Transcript The Quantum Model of the Atom

The Quantum Model of the
Atom
Section 4-2
Pages 98-104
Hydrogen-Atom Line-Emission
Spectrum
• Ground state – the lowest energy state of an
atom
• Excited state – a state in which an atom has
a higher potential energy than it has in its
ground state
Continued
• Continuous spectrum – the emission of a
continuous range of frequencies of
electromagnetic radiation
• Line-emission spectrum – when a narrow
beam of the emitted light was shined
through a prism, it is separated into a series
of specific frequencies of visible light
Niels Bohr
• Danish physicist
• Proposed a model of the hydrogen atom that
linked the atom’s electron with photon emission
• Electron can circle the nucleus only in allowed
paths, orbits
• Electron can neither gain nor lose energy
• “the single electron of hydrogen orbits the nucleus
only in allowed orbits, each with a fixed energy”
Electrons as Waves
-de Broglie found that electrons have wave-like
properties:
-diffraction – bending of a wave as it
passes by the edge of an object
-interference – a reduction or increase in
energy when waves overlap
Heisenberg Uncertainty Principle: it is impossible to
determine simultaneously both the position
and velocity of an electron or any other
particle
Quantum Theory
-describes
mathematically
the wave
properties of
electrons and
other very
small particles
Atomic Orbitals and
Quantum Numbers
Orbital – three-dimensional region around the
nucleus that indicates the probable location of an
electron (each orbital can contain 2 electrons)
Quantum numbers – specify the properties of
atomic orbitals and the properties of electrons
in orbitals
Quantum Numbers
Each electron in an atom can be
characterized by four quantum
numbers. No two electrons have the
same 4 quantum numbers. These
numbers are known as the Principal,
Angular Momentum, Magnetic, and Spin
Quantum Numbers.
Principal Quantum Number
Symbolized by n, indicates the main energy level
occupied by the electron
Positive values of 1,2,3,…
As n increases, e- energy and distance from the
nucleus increase
n=1, first, or lowest, main energy level is closest to
the nucleus
Electrons with the same n value are said to be in the
same shell
Total number of orbitals per shell or main energy
level is n squared
Most general of all quantum #s; like saying, “Where do
you live,” and I answer, “in Texas.”
Angular Momentum Quantum Number
-symbolized by l, indicates the shape of the orbital
-known as a sublevel
-the # of orbital shapes possible is equal to n
-values are zero and positive integers less than or
equal to n-1 (0 = s, 1 = p, 2 = d, 3 = f)
-s orbitals are spherical; p orbitals are dumbbell
shaped; d and f orbitals are more complex
-value of n = # of sublevels. Ex: nth main energy level
is n sublevels
-each orbital is designated by its principal quantum #
followed by the letter of the sublevel. Ex: 2p = set of p
orbitals in the 2nd main energy level
-more specific such as “I live in Canyon, TX.”
Magnetic Quantum Number
-symbolized by m, indicates the orientation of an
orbital around the nucleus
-s orbital, m = 0; only one possible orientation (only one
orbital/s sublevel)
-p orbitals extend along x, y, and z axis (3-D) therefore
there are 3 orbitals/p sublevel)
-designated px, py, and pz
-m = -1, m = 0, m = +1
-d orbitals, 5/d sublevel
-m = -2, -1, 0, +1, +2
-f orbitals, 7/f sublevel
# of orbitals = n squared. Ex: 3rd energy level = 3
squared = 9 orbitals
-even more specific; like saying “I live at #3 Summit
Drive, Canyon, TX”
Spin Quantum Number
-orbitals spin on an internal axis
-two possible directions (clockwise, counterclockwise)
-spin creates a magnetic field
-only 2 possible values (+1/2, -1/2) which indicate 2
fundamental spin states of an electron in an orbital
-each orbital can hold 2 electrons, which must have
opposite spins
-maximum # of electrons per energy level = 2n
squared
Check it Out
Is this set of quantum numbers possible?
3,3,-2, -1/2
No, l must be 2 or less.
What could l be if n is equal to 5?
4, 3, 2, 1, 0