Atomic Spectra and
Models of the Atom
• LEARNING OBJECTIVE
To know the relationship between atomic
spectra and the electronic structure of
atoms.
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
Atomic Spectra and
Models of the Atom
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
What do you know?
• What is an atom?
• What are atoms made of?
• How/when were the atom components
discovered?
• What size is an atom?
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
FIRST DISCOVERIES
• 1897 Joseph John Thomson (1856-1940)
discovered the electron, experimentally
determining its charge to mass ratio
e/m =1.7591011 C/kg and concluded that they
are a component of every atom.
• 1909 Robert Millikan (1868-1953) - Oil drop
experiment - determined the charge and the mass
of an electron.
e =1.602 10-19 C
m = 9.11 10-31 kg
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
HISTORY OF THE ATOM
TIMELINE
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
ATOMIC MODELS
Thomson (1902)
Rutherford (1911)
Bohr-Sommerfeld (1913)
Shrödinger (1926)
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
THOMSON’S MODEL
(1902)
Plum Pudding Model
Electrons are surrounded by a
soup of positive charge to
balance the electrons negative
charges,
like negatively charged "plums"
surrounded by positively
charged "pudding"
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
The Gold Foil Experiment
Rutherford, Geiger & Marsden (1911):
The Gold Foil Experiment
“ It was almost as incredible as if you fired
a 15-inch shell at a piece of tissue paper
and it came back and hit you.”
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
The Gold Foil Experiment
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
RUTHERFORD MODEL
(1911)
An atom contains a
small dense positive
charge surrounded by
negatively charged
electrons revolving
around the positive
charge just like planets
orbit the sun.
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
But…
An accelerating charged particle emits
electromagnetic radiation
The orbiting electron has centripetal acceleration
It looses energy
The orbit radius decreases
The electron falls onto the nucleus in about 10-11s
The atom is not stable
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
What do you know so far?
• Who discovered the electron?
• What is the plum-pudding model?
• Why was the Rutherford’s “gold foil”
experiment outcome surprising?
• What is new in Rutherford’s model?
• Why wasn’t it a suitable model?
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
FROM CLASSICAL TO
QUANTUM PHYSICS
When you try to apply the classical mechanics
(Newton’s) laws to microscopic objects –
such as atoms and the e.m. waves they emit –
you come to contradictions with experience.
Therefore the fundamental dynamics’ and
electromagnetism’ laws have to be changed
so that the new laws correctly describe
microscopic phenomena, but reduce to
classical laws when applied to macroscopic
objects.
“Correspondence Principle” – Niels Bohr
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
BOHR MODEL
The electrons move about
the nucleus in "stationary
states" which are stable,
NOT radiating energy.
Each orbit can hold no
more than 2 electrons.
(Pauli’s Exclusion
Principle, 1925)
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
ELECTRONIC
TRANSITIONS
An electron is able to
absorb or emit energy
in order to “jump” from one to the other
orbit.
But what is it exchanging energy with?
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
The photon
Some metals emit electrons
when light shines on them:
the brighter the light,
the more electrons.
Einstein (1905) explained the
effect by describing light as
a bundle of particles, or
photons.
A photon gives a quantum of
energy depending on its
frequency E = hf = hc/.
h  6.63  10 34 Js
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
COMPTON EFFECT
(1923)
If a photon has high energy (X-rays), the electron is being
given enough energy to be completely ejected from its
atom, and a photon containing the remaining energy being
scattered in a different direction from the original.
LIGHT = PARTICLE (PHOTON)
ABSORPTION
An atom can absorb a photon
of light, so that an electron
“jumps” to an orbit that has a
higher energy.
This can only happen if the
photon energy equals the
difference in energy between
the two states
DE = h f
h  6.63  10 34 Js
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologicoprof.ssa
Didattico
CLILAprile
2013
Daniela
Modulo CHIMICA
Ist.Istr. Sup. “G. Verga” Modica
EMISSION
When an atom in an excited
state undergoes a transition
to the ground state, it loses
energy by emitting a
photon whose energy
corresponds to the
difference in energy
between the two states
DE = h f
h  6.63  10 34 Js
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
What do you know so far?
• What is new in Bohr’s model?
• What is the light made of?
• How can an atom absorb/emit energy?
• How much energy can the atom
absorb/emit?
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
GAS SPECTRA
Each element has characteristic emission and
absorption spectra, so scientists can use
such spectra to analyze the composition of
matter.
ACTIVITY
• Play the game!
http://spiff.rit.edu/classes/phys301/lectures/sp
ec_lines/Atoms_Nav.swf
• Read “how to”
• Do the exercises
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA
SPECRTOSCOPY
Spectra are used to provide information about the composition of a
substance or an object.
In particular, astronomers use emission and absorption spectra to
determine the composition of stars and interstellar matter.
We now know that the sun contains large amounts of hydrogen,
iron, and carbon, along with smaller amounts of other elements.
D.Aprile, C.Schipilliti, A.Consolo, M.D.Pappalardo
Corso di Perfezionamento Metodologico Didattico CLIL 2013
Modulo CHIMICA