Chem 1301A Discovering Chemical Structure - All Lecture notes
(all what you need to pass this course) The University of Western
Ontario
,Lesson 1 - What is the electromagnetic spectrum?
Electromagnetic Spectrum
- Light can move as a wave (electromagnetic wave) that propagates through space as sine curves
- Wavelengths can be measured in metres, micrometres and nanometres
- Frequency is measured in hertz (closer the wavelength is, frequency is higher)
- The complete range of wavelengths λ or frequencies v of electromagnetic radiation
1. When matter interacts with light, it absorbs or emits whole photons
2. Photon energy is determined by its frequency or wavelength
Wavelengths/frequencies/energy
- Light from the sun interacts with matter, UV radiation from sun excites electrons in our skin and when they
come back down from their excitation, bonds in our DNA can break and scramble (cancer…)
,Energy of light
- Light is a stream of energy that behaves as a wave or particles
- A photon is a tiny packet of light energy
- When light interacts with matter, matter can absorb or emit photons but photons are emitted or absorbed in
WHOLE units not fractions (not parts)
- Ex. when water is heated up in the microwave, water particles interact with microwave radiation
Our eyes
- Our eyes can only detect approx. 400 to 750 nanometers of light
- Have cones and rods which have a protein called rhodopsin and the little molecule in the protein is
11-cis-retinal (aldehyde functional group)
- Cis interacts with wavelengths of 500 nanometers so when light hits, it flips to its trans state and changes the
shape of the molecule and sends a signal to your brain to perceive your sight
Spectroscopy Equipment
- MRI Spectrometer: Magnetic resonance imaging (can detect water and fatty tissue inside the body
- NMR Spectrometer: Nuclear magnetic resonance (chemical applications inside a test tube, similar to MRI but
lab work)
- UV/Visible Spectrophotometer: Ultraviolet Visible Light Absorbance (can measure the uv and visible
absorption of a sample ex. Sunscreen
Lesson 2 - What led to the development of the first model of the atom?
Dalton
- 1808 shared his first theory of the atom that all matter is made up of tiny particles
Emission spectrum of atomic hydrogen
- Physicists were playing with a tube of DIATOMIC hydrogen then discovered that when H2 gas is placed in a
tube and excited with a high-voltage electric discharge, H2 molecules dissociate into excited H atoms and the
atoms emit light with certain wavelengths
- Hydrogens split apart and the atomic “excited” hydrogen then passes through a prism projecting rainbow
colours of light (balmer series)
- Transitions from different levels of energy:
- Balmer series are the spectral lines (higher wavelength, 700nm, is lower towards nucleus)
- Lyman discovered that electrically excited hydrogen atoms emit not only visible light, but also UV light
- Pachen series is discrete wavelengths of infrared light emitted by hydrogen atoms
- When n=1, m=2,3…
- When n=2, m=3,4… so on
, The bohr model of the hydrogen atom
- He proposed that the electron in the hydrogen atom moves about the nucleus in a circular orbit (only certain
orbits are possible)
- The energy of the electron in each orbit is “quantized”
- He assigned each orbit an energy level n=1,2,3…
- n=1 is closest to the nucleus (ground state)
- Higher energy the further away from nucleus (negative)
- DRAWBACKS:
- Did not explain how the electron can remain in the lowest-orbit
- When H emission spectrum was enlarged, it turned out that each line actually consisted of two closely
spaced lines
- How do we explain splitting?
- Why doesn't it work for any other element?
Lesson 3 - How do electrons behave as waves?
Bohr theory unexplained
- Electrons were strictly treated as particles however, they do behave like waves but it was unexplained
- Why does the electron in the first orbit remain on the ground state
Light through a small hole
- Propagating wave will fill the space behind the hole which is called diffraction
- This redirects the propagating wave
- Multiple holes will lead to diffraction but it will also create interference patterns
- Helps distinguish particle and wave behaviour because we generate interference patterns
Interference
- Constructive interference: two interacting waves are “in phase” results in a wave with an amplitude of two
waves (strong amp, increase in intensity)
- Destructive interference: when two interacting waves are in opposite phases results in zero amplitude (cancel
out)
Photoelectric effect - the action of light on a material where electrons are ejected
- Einstein determined that light contained a huge number of photons that had discrete quantities of energy.
These were related to the frequencies of light.
Louis de Broglie
- “Wave particle duality”
- Related the mass and velocity of a particle to its wavelength
- Suggested that electrons might exhibit wave-like behaviour in addition to its already proposed
qualities
- He then proposed this equation relating mass and velocity of a particle to its wavelength
(all what you need to pass this course) The University of Western
Ontario
,Lesson 1 - What is the electromagnetic spectrum?
Electromagnetic Spectrum
- Light can move as a wave (electromagnetic wave) that propagates through space as sine curves
- Wavelengths can be measured in metres, micrometres and nanometres
- Frequency is measured in hertz (closer the wavelength is, frequency is higher)
- The complete range of wavelengths λ or frequencies v of electromagnetic radiation
1. When matter interacts with light, it absorbs or emits whole photons
2. Photon energy is determined by its frequency or wavelength
Wavelengths/frequencies/energy
- Light from the sun interacts with matter, UV radiation from sun excites electrons in our skin and when they
come back down from their excitation, bonds in our DNA can break and scramble (cancer…)
,Energy of light
- Light is a stream of energy that behaves as a wave or particles
- A photon is a tiny packet of light energy
- When light interacts with matter, matter can absorb or emit photons but photons are emitted or absorbed in
WHOLE units not fractions (not parts)
- Ex. when water is heated up in the microwave, water particles interact with microwave radiation
Our eyes
- Our eyes can only detect approx. 400 to 750 nanometers of light
- Have cones and rods which have a protein called rhodopsin and the little molecule in the protein is
11-cis-retinal (aldehyde functional group)
- Cis interacts with wavelengths of 500 nanometers so when light hits, it flips to its trans state and changes the
shape of the molecule and sends a signal to your brain to perceive your sight
Spectroscopy Equipment
- MRI Spectrometer: Magnetic resonance imaging (can detect water and fatty tissue inside the body
- NMR Spectrometer: Nuclear magnetic resonance (chemical applications inside a test tube, similar to MRI but
lab work)
- UV/Visible Spectrophotometer: Ultraviolet Visible Light Absorbance (can measure the uv and visible
absorption of a sample ex. Sunscreen
Lesson 2 - What led to the development of the first model of the atom?
Dalton
- 1808 shared his first theory of the atom that all matter is made up of tiny particles
Emission spectrum of atomic hydrogen
- Physicists were playing with a tube of DIATOMIC hydrogen then discovered that when H2 gas is placed in a
tube and excited with a high-voltage electric discharge, H2 molecules dissociate into excited H atoms and the
atoms emit light with certain wavelengths
- Hydrogens split apart and the atomic “excited” hydrogen then passes through a prism projecting rainbow
colours of light (balmer series)
- Transitions from different levels of energy:
- Balmer series are the spectral lines (higher wavelength, 700nm, is lower towards nucleus)
- Lyman discovered that electrically excited hydrogen atoms emit not only visible light, but also UV light
- Pachen series is discrete wavelengths of infrared light emitted by hydrogen atoms
- When n=1, m=2,3…
- When n=2, m=3,4… so on
, The bohr model of the hydrogen atom
- He proposed that the electron in the hydrogen atom moves about the nucleus in a circular orbit (only certain
orbits are possible)
- The energy of the electron in each orbit is “quantized”
- He assigned each orbit an energy level n=1,2,3…
- n=1 is closest to the nucleus (ground state)
- Higher energy the further away from nucleus (negative)
- DRAWBACKS:
- Did not explain how the electron can remain in the lowest-orbit
- When H emission spectrum was enlarged, it turned out that each line actually consisted of two closely
spaced lines
- How do we explain splitting?
- Why doesn't it work for any other element?
Lesson 3 - How do electrons behave as waves?
Bohr theory unexplained
- Electrons were strictly treated as particles however, they do behave like waves but it was unexplained
- Why does the electron in the first orbit remain on the ground state
Light through a small hole
- Propagating wave will fill the space behind the hole which is called diffraction
- This redirects the propagating wave
- Multiple holes will lead to diffraction but it will also create interference patterns
- Helps distinguish particle and wave behaviour because we generate interference patterns
Interference
- Constructive interference: two interacting waves are “in phase” results in a wave with an amplitude of two
waves (strong amp, increase in intensity)
- Destructive interference: when two interacting waves are in opposite phases results in zero amplitude (cancel
out)
Photoelectric effect - the action of light on a material where electrons are ejected
- Einstein determined that light contained a huge number of photons that had discrete quantities of energy.
These were related to the frequencies of light.
Louis de Broglie
- “Wave particle duality”
- Related the mass and velocity of a particle to its wavelength
- Suggested that electrons might exhibit wave-like behaviour in addition to its already proposed
qualities
- He then proposed this equation relating mass and velocity of a particle to its wavelength
