Download Chapter 4 Arrangement of Electrons in Atoms

Chapter 4
Arrangement of Electrons in
Atoms
Light can act as a ______________….
λ = wavelength
(lambda)
ν = frequency
# waves/sec
(nu), measured in
Hertz, Hz = 1/s
c=λν
• c = speed of light (3.0 x 108 m/s)
• What is the frequency of a beam of red
light whose wavelength = 659 nm?
What is the frequency of a
beam of red light whose
wavelength = 659 nm?
•
•
•
•
c=λν
___________ m/s =___________
_____________ = _____________
ν = ____________1/s =___________
_________ _____________ is the
only electromagnetic (EM) radiation
we can see
• electromagnetic radiation (EM):
form of energy that travels through
space as a __________
Light can also act as a ____________
• Supported by 2 experiments:
–Photoelectric effect
–Hydrogen atom spectrum
Particle description of light
• Max Planck, 1900 – studied ___________
of light by hot objects
• Proposed that energy is not
____________ continuously but in small
little ___________ called
_____________ – This is a particle
property
• “quantum”: min am’t of energy than can
be lost or gained by an atom
• Energy  _______________
Planck proposed the following
relationship between a quantum of
energy and its frequency of radiation:
• Energy  frequency
• E=
( frequency )
• where h = Planck’s constant
6.626 x 10-34 J • s (or J/Hz)
Duality of light explained
photoelectric effect!
Metal must be struck by a
photon possessing a min.
am’t of E – below this am’t,
the electron won’t leave the
metal! More light of the
same
E (same ν) just released
more electrons…not more
energetic
• Ground state: atoms whose electrons
are in their ___________ energy level
• Excited state: an atom,having
__________ E, jumps its electron(s)
to a higher E level. The electron must
jump completely from one level to
another.
• De-excitation: after a short time the electron
____________________________ and _____
a photon (packet of E) equivalent to the energy
difference between the 2 steps. The photon
will produce a spectral line with a discrete
wavelength (color) associated with it.
• Continuous spectrum:all wavelengths are
present (i.e.sunlight)
• Emission (bright line) spectrum: limited # of
specific bright lines that are produced by pass
the light emitted by an excited atom through a
prism
• Absorption (dark line) spectrum:
light emitted by an excited atom passes
through a substance that filters out
certain wavelengths and thus produces
a spectrum with missing (dark) lines.
• Bright lines of an emission spectrum
are _____________________ as the
dark lines of an absorption spectrum
for a given element.
Bohr Model of the Atom, 1913
• Studied the absorption of light by ___________
• Absorption of light at definite wavelengths
corresponds to the definite changes in the E of the
_______________
• Electrons can circle the nucleus at ___________
_____________ distances…only in allowed paths,
or orbits (Satellite model)
• Energy of an electron is ____________ when it is in
orbits farther away from the nucleus
• His calculated energy values agreed with the
observed spectral lines for hydrogen
• Model did NOT work when applied to multielectron elements 
Duality of light
• Proposed by Einstein after studying the works
of Planck and Bohr
• Light has been traditionally thought of as a
__________ (it has freq. & wavelength)
• But now.. light can also be thought of as a
__________ ___ ______ of particles called
photons
• photons: particle of EM radiation having
_______ mass and carrying a ______________
of energy
• Explained photoelectric effect: EM radiation is
absorbed only in whole numbers of photons
4-2
The Quantum Model of the
Atom
De Broglie, 1924
• If light could behave as both a wave and a particle,
then could an electron (a particle) also behave as
both a particle and a wave ?????????????
• He said “_________” because….
– Since electrons could only exist at specific energies, and
E can be equated to frequency (E = hν), they have
wave properties
– And electrons can be “focused” like light
(electron microscopes)
– particle nature of electrons had already been
confirmed (cathode rays, oil drop exper, etc.)
• Electrons have a dual
wave-particle nature
Heisenberg Uncertainty Principle
• It is impossible to determine
simultaneously both the __________
and __________ of an electron or
any other particle
Schrodinger Wave Equation, 1926
• If electrons have wave properties, then wave
equations can be applied to electrons (and
other small particles)
• Laid foundation for __________
___________: describes
______________________ the wave
properties of electrons and other very small
particles
• Gives the ______________________ of
finding an electron at a given place in time
around the nucleus
Quantum Theory (con’t)
• Electrons do NOT travel around the
nucleus like planets around the sun
• Electrons exist in certain regions called
______________: a 3-D region around
the nucleus that indicates the _________
location of an electron
Quantum Numbers
• Specify the properties of atomic
orbitals and the properties of
electrons in orbitals
• There are __________ quantum
numbers….the first three of which
come from solutions to
Schrodinger’s wave equation
Principal Quantum Number, n
• Indicates the _________ __________
_________ (or shell) occupied by the electron
• n = 1, 2, 3 etc.
• The ↑n value, the ___________ the electron is
from nucleus∴ principal quant # also gives
________ ________________
• Total # electrons on a level = __________
• Total # orbitals on a level = n2 since an orbital
can hold two electrons (2n2/2= n2)
Angular Momentum Quantum
Number, l
• Also known as “second quantum number”
• Also known as “azimuthal quantum number”
• Most energy levels (all but n=1) have orbitals of
different __________, called ____________
• Describes the ______________ of the orbital
• # orbital shapes possible is equal to the
______ _____________
– If n=3, then there can be 3 orbital shapes
• The values of l = 0, 1, 2,……. (n-1)
– If n=3, then l can be ___, ___, or ___.
Angular Momentum Quantum
Number, l (con’t)
• An orbital LETTER is used to designate
each shape:
L value
Letter designation
0
s (spherical)
1
p (dumbbell)
2
d (complex - p.102)
3
f (too complex for here)
Energy level,
n
# sublevels
2nd quant #
Letter
denotation
Magnetic Quantum Number, ml
• also known as the 3rd quantum
number
• indicates the orientation of an
orbital around the nucleus
• = (2 l + 1)
Magnetic Quantum Number, m (con’t)
• Sum of all orbitals in a sublevel (or E
level) is a spherical cloud!
Orbital shape
# orientations
s
1
p
3
d
5
f
7
Spin quantum number, s
• Describes the spin of the electron
• Could be either clockwise ( + ½) or
counterclockwise (- ½ )
• Each orbital can hold a maximum of two
electrons, a pair, spinning in opposite
directions
4-3
ELECTRON
CONFIGURATIONS
Hund’s Rule
• Orbitals of equal energy are ________
occupied by one electron before any
orbital is occupied by a second electron,
and…
• All electrons in singly occupied orbitals
must have the same _____
Aufbau Principle
• An electron occupies the
________________ orbital that
can receive it
Noble Gas Notation
• What is the noble gas electron notation
for calcium?
• 1s22s22p63s23p64s2
• What is the noble gas config for S?
• 1s22s22p63s23p4
PREDICTED