Transcript ChemChapter_4[1]Light

Chapter 4
Arrangement of Electrons
In Atoms
Properties of Light
You can treat it three ways
• Light as a wave
– Diffraction
– Interference
• Light as a particle
– Photoelectric effect
• Dual Nature of Light – light can behave as
both a wave and a particle.
– Electromagnetic Radiation – energy that
travels through space as a wave
Electromagnetic Spectrum
Wave Diagram
Wave Mechanics
• Wavelength – l – distance between
corresponding point on adjacent waves
(m)
• Frequency – n – (f) – number of waves
that pass a certain point in a given time
(waves/s) or (/s, s-1) or (Hz)
• Speed of a wave = v = ln
– For light
c=ln
(c=3x108 m/s)
Proof Light is a Wave
• Diffraction – bending of a
wave around a barrier.
• Interference – combining
of waves that cross paths
(superposition).
Proof Light is a Particle
• Photoelectric effect –
emission of electrons
from a metal when
the metal is struck by
certain frequencies of
light.
• Ean
• E = hn
– h = 6.626x10-34 Js
– Plank’s Constant
Hydrogen Emission Spectrum
E=hn
Niels Bohr – explained the
spectral lines observed in
excited gases
c=ln
n=c/l
E=hc/l
Balmer, Paschen, and Lyman Series
The DeBroglie Hypothesis
E = hn and E = mc 2
If light can behave
as both a wave
and a particle,
can electrons also
have this dual
nature?
hn = mc 2
for slower vel ocities v = c
hn = mv 2
hc
= mv 2
l
hv
l
= mv 2
hv
h
=
mv 2 mv
mv = momentum = p
h
l=
p
l=
The Quantum Model
Heisenberg’s Uncertainty
Principle – it is
impossible to know both
the exact position and the
momentum (velocity) of a
small particle at the same
time.
Schrodinger’s Wave
Equation – describes the
probability of finding an
electron at some distance
from the nucleus in terms
of the wave function Y
Implications of Heisenberg and
Schrodinger
• These ideas say it is impossible to know
where an electron is at any point in time.
Therefore we can only say where an
electron is most probably located at any
time. We call that region an orbital.
Orbital – 3d
region around
a nucleus
where an
electron is
likely to exist
Quantum Numbers – 4 numbers used to
describe the location of an electron
• Principle Quantum Number – (n) – tells the main
energy level of the electron.
• Angular Momentum Quantum Number – (l) –
describes the shape of the orbital.
• Magnetic Quantum Number – (m) – tells the
orientation of the orbital around the nucleus.
• Spin Quantum Number – (s) – indicates the
direction of the spin of the electron on its own
axis.
Pauli’s Exclusion Principle – No two
electrons have the same set of 4 quantum
numbers
• Possible values for the quantum numbers
– n = 1,2,3,…7 max # of e- in energy level =2n2
– l = n-1
l = 0,1,2,…6 or s,p,d,f,g…
– m = (-l,…0…+l)
– s = +/- 1/2
Principle Quantum Number
Tells the main energy
level (how far from the
nucleus) of an electron
#e-/energy level = 2n2
Angular Momentum Quantum Number
– Azimuthal Quantum Number
• Tells the type (shape) of the orbital
Magnetic Quantum Number – tells
orientation around the nucleus
Spin Quantum Number
s = -1/2
s = +1/2
Electron Configurations – shorthand way of
representing the arrangement of electrons in
an atom
• Pauli’s Exclusion Principle – no two electrons
have the same set of four quantum numbers
(everybody’s different)
• Aufbau Principle – electrons occupy the lowest
possible energy level (electrons are lazy)
• Hund’s Rule – orbitals of equal energy are
occupied by one electron before any one orbital
is occupied by two electrons, and all electrons in
singly occupied orbitals have the same spin
(everybody gets one before anybody gets two)
Order of Orbital Filling
Order of Orbital Filling
Electron Configurations for
1st Period
Helium ??
2+
Notations for 2nd and 3rd Periods
Orbital Notation
Orbitals Notations for 3p’s
Periodic Table with Electron
Configurations
Noble Gas Notations
Here are some examples:
O 1s22s22p4
Si 1s22s22p63s23p2
Ca 1s22s22p63s23p64s2
Cr 1s22s22p63s23p63d54s1
Br 1s22s22p63s23p63d104s24p5
La 1s22s22p63s23p63d104s24p64d104f1
5s25p66s2
O [He]2s22p4
Si [Ne]3s23p2
Ca [Ar]4s2
Cr [Ar]3d54s1
Br [Ar]3d104s24p5
La [Xe]4f 16s2.
Homework
• Pages 124-126
• Numbers
6,10,11,14,18,19,22,30,31,32,33,35,37,38,
46,48,50