Download Section 5.2 Quantum Theory and the Atom

Section 5.2 Quantum Theory and the Atom
• 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.
Bohr's Model of the Atom
• Bohr correctly predicted the frequency lines in
hydrogen’s atomic emission spectrum.
• The lowest allowable energy state of an atom
is called its ground state.
• When an atom gains energy, it is in an
excited state.
Bohr's Model of the Atom (cont.)
• Bohr suggested that an electron moves
around the nucleus only in certain allowed
circular orbits.
•
http://www.colorado.edu/physics/2000/quantumzone/bohr.html
Bohr's Model of the Atom (cont.)
• Each orbit was given a number, called the
quantum number.
Bohr's Model of the Atom (cont.)
• Hydrogen’s single electron is in the n = 1
orbit in the ground state.
• When energy is added, the electron moves to
the n = 2 orbit.
Bohr's Model of the Atom (cont.)
Bohr's Model of the Atom (cont.)
Bohr's Model of the Atom (cont.)
• Bohr’s model explained the hydrogen’s
spectral lines, but failed to explain any
other element’s lines.
• The behavior of electrons is still not fully
understood, but it is known they do not move
around the nucleus in circular orbits.
The Quantum Mechanical Model of the Atom
• Louis de Broglie (1892–1987)
hypothesized that particles, including
electrons, could also have wavelike
behaviors.
The Quantum Mechanical Model of the Atom
(cont.)
• The de Broglie equation predicts that all
moving particles have wave characteristics.
λ represents wavelengths
h is Planck's constant.
m represents mass of the particle.
ν represents frequency.
The Quantum Mechanical Model of the Atom
(cont.)
• Heisenberg showed it is impossible to take
any measurement of an object without
disturbing it.
• The Heisenberg uncertainty principle
states that it is fundamentally impossible to
know precisely both the velocity and position
of a particle 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.
The Quantum Mechanical Model of the Atom
(cont.)
• 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.
The Quantum Mechanical Model of the Atom
(cont.)
• The wave function predicts a threedimensional region around the nucleus
called the atomic orbital.
•
Show Teacher’s Domain Video
Hydrogen Atomic Orbitals
• Quantum Numbers:
• Each electron within an atom can be
described by a unique set of four
quantum numbers.
• Principal Quantum Number (n):
energy level (1 to 7) (size or diameter of
cloud). (fig 5.16 p. 153) Electrons may
be found at any level. The greatest
number of e- at any level = 2n2.
•
Energy sublevels (l): (shape of cloud)
Number of sublevels possible is equal to
the principle quantum number. If n=1,
then only 1 sublevel. If n=2, then 2
sublevels, and so on. Sublevels are
s,p,d, and f. The s sublevel is the lowest
energy, p is 2nd, d is 3rd, and f is the
highest. (shape is shown in fig. 5-10 & 511 p. 121)
Hydrogen Atomic Orbitals (cont.)
• Energy sublevels are contained within the
principal energy levels.
•
Orbital (m): (direction in space) X, Y, Z
coordinates. (Maximum of 2 electrons
per orbital) – see diagrams next slide
Hydrogen Atomic Orbitals (cont.)
• Each energy sublevel relates to orbitals of
different shape.
•
Spin quantum (s): rotation clockwise or
counter clockwise. Indicated by arrow
either up or down . (+ ½ or - ½)
Orbitals http://www.youtube.com/watch?NR=1&v=9E3QaRxqXZc&feature=fvwp
Hydrogen Atomic Orbitals (cont.)