Download Ch. 5 PPT Part 2

5.2 and 5.3
Bohr vs the quantum mechanical
model of the atom
5.2 and 5.3: Bohr and the quantum mechanical model
• Compare the Bohr and quantum mechanical models
of the atom.
• Explain the impact of de Broglie's wave article duality
and the Heisenberg uncertainty principle on the
current view of electrons in atoms.
• Identify the relationships among a hydrogen atom's
energy levels, sublevels, and atomic orbitals.
atom: the smallest particle of an element that retains
all the properties of that element, is composed of
electrons, protons, and neutrons.
Section 5.2 Quantum Theory and the Atom (cont.)
ground state
quantum number
de Broglie equation
Heisenberg uncertainty
principle
quantum mechanical model
of the atom
atomic orbital
principal quantum number
principal energy level
energy sublevel
Wavelike properties of electrons help
relate atomic emission spectra, energy
states of atoms, and atomic orbitals.
Review: Electrons (ground state
and excited state)
So why did we get lines in the
spectroscope?
• Niels Bohr (1885 – 1962)
• Worked with Rutherford
• Model of the hydrogen atom: the single
electron of the hydrogen atom can circle
the nucleus only in allowed paths called
orbits
• Lowest energy = closest orbit to the
nucleus
Bohr model of the atom
Bohr's Model of the Atom (cont.)
• Bohr suggested that an electron moves
around the nucleus only in certain allowed
circular orbits.
Bohr's Model of Hydrogen
Bohr's Model of the Atom (cont.)
• Each orbit was given a number, called the
quantum number.
Importance of Bohr Model
• Using charge and mass of an electron and Planck’s
constant (E=hν)
• Calculated the energies that an electron should have in
the orbits.
• Compare calculationg to the line spectrum
• The calculations were correct
• The energy that Bohr model said an electron should
have, was the same energy that the colored lines
produced from the bright line spectrum
Problem with Bohr Model
• His mathematics only applied to the
Hydrogen atom
Bohr Model of the Atom
• Bohr:
- Orbit:
- electrons were treated as:
– correctly predicted line spectrum for __________, but
could not for any other element
What to do now ??
• Bohr treated electrons like particles
• 1924: Louis de Broglie noticed that the
spectrum lines could be explained by
wave properties
• Example: waves confined in a space have
only certain frequencies.
The Quantum Mechanical Model of the Atom (
• The figure illustrates that electrons orbit the
nucleus only in whole-number wavelengths.
The Quantum Mechanical Model of the Atom
(cont.)
• The de Broglie equation predicts that all
moving particles have wave characteristics.
 represents wavelengths
h is Planck's constant.
m represents mass of the particle.
 represents frequency.
Heisenberg Uncertainty Principle
• The Heisenberg uncertainty principle states
that it is fundamentally impossible to know
precisely both the velocity and position of an
electron at the same time.
• The only quantity that can be known is the
probability for an electron to occupy a certain
region around the nucleus.
Heisenberg Uncertainty
Principle
• To see something, light must hit the object,
bounce off it, and come back to our eye
• When light hits an electron, it makes it
move because the electron is so small.
• By the time the reflected light gets back to
our eye, the electron is no longer where it
was.
The Quantum Mechanical Model of the Atom
• Using de Broglie’s and Heisenburg’s
thoughts
• Schrödinger treated electrons as waves in
a model called the quantum mechanical
model of the atom.
• Schrödinger’s equation applied equally well to
elements other than hydrogen.
Erwin Schrödinger, 1926
• Who has worked with the sin and cosine curve?
• Basically, he applied a wave formula (like sin or
cosine) to the properties of the electrons
– Worked for all atoms
– Create electron orbitals instead of orbits
– Can not pinpoint the location of the electron
The Quantum Mechanical Model of the Atom
• The wave function predicts a threedimensional region around the nucleus
called the atomic orbital.
Orbitals
Three dimensional region about the nucleus in
which a particular electron can be located
Hydrogen Atomic Orbitals (cont.)
• Each energy sublevel relates to orbitals of
different shape.
Schrodinger
• Orbitals - Mathematical representations
of where electrons could be (Not specific)
• Can not ………._______________
• Treated electrons as _________
Result of Schrodinger
• Quantum Theory
– Mathematically describes the wave properties
of electrons
– Creates orbitals which when added together,
look like an electron cloud