Transcript Brown_PPT_Tark_Ch05_part1

PowerPoint to accompany
Chapter 5
Electronic
Structure
of Atoms
Part 1
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Waves: Chemistry’s best tool

To understand the electronic structure of atoms,
one must understand the nature of
electromagnetic radiation.

The distance between corresponding points on
adjacent waves is the wavelength ().
Figure 5.3
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Waves

The number of waves
passing a given point
per unit of time is the
frequency ().

For waves travelling at
the same velocity, the
longer the wavelength,
the smaller the
frequency.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Which wave above has
the highest energy?
How can you tell?
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
b) Highest amplitude
for greatest frequency.
Energy ~ frequency
Intensity ~ Amplitude2
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Electromagnetic Radiation

All electromagnetic radiation travels at the same
velocity in vacuum.

The speed of light (c) is 3.00  108 m/s
and  = c.
Figure 5.4
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Black Body Radiation
& Optical Pyrometry
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized Energy and Photons

The wave nature of light does not
explain how an object can glow when
its temperature increases.

Max Planck explained the statistical
distribution of light, by assuming that
energy comes in packets called
quanta.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized Energy and Photons

Einstein used this assumption to explain the
photoelectric effect.

He concluded that energy is proportional to
frequency:
E = h
where h is Planck’s constant, 6.6310−34 Js.
To know frequency is to know energy!
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Potential Energy = mgh
continuous h (ramp), quantized h (steps)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
photoelectric effect
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized
Energy
and
Quantized
Energy
and
Photons
Photons

Therefore, if one
knows the wavelength
of light, one can
calculate the energy in
one photon, or packet,
of that light:
c = 
E = h
E = (hc)/
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized
Energy
and
Quantized
Energy
and
Photons
Photons
Figure 5.9
Another mystery involved
the emission spectra
observed from energy
emitted by atoms and
molecules.
Different gases have
different bright line
emission spectra (or dark
line absorbtion spectra)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized Energy and Photons:
For Matter….

One does not observe
a continuous spectrum
as one gets from a
white light source.

Only a line spectrum of
discrete wavelengths
is observed.
Figure 5.8
Figure 5.10: Sodium
versus Hydrogen
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized Energy and Photons:
Hydrogen green is visible

Figure 5.11
Niels Bohr adopted Planck’s assumption
and explained these phenomena in this
way:
1. Electrons in an atom can only
occupy certain orbits (corresponding
to certain energies).
2. Electrons in permitted orbits have
specific, “allowed” energies; these
energies will not be radiated from the
atom.
3. Energy is only absorbed or emitted
in such a way as to move an electron
from one “allowed” energy state to
another; the energy is defined by:
E = h
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Quantized Energy and
Photons
The energy absorbed or emitted from the
process of electron promotion or demotion
can be calculated by the equation:
1
(
E = −RH n
f
2
- n12 )
i
where RH is the Rydberg constant, 2.18 
10−18 J, and ni and nf are the initial and final
energy levels of the electron.
Figure 5.11
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
The Wave Nature of Matter

Louis de Broglie posited that if light can
have material properties, matter should
exhibit wave properties.

He demonstrated that the relationship
between mass and wavelength is:
h
 = mv
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
End of Chapter 5 part 1
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia