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ATOMIC STRUCTURE(SUBJECT : INORGANIC CHEMISTRY)
SCIENCE EDUCATION MASTER DEGREE PROGRAM THE STATE UNIVERSITY OF SURABAYA
ULIVINA PRATINI(127795086)
Democritus, systematized his
views. In approximately 450 BC,
Democritus coined the term
átomos, which means
"uncuttable" or "the smallest
indivisible particle of matter".
1. History of The Atom
In 1805, English instructor and natural
philosopher John Dalton used the
concept of atoms.
He proposed that each element
consists of atoms of a single, unique
type, and that these atoms can join
together to form chemical compounds.
1. History of The Atom
• Experiments by J.J. Thomson in the 1890’s showed that atoms contain electrons.
• Cathode ray tube
1. History of The Atom
Electric Potential = Voltage
Ulivina Pratini (127795086)
13/04/2023
13/04/2023Ulivina Pratini (127795086)
• The Plum Pudding (Chocolate Chip Cookie) Model
1. History of The Atom
13/04/2023Ulivina Pratini (127795086)
• Rutherford’s Experiment (1911)
α particles are very small and positively charged
1. History of The Atom
13/04/2023Ulivina Pratini (127795086)
• Results of the Rutherford experiment
(a) The results that the metal foil experiment would have yielded if theplum pudding model had been correct
(b) Actual results
1. History of The Atom
1. Since most of the alpha particles were
passed through the foil undeflected,
therefore, it was concluded that most of
the atom is empty.
2. Small angles of deflection indicate that
positively charged alpha particles were
attracted by electrons.
3. Large angles of deflection indicate that
there is a massive positively charged
body present in the atom and due to
repulsion alpha particles were deflected at
large angles.
EXPLANATION OF POSTULATES
RUTHERFORD'S ATOMIC THEORY
13/04/2023Ulivina Pratini (127795086)
• Comparing the Parts of an Atom
2. COMPONENTS
There were two fundamental defects in Rutherford's atomic model: According to classical electromagnetic theory,
being a charge particle electron when accelerated must emit energy. We know that the motion of electron around the nucleus is an accelerated motion, therefore, it must radiate energy. But in actual practice this does not happen. Suppose if it happens then due to continuous loss of energy orbit of electron must decrease continuously. Consequently electron will fall into the nucleus. But this is against the actual situation and this shows that atom is unstable.
If the electrons emit energy continuously, they should form continuous spectrum. But actually line spectrum is obtained
DEFECT OF RUTHERFORD’S THEORY
13/04/2023Ulivina Pratini (127795086)
3. ATOMIC LINE SPECTRA
•Bohr’s greatest contribution to
science was in building a simple
model of the atom.
• It was based on understanding
the SHARP LINE SPECTRA of
excited atoms.Niels Bohr (1885-1962)
(Nobel Prize, 1922)
Line Spectra of Excited Atoms
3. ATOMIC LINE SPECTRA
• Excited atoms emit light of only certain wavelengths• The wavelengths of emitted light depend on the
element.
H
Hg
Ne
Ulivina Pratini (127795086) 13/04/2023
13/04/2023Ulivina Pratini (127795086)
+Electronorbit
2. But a charged particle moving in an electric field should emit energy.
1. Classically any orbit should be possible and so is any energy.
4. Atomic Spectra and Bohr Model
One view of atomic structure in early 20th century was that an electron (e-) traveled about the nucleus in an orbit.
13/04/2023Ulivina Pratini (127795086)
• Bohr said classical view is wrong. Need a new theory — now called QUANTUM or WAVE MECHANICS.
• e- can only exist in certain discrete orbit — called stationary states.
• e- is restricted to QUANTIZED energy states.
4. Atomic Spectra and Bohr Model
13/04/2023Ulivina Pratini (127795086)
4-H_SPECTRA.MOV
H atom
07m07an1.mov
If e-’s are in quantized energy states, then DE of states can have only certain values. This explains sharp line spectra.
4. Atomic Spectra and Bohr Model
n = 1
n = 2E = -R (1/22)
E = -R (1/12)
R, the Rydberg constant. R = 1312 kJ/mol or 3.29 x 1015 Hz
13/04/2023Ulivina Pratini (127795086)
Hydrogen atom spectra
Visible lines in H atom
spectrum are called the
BALMER series.
High EHigh EShort Short High High
Low ELow ELong Long Low Low
En
erg
y
Ultra VioletLyman
InfraredPaschen
VisibleBalmerEn = -1312
n2
65
3
2
1
4
n
13/04/2023Ulivina Pratini (127795086)
Each stationary orbit corresponds to a definite energy.There stationary orbit are designated by K,L,M,N,O,… .The orbit close to the nucleus has less energy compared to the orbit away from the nucleus.
4. Atomic Spectra and Bohr Model
13/04/2023Ulivina Pratini (127795086)
Atomic spectra display fine structure due to splitting of spectral lines. I an attempt to account for the fine structure, Arnold Sommerfeld proposed elliptical orbits instead of circular orbits proposed by Bohr.
=
13/04/2023Ulivina Pratini (127795086)
From Bohr model to Quantum mechanics
• Bohr’s theory was a great accomplishment
and radically changed our view of matter.
• But problems existed with Bohr theory —– theory only successful for the H atom.
– introduced quantum idea artificially.
• So, we go on to QUANTUM or WAVE
MECHANICS
13/04/2023Ulivina Pratini (127795086)
5. Quantum or Wave Mechanics
• Light has both wave & particle properties
• de Broglie (1924) proposed that all moving objects have wave properties.
• For light: E = hn = hc / l• For particles: E = mc2 (Einstein)L. de Broglie
(1892-1987)
l for particles is called the de Broglie wavelength
and for particles (mass)x(velocity) = h / l
Therefore, mc = h / l
13/04/2023Ulivina Pratini (127795086)
Uncertainty Principle
13/04/2023Ulivina Pratini (127795086)
W. Heisenberg1901-1976
Uncertainty Principle Problem of defining nature of
electrons in atoms solved by W.
Heisenberg.
Cannot simultaneously define the
position and momentum (= m•v) of an
electron.
Dx. Dp = h
At best we can describe the position
and velocity of an electron by a
PROBABILITY DISTRIBUTION,
which is given by Y2
13/04/2023Ulivina Pratini (127795086)
E. Schrodinger1887-1961
Schrodinger applied idea of e- behaving
as a wave to the problem of electrons in
atoms.
Solution to WAVE EQUATION gives set of
mathematical expressions called
WAVE FUNCTIONS, Y
Each describes an allowed energy state
of an e-
Quantization introduced naturally.
5. Quantum or Wave Mechanics
13/04/2023Ulivina Pratini (127795086)
WAVE FUNCTIONS, Y
• Y is a function of distance and two angles.
• For 1 electron, Y corresponds to an
ORBITAL — the region of space within which an electron is found.
• Y does NOT describe the exact location of the electron.
• Y2 is proportional to the probability of finding an e- at a given point.
13/04/2023Ulivina Pratini (127795086)
Y2 is proportional to the probability of finding an e- at a given point.
13/04/2023Ulivina Pratini (127795086)
7. Orbital Quantum Numbers
• An atomic orbital is defined by 3 quantum numbers:– n l ml
• Electrons are arranged in shells and
subshells of ORBITALS .• n shell
• l subshell
• ml designates an orbital within a subshell
13/04/2023Ulivina Pratini (127795086)
Quantum Numbers
mmll (magnetic)(magnetic) --l..0..+ll..0..+l Orbital orientationOrbital orientationin spacein space
l l (angular)(angular) 0, 1, 2, .. n0, 1, 2, .. n--11 Orbital shape orOrbital shape ortype type ((subshellsubshell))
n (major) 1, 2, 3, .. Orbital size andenergy = -R(1/n2)
Total # of orbitals in lth subshell = 2 l + 1
SymbolSymbol ValuesValues DescriptionDescription
13/04/2023Ulivina Pratini (127795086)
Shells and Subshells
For n = 1, l = 0 and ml = 0There is only one subshell and that subshell has a single orbital(ml has a single value ---> 1 orbital)
This subshell is labeled s (“ess”) and
we call this orbital 1sEach shell has 1 orbital labeled s. It is SPHERICAL in shape.
13/04/2023Ulivina Pratini (127795086)
s OrbitalsAll s orbitals are spherical in shape.
13/04/2023Ulivina Pratini (127795086)
When l = 1, there is a PLANAR NODE through the nucleus.
planar node
Typical p orbitalp OrbitalsFor n = 2, l = 0 and 1There are 2 types of orbitals — 2 subshells For l = 0 ml = 0 this is a s subshell For l = 1 ml = -1, 0, +1
this is a p subshell with 3 orbitals
13/04/2023Ulivina Pratini (127795086)
The three p orbitals lie 90o apart in space
pz
py
px90o
A p orbital
p orbitals (2)
13/04/2023Ulivina Pratini (127795086)
p-orbitals(3)
px py pz
2
3
n=
l =
13/04/2023Ulivina Pratini (127795086)
For l = 2, ml = -2, -1, 0, +1, +2
d subshell with 5 orbitals
For l = 1, ml = -1, 0, +1 p subshell with 3 orbitals
For l = 0, ml = 0
s subshell with single orbital
For n = 3, what are the values of l?l = 0, 1, 2
and so there are 3 subshells in the shell.
d Orbitals
13/04/2023Ulivina Pratini (127795086)
d Orbitals
IN GENERALthe number of NODES= value of angular quantum number (l)
s orbitals have no planar node (l = 0) and so are spherical.p orbitals have l = 1, and have 1 planar node,and so are “dumbbell” shaped.d orbitals (with l = 2) have 2 planar nodes
typical d orbital
planar node
planar node
13/04/2023Ulivina Pratini (127795086)
Boundary surfaces for all orbitals of the n = 1, n = 2 and n = 3 shells
2
1
3dn=
3
There aren2
orbitals in the nth SHELL
13/04/2023Ulivina Pratini (127795086)
THANKS FOR YOUR ATTENTION