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

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• Rutherford’s Experiment (1911)

α particles are very small and positively charged

1. History of The Atom

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• 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

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• 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

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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

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+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.

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• 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

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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

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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

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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

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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.

=

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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

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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

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Uncertainty Principle

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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

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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

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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.

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Y2 is proportional to the probability of finding an e- at a given point.

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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

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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

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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.

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s OrbitalsAll s orbitals are spherical in shape.

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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

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The three p orbitals lie 90o apart in space

pz

py

px90o

A p orbital

p orbitals (2)

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p-orbitals(3)

px py pz

2

3

n=

l =

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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

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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

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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

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THANKS FOR YOUR ATTENTION