 and partially 3: Lecture 3
Topic 5: Lecture 4
Topic 7: Lecture 5
Topics 4&6: self-education (book and/or WileyPlus)
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Question 1: What are the different levels of
Material Structure?
• Atomic structure (~1Angstrem=10-10 m)
• Crystalline structure (short and long-range
atomic arrangements; 1-10Angstroms)
• Nanostructure (1-100nm)
• Microstructure (0.1 -1000 mm)
• Macrostructure (>1000 mm)
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Q2: How does atomic structure influence the
Materials Properties?
• In general atomic structure defines
the type of bonding between elements
• In turn the bonding type (ionic, metallic,
covalent, van der Waals) influences the
variety of materials properties (module
of elasticity, electro and thermal
conductivity and etc.).
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MATERIALS CLASSIFICATION
• For example, five groups of
materials can be outlined based
on structures and properties:
- metals and alloys
- ceramics and glasses
- polymers (plastics)
- semiconductors
- composites
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Historical Overview
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A-tomos
Democritus
460-~370 BC
On philosophical
grounds:
There must be a
smallest indivisible
particle.
Arrangement of different
particles at micro-scale
determine properties at
macro-scale.
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Aristoteles 384-322 BC
fire
water
earth air
hot dry
wet cold
The four elements
from ancient times
It started
with …
Founder of Logic and
Methodology as tools for
Science and Philosophy Science?
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Newton ! (1643-1727)
Newton published in 1687:
‘Philosphiae Naturalis
Principia Mathematica’,
Origin of classical
mechanics
Gravitational force
Movement of the
planets
Newton
(by Godfrey Kneller, 1689)
… while the alchemists were
still in the ‘dark ages’.
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1814 1818 1826 Modern
O 16 16 16 16
S 32.16 32.19 32.19 32.07
P 26.80 31.88x2 31.38x2 30.98
*M 22.33 22.82 -- --
Cl -- -- 35.41 35.46
C 11.99 12.05 12.23 12.01
H 1.062 0.995 0.998 1.008
*M = ‘Murium’, an unknown element that, together with oxygen, forms ‘HCl’
(muriatic acid, ‘HMO’).
Berzelius! Atomic weights:
more clarity with the
help of physics.
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1817: Johann Dobereiner
(and others) noticed
relations between atomic
weights of similar elements:
Mg = 12
Ca = 12 + 8 =20
Sr = 20 + 24 = 44
Ba = 44 + 24 = 68
Dumas (1851):
N = 14
P = 14+ 17 = 31
As = 14 + 17 + 44 =75
Sb = 14 + 17 + 88 = 119
Bi = 14 + 17 + 176 = 207
Li = 7
Na = 7 + 16 = 23
K = 23 + 16 = 39
Also ‘lateral relations’ were
observed:
Cl - P = Br - As = I - Sb = 5
This led eventually to …
Triades !!! Regularities in atomic weights
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Mendeleev and simultaneously
Meyers: ordering according to atomic
weights and similar properties.
Start of the modern
Periodic Table
Based on his system Mendeleev
did correct predictions of still
unknown, missing elements.
Mendeleèff
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The original Atomic weights, not atomic numbers!
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“Modern History“
Erwin Schrödinger
1887-1961 Niles Bohr
1885-1962
(1) The grain-like “indivisible”
spices of Greek philosopher
Democritus
(2) The Rutherford-Chadwick
Model of the Atom
(3) Bohr’s model of electron
orbiting the nucleus
(4) Schrödinger's quantum
mechanical model of atom
Ernest Rutherford
1871-1937
Sir James Chadwick
1891-1974
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• Atoms = nucleus (protons and neutrons) + electrons
• Protons and neutrons have almost the same mass, 1.67 × 10-27 kg.
• Mass of an electron is much smaller, 9.11 × 10-31 kg
• Protons and electrons positive and negative charges of the same
magnitude, 1.6 × 10-19 Coulombs, while neutrons are electrically neutral.
The nucleus:
positively charged protons
and neutral particles-neutrons
Orbiting
electrons
The Rutherford-Chadwick
Planetary Model of the Atom
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Model Summary
• Atom, which means “indivisible” in Greek, has an internal structure !!
Atom=nucleus [protons (p) and neutrons (n)] + electrons (e)
• me= (9.109965 0.000014) x 10-31 kg
• mp= (1.67482 0.00008) x 10-27 kg
• mn= (1.67252 0.00008) x 10-27 kg
The atomic mass (A) ≈ mp + mn
• Ze=Zp = (1.60210 0.000013) x 10-19 Coulombs
• Zn=0
The atomic number (Z) = Number of protons (or electrons) in the atom
The atom isotope number is defined by Number of neutrons
mp ≈ mn >> me
Atom is neutral
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Obstacle #1
Rayleigh –Jeans
formula:
F(w, T)=w2kT/4p2c2
w
U(T) = w2kT/4p2c2 =
ultra-violet catastrophe !!
The thermal motion of electrons and the
thermal motion of ions relative to each
other lead (due to Maxwell equations), to
electromagnetic radiation as mentioned
above. This is called thermal radiation.
Physicist tried to understand how the
intensity of thermal radiation depends on
frequency. Experimentally obtained
results seemed to refuse to fit the
calculations. The theory predicted higher
contribution from higher frequencies but
the reality was that the intensity dropped
drastically at higher frequencies.
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Obstacle #2 The most serious obstacles with the planetary model is that an orbiting electron has a centripetal acceleration and, according to Maxwell's theory of electromagnetism, ought to lose energy by emitting electromagnetic radiation at a frequency equal to that of the orbital motion.
The radiated energy would be at the expense of the electrostatic potential energy of the electron, thus the electron approaches closer to the nucleus and experiences an increased electrostatic force.
It leads to increase of angular velocity of the orbiting electron; the frequency of the emitted radiation would also increase and the electron would spiral into the nucleus.
Calculations showed that collision between
electron and nucleus should happen
in a small fraction of a second,
thus atom should not be stable !!
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Quantum Mechanical
Model
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Time
Time
Wave-packet
Low frequency quanta
with law energy
High frequency quanta
with high energy
Am
plitu
de
A
mp
litud
e
Light comes only in packets
or quanta,
which energy proportional
to their frequency, n
or angular frequency w.
E = h∙n= w∙
where h = 6.6261937 10-37 J s
is Plank’s constant
Max Plank’s Idea
1)kT/exp(
1
c4T) f(w,
22
3
=
wp
w
Plank’s Formula
= h/2p - reduced Plank constant
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Bohr’s Postulates (1913)
The planetary model is correct, however, when an electron
is in an "allowed" orbit it does not radiate.
Conditions for “allowed” stationary orbit are:
L=me∙v∙r =n· where n=1,2,3…,
When electron “jumps” from one stationary orbit (m with energy Em) to
another (n and En) the radiation is absorbed (Em>En) or emitted (Em<En) in
the form of a single quantum (photon) of electromagnetic energy:
En-Em = ·w
Niles Bohr
1885-1962
i.e. electron angular moment is equal number of Plank’s constant
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Hydrogen Atom
Bohr’s model was able to
explain the stability of atoms as
well as the emission spectrum
of hydrogen.
Unfortunately, Bohr's model worked
only for hydrogen. Thus final atomic
model was yet to be developed.
mrn
nnZem
r
nvrm
r
Ze
r
vm
Bohr
e
n
e
e
10
2
2
2
0
2
0
2
10529.01
..)3,2,1(4
4
1
==
==
=
=
p
p
constRydberg
sZem
R
nmR
nm
Zem
EE
nn
ZemE
r
ZeE
r
ZevmE
e
e
mn
en
e
==
==
=
==
=
=
11616
2
42
0
22222
42
0
22
42
0
2
0
2
0
2
)100670687.2(1007.22
)4
1(
)11
()11
(2
)4
1(
,..)3,2,1(1
2)
4
1(
24
1
4
1
2
p
pw
w
p
p
p
rBohr - Bohr radius orbital electrons: n = principal quantum number
n=3 2 1
nucleus
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Hypothesis of Prince Louis de Broglie
In 1924 Louis de Broglie proposed that electrons
have a wave nature. He also described the relationship
between the wavelength of the wave and the mass and
speed of the particle:
1892-1987
Nobel prize 1929
The proposal has been experimentally (1927) confirmed and
is one of the fundamental aspects of Quantum Mechanics.
Photon energy: E=hw/2p
Photon impulse: p=h/l
Eq. of real plane wave:
x= A∙cos(wt-2px/l)
Electron wave frequency: w=2pE/h
Electron wave length: l=h/p
De Broglie wave function for free particle:
Y=A∙exp[(i2p/h)(p∙x-E∙t)]
2pw= n
n=c/l
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Schrödinger Equation (1926)
Erwin Schrödinger
1887-1961
Y=Aexp [i2p/h∙(p∙x-E∙t)]
Famous Schrödinger Equation
De Broglie Wave-function As it was explained by Max Born
dP = |Y|2dV is a probability that
particle could be detected inside
volume dV.
Energy
conservation
Law
U-is a potential
Energy
∫|Y|2dV=1 – standard
conditions
Y
=
YY=
Y 2
2
2
2
; pi
xE
i
t
2
222 1
;1
xp
tiE
Y
Y=
Y
Y=
;2
2
Um
pE =
tiU
xm
Y=Y
Y
2
22
2
tiU
m
Y=Y
2
2
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Schrödinger Atom Model
;0)4
1(
2
4
1
;0)(2
2
])/(exp[),,(),,,(
;0
2
0
2
2
0
2
2
=
=
=
=
=Y
=
p
p
r
ZeE
m
r
ZeUif
UEm
EUm
tEizyxtzyx
fieldstationaryt
Uif
The solution of the Schrödinger Equation for the
hydrogen atom is a formidable mathematical problem,
but is of high fundamental importance. The solution
is managed by separating variables so that the wave-
function is represented as follows:
The separation leads to three equations for the
three spatial variables, and their solutions give
rise to three quantum numbers associated with
the hydrogen energy levels.
or in polar coordinates
radial
colatitude
azimuthal equations
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• The principal quantum number n arises from the solution of the radial part of the
Schrödinger equation and describes the principle energy level of the electron.
• n is an integer that can range from 1 to infinity, with larger n corresponding
to higher energy orbital
• The bound state energies of the electron in the hydrogen atom are given by:
In the notation (e.g. of the periodic table), the main shells of electrons
are labeled K(n=1), L(n=2), M(n=3), etc. based on the principal quantum number.
The Principal Quantum Number
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The Orbital Quantum Number
From constrains on the behavior of the wave-function in the
colatitude equation arises a constant of the form:
where n is the principal quantum number
This defines the orbital quantum number, l, which determines the magnitude of the
orbital angular momentum, L, in the relationship:
The orbital quantum number, l, is
used as a part of the designation
of atomic electron states in the
spectroscopic notation
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The Magnetic Quantum Number
• While the above azimuthal dependence of the wave-function only requires the quantum number to be an integer, the coupling with the colatitude equation further constrains that its absolute value to be less than or equal to the orbital quantum number, l. The direct implication of this quantum number is the z-component of angular moment, Lz, is quantized according to:
• From the azimuthal equation comes a third quantum number, ml , with
the constraint:
ml is called the magnetic quantum number because the application of an external
magnetic field causes a splitting of spectral lines called the Zeeman effect.
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Summary of Schrödinger Model
• The electron energy, En, is defined by principle quantum number, n.
• For each value of En (except E1) one can find several wave-functions Ynlm, with different values of
l and ml quantum numbers.
• For each n, number of states with different l and ml equals:
21
0)12(
==
n
lnl
En
Ynlm
Quantum numbers
En
Ynlm
Quantum numbers
n
l
ml
n
l
ml
E1
Y100
1
0
0
E3
Y300
Y31-1
Y310
Y311
Y32-2
Y32-1
Y320
Y321
Yn322
3
3
3
3
3
3
3
3
3
0
1
1
1
2
2
2
2
2
0
-1
0
+1
-2
-1
0
+1
+2
E2
Y200
Y21-1
Y210
Y21+1
2
2
2
2
0
1
1
1
0
-1
0
+1
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Spin Quantum Number (I)
Spin, is a particle property, which tells us what the particle looks like from the
different directions. A particle with spin quantum number ms=0 , is like a dot
– looks same with different directions. A particle with ms =1 looks the same after
rotation a complete revolution. A particle with ms=2 looks the same after one turns
it round half evolution. The particles exist which you have to turn two complete
evolutions, ms =1/2 to look the same!!!
All the known particles in the Universe can be divided into two groups:
• Particles with ms =1/2 make the matter in the Universe, e.g. e, p, n and etc.
• Particles with ms = 0, 1, 2, give rise to force between the matter particles!!!
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Spin Quantum Number (II)
• A proper understanding of electron and other spin ½ particles came
1928 from theory proposed by Paul Dirac, who for the first time
combined both quantum mechanics and special theory of relativity.
Thus spin is quantum – relativistic property of the particles.
• This theory also predicted that electron should have a partner: anti-
electron or positron, which were discovered in 1932!!
2/1 ==sssz
mmM
Thus an electron may have spin equals +1/2 or –1/2 and number of the
electrons in atom with energy equals En may be not more than 2n2.
Paul Dirac
1902-1984
Nobel Prize 1933
Similarly to angular moment, spin projection on the z – direction
is also quantized according to:
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Pauli’s Exclusion Principle
All particles with ½ spin, i.e. the matter particles,
obey what is called Pauli’s exclusion principle:
Two similar particles cannot exist in the same state,
i.e. only one electron in atom can have a given
set of the four quantum numbers
Principle n = 1,2,3,…
Orbital l = 0,1,2, …n-1
Magnetic ml = 0, ±1,…, ± l
Spin ms = ±1/2
Wolfgang Pauli
1900-1958
Nobel Prize 1945
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The number of Electrons
in some Atom Shells
Number of Electrons Principle
Quantum
Number, n
Shell
Designation Subshells
Number of
states Per Sub-
shell
Per Shell
1
2
3
4
K
L
M
N
s
s
p
s
p
d
s
p
d
f
1
1
3
1
3
5
1
3
5
7
2
2
6
2
6
10
2
6
10
14
2
8
18
32
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• tend to occupy lowest available energy state or in other words, they fill quantum
levels in order of increasing energy.
• electrons that occupy the outermost filled shell – the valence electrons-
they are responsible for bonding and thus material properties!!!
Electrons...
ELECTRON ENERGY STATES
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• have complete s and p sub-shells, i.e. to have 8 valence electrons –
- the octet rule !!
• this tends the atom to be un-reactive (stable) like an inert gasses.
Stable electron configurations...
STABLE ELECTRON CONFIGURATIONS
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SURVEY of ELEMENTS K L M N
Element 1s 2s 2p 3s 3p 3d 4s 4p
1H
2He
1
2
-
-
-
-
-
-
-
-
-
-
-
-
-
-
3Li
4Be
5B
6C
7N
8O
9F
10N
2
2
2
2
2
2
2
2
1
2
2
2
2
2
2
2
-
-
1
2
3
4
5
6
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
11Na
12Mg
13Al
14Si
15P
16S
17Cl
18Ar
2
2
2
2
2
2
2
2
8
8
8
8
8
8
8
8
1
2
2
2
2
2
2
2
-
-
1
2
3
4
5
6
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
19K
20Ca
21Sc
22Ti
23V
24Cr
25Mn
26Fe
27Co
28Ni
2
2
2
2
2
2
2
2
2
2
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
-
-
1
2
3
5
5
6
7
8
1
2
2
2
2
1
2
2
2
2
-
-
-
-
-
-
-
-
-
-
29Cu
30Zn
31Ga
32Ge
33As
34Se
35Br
36Kr
2
2
2
2
2
2
2
2
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
10
10
10
10
10
10
10
10
1
2
2
2
2
2
2
2
-
-
1
2
3
4
5
6
Let us make columns of elements
with similar valence structure
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Periodic Table
• Elemental group indicates number of electrons available for bonding
For example: IA – Alkali metals (Li, Na, K..) – one electron in outermost occupied
s subshell, eager to give up electron-very active with low melting points;
VIIA –Halogens (F, Br, Cl…) – five electrons in outermost occupied p subshell,
need an electron to reach stable state – chemically active elements
0 - Inert gasses (he, Ne, Ar…) – have filled shells: chemically inactive
Dmitri Ivanovich Mendeleev
(1834-1907)
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Conclusions 1. Now you know physical interpretation of the quantum numbers and that they are
naturally coming from the solution of the wave equation:
The principal quantum number, symbolized as n can only have positive integer values (n=1,2,..)
As n increases, the electron is at a higher potential energy and is therefore less tightly bound to the nucleus. This is
the only quantum number introduced by the Bohr model.
The azimuthal quantum number, symbolized l, is a quantum number for an atomic orbital that determines its
orbital angular moment and describes the shape of the orbital (l=0,1,2..n-1).
The magnetic quantum number is the third of a set of quantum numbers is designated by the letter m, and refers,
loosely, to the direction of the angular momentum vector. The magnetic quantum number m only affects the
electron's energy if it is in a magnetic field because in the absence of one, all spherical harmonics corresponding to
the different arbitrary values of m are equivalent (m=-l, -l+1..0,1, ..+l ).
The spin quantum is designated by the letter s. Naturally comes from the relativistic wave equation and correctly
predicted the magnetic moment of electron, and at the same time treated the electron as a point particle (s = 0,1, ±1/2).
2.This numbers completely define the electron structures of the elements and allow to
predict type of bonds which one can expect during the interaction between these elements.
3. We know that the type of the atomic bonding defines materials properties.