Advanced Higher Chemistry

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Advanced Higher Chemistry
Unit 1 Electronic Structure and the Periodic Table
Topic 1 Electronic structure
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This unit covers
Topic 1 Electronic Structure 1.1 Electromagnetic
spectrum and associated calculations Schola
r topic 1 1.2 Electronic configuration and the
periodic table Scholar topic 2 1.3
Spectroscopy
Topic 2 Chemical Bonding 2.1 Covalent
bonding Scholar topic 3 2.2 Shapes of
molecules and polyatomic ions Scholar topic
4 2.3 Ionic lattices, superconductors and
semiconductors
Topic 3 Some Chemistry of the Periodic Table 3.1
2nd and 3rd short periods- oxides, chlorides and
hydrides Scholar topic 5 3.2 Electronic
configuration and the oxidation states of
transition metals 3.3 Transition metal
complexes Scholar topic 6
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What are atoms?
Aristotle, born 384- 322BC, tutored by Plato at
his Academy in Athens. He researched

• Astronomy
• Comets
• Geography
• rivers and physical features

• Chemistry
• Processes inc. burning
• Meterology
• Matter

• Physics
• Change
• Movement
• Space
• Position
• Time

• Mathematics
• important role in development of maths

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Historical perspectives
Ideas about elements http//www.chemsoc.org/timel
ine/pages/0400.html
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What is light?
1678 Christian Huygens (Nel) Proposed wave theory
of light
1752 Thomas Melvill (Sco) Put different
substances in flames, passed light through prism,
gave differently patterned spectra (Glasgow Uni)
1729 Pierre Bougeur (Fra) Light passing through a
liquid sample decreases as thickness increases
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1786 David Rittenhouse (USA) Makes 1st
diffraction grating with parallel hairs across 2
screws
1802 William Wollaston (Eng) Observes many thin
dark lines in the rainbow of colours in the
spectrum of the sun
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1814 Joseph von Frauenhofer (Ger) Invents
transmission diffraction grating and studies
detail of dark lines in solar spectrum
1820s William Herschel (Eng) Detected
identified small quantities of an element in a
powder put into a flame
1826 William Henry Fox Talbot (Sco) Observes
different salts produce colours when places in a
flame. Father of photography
1852 August Beer (Ger) Light absorbed was
proportional to the amount of solute in aqueous
solutions
1851 MA Masson 1st spark-emission spectroscope
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Uses?
1861 Thallium discovered
1861 James Clerk Maxwell (Sco) Model of light
being made up of electromagnetic radiation
1863 Indium discovered
1868 Helium discovered in the sun
1868 Anders Jonas Ångström (Swe) Publishes a
detailed study of the wavelengths of solar
spectral lines, expressed in units of 1010
meters, now known as the angstrom (Å). One of the
fathers of modern spectroscopy.
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Electromagnetic Spectrum- light
1. What is the electromagnetic spectrum?
All the different wavelengths of electromagnetic
radiation, including light, radio waves, and
X-rays. It is a continuum of wavelengths from
zero to infinity with different energies, and
arbitarily divided into different named regions
2. What is a light wave?
A form of emr which can be considered as a wave
and as particle
3. Which equation links frequency and wavelength?
Velocity (ms-1) wavelength (m) x frequency
(s-1) c ? x ? And wavenumber (often cm-1) ?
1 / ? (instead of frequency, m)
4. Link between frequency, wavelength and energy?
For a photon E h ?. For 1 mole of photons, E
L h c / ? or E L h ?
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Twinkle, twinkle little star
July 1054 Chinese astronomers and members of the
Anasazi tribe (native Americans living in
Arizona) saw a new star, even visible during
daytime
1800s Charles Messier saw fuzzy ball of light
like a comet, but not moving. Named M1
1960s One of first sources of X-rays detected
(Tau X-1)
What happened? Core of star collapsed, formed a
neutron star (pulsar). Released enough energy to
blast surface layers of star into space. Expelled
gases formed Crab Nebula...
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launched 1990
http//hubblesite.org/

• Observes at
• Visible
• Near-ultraviolet
• Near-infrared wavelengths
• (range 115 nm to 2115 nm)

Why?

• To investigate celestial bodies by studying
  their composition, physical characteristics, and
  dynamics (velocity)
• To observe the formation of stars and galaxies,
  and study their formation and evolution
• Studying the history and evolution of the
  universe

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Radio wavelengths Generated by unbound electrons
spiralling inside the nebula. Most intense (red)
to least (blue). Central pulsar emits at about 60
times a second (bright white spot)
Visible spectrum Blue core from electrons in
nebula being deflected and accelerated by
magnetic field of the central neutron star. Red
colour from emission of hydrogen as filaments
continue to travel out from central star.
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Ultraviolet wavelengths Cooler electrons emit uv
radiation and extend out beyond the hot electrons
near the central pulsar (which energises the
electrons)
X-rays Condensed core pulses X-rays (radio
optical) How? Strong magnetic field heats up
electrons near the pulsar surface which then
release X-rays
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Multiwavelength astronomy
http//imagine.gsfc.nasa.gov/docs/science/know_l2/
multiwavelength.html
Look at the tour of the Crab nebula
at http//hubblesite.org/gallery/album/tours/tour
-crab/
Orion nebula
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What are electrons?
Electrons determine the chemical properties of
substances so how do you find out about electrons
themselves?
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Spectroscopy Electrons
Modern times
Niels Bohr unlocked their secret in 1900,
confirmed by Einstein in 1905 (Bohr had 1922
Nobel Prize in Physics awarded).
Key points to Bohrs theory

• Electrons exist in definite energy levels
• A photon of light is emitted or absorbed when
  the electron changes from one energy level to
  another
• The energy of the photon is equal to the
  difference between the two energy levels ?E, and
  related to frequency by E h ?

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What does spectroscopy do?
Monitors the wavelengths of photons absorbed or
emitted by electrons within atoms or molecules
during their transition from an excited (high
energy) state to a lower energy state.
How can it help us?
Each element emits a characteristic set of
discrete wavelengths which depends on its
electronic structure.
By observing these wavelengths the elements
present can be determined for eg. materials
analysis, astronomy. Theoretical explanations of
this process lead to quantum mechanics.
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Types of spectra
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What is happening?
Spectrum
Excited State
n4
UV
Excited State
n3
Excited State unstable and drops back down
Vi s ible
Excited State
But only as far as n 2 this time
n2

• Energy released as a photon

• Frequency proportional to energy drop

IR
Non-luminous flame or high voltage electricity to
excite atom
n1
Ground State
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Emission spectra for selected elements
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Case studyNeon
Georges Claude (24 Sept 1870 23 May 1960)
Timeline 1902 Applied electrical discharge to
sealed tube of neon gas. 1910, Paris public
display of 1st neon lamp, soon Cinzano sign
up! 1923 sold 2 signs to Packard car dealership
in Los Angeles for 24,000
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Neon gas glows with its characteristic red light
even at atmospheric pressure. There are now more
than 150 colours possible using argon, mercury
and phosphorus.
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The chemistry behind it
Looking at neon light through a diffraction
grating would show a few strong lines of colour
at a few specific wavelengths- its characteristic
emission spectrum
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Sometimes elements can be identified by the light
they absorb. The light intensity dips far down a
certain wavelengths, producing an absorption
spectrum for neon.
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Summary

• Electron normally in Ground State
• Energy supplied as heat or electricity
• Electron jumps to higher energy level
• Now in Excited State
• Unstable
• Drops back to a lower level

• Energy that was absorbed to make the jump up is
  now released as a photon
• The energy change can be calculated using E Lh?
• Frequency depends on difference in energy levels
• E2 - E1 h ?
• where h is Planks Constant and ? is frequency of
  light

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Electronic Transitions
Emission spectrum of hydrogen
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• When electron falls from a higher level to the
• n 1 level gives UV range (Lyman series)
• n 2 level gives Visible range (Balmer
  series)
• n 3 level gives Infra-red range (Paschen
  series)
• n 4 level gives Infra-red range (Brackett
  series)
• n 5 level gives Infra-red range (Pfund series)

Activity- watch the animation of electronic
transitions at
http//www.bigs.de/en/shop/anim/termsch01.swf
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Battle of the spectras
On Certain Physical Properties of Light Produced
by the Combustion of Different Metals in an
Electric Spark Refracted by a Prism
Proof of method by showing the spectral lines for
brass corresponded to those of copper and zinc
1855 Publication covering 6 gases and first
discovery of what became known as the Balmer
lines of hydrogen. Included ideas of application
to astronomy, detecting elements in shooting
stars, meteors and the daguerrotyped the suns
spectra BUT HE DIDNT GET THE CREDIT FOR IT
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The winners
1860 Robert Bunsen, Gustav Kirchoff
(Ger) Published paper recording spectra of 2
alkali metals and 6 alkaline earth metals. Showed
their presence in a variety of natural materials.
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Bunsen-Kirchhoff spectroscope with the Bunsen
burnerAnnalen der Physik (1860)
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Modern equipment
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Atomic Emission Spectroscopy
Experimental technique, main steps

• Evaporation
• Atomisation
• Excitation
• Emission

2. Atomisation Gaseous metal ions reduced to
metal atoms. Example of reaction Ca2(aq) 2e-
? Ca (g)
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3. Excitation Electrons in the metal ions absorb
energy from the heat of the flame and move from
the ground state to excited states.
Quanta of energy absorbed depends on
electrostatic forces of attraction between the
electrons and the nucleus and the energy level
that the excited electrons reach.
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4. Emission Excited electrons are very unstable
and move quickly back to the ground state. As
they do so, they emit the energy they absorbed.
This is measured in this technique.
As electrons from different energy levels absorb
different number of quanta, the energy released
is a mixture of all the different wavelengths
emitted by the different electrons in the metal
atom under investigation.
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Atomic Absorption Spectroscopy
Experimental technique, main steps

• Evaporation
• Atomisation
• Excitation
• Emission

1. Method Very similar to that of emission
spectroscopy. The main difference is that the the
quanta of energy absorbed by the substance is
measured.
2. Uses Analytical chemistry is a technique for
determining the concentration of a particular
metal element within a sample. Works for over 62
different metals in a solution.
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Excitation of electrons by

• Interaction with electromagnetic radiation in
  fluorescence spectroscopy
• With protons and heavier particles in
  particle-induced X-ray emission
• With electrons or X-ray photons X-ray
  spectroscopy or fluorescence
• Heat up sample to high temperature in flame
  emission spectroscopy

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The quantity of energy put into the flame is
known, and the quantity remaining at the other
side (at the detector) can be measured.
Hence it is possible to calculate how many of
these transitions took place, and thus get a
signal that is proportional to the concentration
of the element being measured.
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Scholar work
Topic 1 The Electromagnetic Spectrum and Atomic
Spectroscopy
1.1 Introduction 1.2 Electromagnetic
radiation 1.3 Spectroscopy 1.4 Using Spectra to
identify samples 1.5 Energy Calculations 1.6
Summary 1.7 Resources 1.8 Tutorial 1.9 End of
Topic 1 test