-The Bohr Model -The Quantum Mechanical Model Warner SCH4U Chemistry.
From the Bohr Model to the Quantum Mechanical Model
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From the Bohr Model to the Quantum Mechanical Model Advanced Chemistry Ms. Grobsky
description
From the Bohr Model to the Quantum Mechanical Model. Advanced Chemistry Ms. Grobsky. Shortcomings of the Bohr Model. Bohr’s model was too simple Worked well with only hydrogen because H only has one electron C ould only approximate spectra of other elements with more than one electron - PowerPoint PPT Presentation
Transcript of From the Bohr Model to the Quantum Mechanical Model
From the Bohr Model to the Quantum
Mechanical ModelAdvanced Chemistry
Ms. Grobsky
Shortcomings of the Bohr Model 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…
de Broglie and the Dual Nature of Light
As a result of Planck’s and Einstein’s work, light was found to have certain characteristics of particulate mattero No longer purely wavelikeo 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
Quantum Mechanical Model of the Atom
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 waveso Standing waves do not propagate through spaceo 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 stringStanding Wave Video
The Quantum Mechanical Model
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
The Quantum Mechanical Model
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
Atomic Orbitals Within each energy level, the complex math of
Schrodinger’s equation describes several shapeso 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
Electron Density Maps??? WHAT?????
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 bounceo Be sure marbles are dropped from a consistent height
Change in procedure and data analysiso 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?
Sample Marble Drop Probability
0 1 2 3 4 5 6 7 8 90
5
10
15
20
25
Maximum Radial Distance
Radi
al D
istr
ibut
ion
(Pro
b-ab
ility
)(D
ots/
cm2)
*10
So What do These Probability Distributions (Atomic Orbitals) Look
Like?
Atomic Orbitals Simulation
Follow along on page 205!Atomic Orbitals Java Applet
The s-Orbital
• Spherical shape• Single orbital• Seen in all energy levels• Can hold up to 2 electrons
The p-Orbital
p (z)
p (y)
p (x)
x-axis
y-axis
z-axis
• Dumbbell-shaped• Seen in 2nd energy level and above• Can hold up to 2 electrons PER SUBORBITAL (6 electrons
total)
The d-Orbital
• Five clover-shaped orbitals• Can hold up to 2 electrons per suborbital (10 electrons total)• Seen in 3rd energy level and above
The f-Orbital
• 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
Summary of Atomic Orbital Shapes
Arrangement of Atomic Orbitals
The orbitals of an atom are LAYERED!
