Transcript Shortcomings of the Bohr Model



Advanced Chemistry
Ms. Grobsky

Bohr’s model was too simple
o Worked well with only hydrogen because H only has one electron
o Could only approximate spectra of other elements with more than
one electron


Electrons do not move in circular orbits
So there is more to the atomic puzzle…

As a result of Planck’s and Einstein’s work, light was found
to have certain characteristics of particulate matter
o No longer purely wavelike
o Waveicle



But is the opposite also true?
A physicist named de Broglie asked the question:
Does matter exhibit wave properties?
The answer is Yes!
o As shown through X-ray diffraction patterns


Things that are very small behave differently from things big
enough to see
Come to find out, electrons bound to the nucleus are similar to
standing waves
o Standing waves do not propagate through space
o Standing waves are fixed at both ends
• Think of a guitar or violin
• A string is attached to both ends and vibrates to produce a musical
tone
• Waves are “standing” because they are stationary – the wave does not
travel along the length of the string
Standing Wave Video

Remember, energy is
quantized (i.e. it comes in
chunks)
o Since the energy of an atom
is never “in between”, there
must be a quantum leap in
energy

Also, a physicist named
Heisenberg stated that
“[t]here is a fundamental
limitation on how precisely
we can know both the
position and momentum of
a particle at a given time”
o It is impossible to know both
the velocity and location of
an electron at the same time


Erwin Schrodinger derived a mathematical equation that
described the energy and position of electrons in an atom
that became known as the “Quantum Mechanical Model”
An overview of the model:
o Electrons are found in energy levels and ORBITALS

Within each energy level, the complex math of Schrodinger’s
equation describes several shapes
o These are called atomic orbitals
• Orbitals are NOT circular orbits for electrons
• Orbitals ARE areas of probability for locating electrons
• Electron density maps (probability distribution) indicates the most probable
distance from the nucleus
• These DO NOT describe:
• How an electron arrived at its location
• Where the electron will go next
• When the electron will be in a particular location
• Orbitals of the same shape grow larger as number of energy levels
increases
• # of nodes (areas in which there is zero electron probability) increase as well

With a partner, complete page 204 - “Locating an ‘s’
Electron in an Atom by Analogy”
o Be sure the marbles are caught after their first bounce
o Be sure marbles are dropped from a consistent height

Change in procedure and data analysis
o No carbon paper – you must mark each landing spot with an “X”
using a pencil!
o Y-axis in graph is (# of dots/cm2)*10


Before you begin, do you expect each group to get the same
pattern?
Do you expect a marble to land exactly in the middle?
Radial Distribution (Probability)
(Dots/cm2)*10
25
20
15
10
5
0
0
2
4
6
Maximum Radial Distance
8
10



Follow along on page 205!
Atomic Orbitals Java Applet
• Spherical shape
• Single orbital
• Seen in all energy levels
• Can hold up to 2 electrons
p (x)
y-axis
z-axis
p (y)
x-axis
p (z)
• Dumbbell-shaped
• Seen in 2nd energy level and above
• Can hold up to 2 electrons PER SUBORBITAL (6 electrons total)
• Five clover-shaped orbitals
• Can hold up to 2 electrons per suborbital (10 electrons total)
• Seen in 3rd energy level and above
•
•
•
•
Seven equal energy orbitals
Each suborbital can hold up to 2 electrons (14 electrons total)
Shape is not well-defined
Seen in 4th energy level and above
 The
orbitals of an atom are LAYERED!