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Unit #4
CP Chemistry
 Bohr
 Quantum
Numbers
 Quantum Mechanical Model
 Bohr
worked with the concepts of energy,
wavelength and frequency
 Each color of light is associated with a
different energy
 Each atom gives off its own unique color so..
 Electrons of different atoms have different
energies
 Each
atom has its own specific electron
arrangement
 Electrons are in Energy levels in the atom
 When an electron goes from an excited state
back down to its ground state the atom emits
light
n=4
n=3
n=2
n=1
 Doesn’t
work.
 Only works for hydrogen atoms.
 Electrons don’t move in circles.
 The quantization of energy is right, but not
because they are circling like planets.
 Back to the drawing board
 Valence
electrons- the electrons in the
outermost energy levels (not d).
 Core electrons- the inner electrons
 Ground state – all electrons are on the lowest
possible energy levels
 Excited State – some electrons have more
energy than usual, causing some electrons to
be in a higher energy level than they should
be in
 Electromagnetic
radiation is a form of
energy that exhibits wavelike behavior as it
travels through space
 Organized on the Electromagnetic Spectrum
according to wavelength and frequency
Wavelength (l) = Length of one wave
Measured in unit of distance (m, nm, etc.)
l
Frequency(v) = number of cycles in one second
Measured in hertz 1 hz = 1 cycle/second
 There
are many
 Different l and n
 Higher Energy = Higher Frequency / Lower
Wavelength
 Radio waves, microwaves, x rays and gamma
rays are all examples.
 Visible Light is only the part our eyes can
detect.
Radio
amma
Rays
waves
 As
we know, the amount of energy is related
to the wavelength
 Different wavelengths will show different
colors
 Each element gives off it own unique set of
colors
 Therefore each element gives off its own
unique amount of energy
 Electrons
are constantly in motion and give
off energy when they move from an excited
state to ground state
 Planck
A
A
found energy came in packets
Packet of energy is called a quantum
quantum is the minimum amount of energy
that can be gained or lost by an atom
 Einstein
said that light can be viewed as a
stream of particles called photons
A
Photon is a particle of radiation with zero
mass and carrying a quantum of energy
 Is
energy a wave like light, or a particle?
 Yes
 Concept
 What
 Yes,
is called the Wave -Particle duality.
about the other way, is matter a wave?
hence the quantum mechanical model
 Each
element has a specific number of
electrons
 In an atom electrons are arranged in a
specific arrangement
 We know this because each element has
its own atomic spectra
 Different energy = different colors=
different electron arrangement
A
totally new approach.
 De Broglie said matter could be like a wave,
like standing waves.
 The vibrations of a stringed instrument.
 How
we keep track of electrons
 Principal quantum number (n) energy level of
the electron.
 Is a number from 1-7
 Angular
momentum quantum number (l)
gives the shape of the orbital
 Has values between 0 and n-1
S orbitals
l=0
1 orbital per energy level
P orbitals
l=1
3 orbitals per
energy level
D orbitals
l=2
5 orbitals
per energy
level
F Orbitals
l=3
7 orbitals per
energy level
F orbitals
 Magnetic
 Takes
quantum number (m )
I
a guess at what orbital the electron is
in
 Gives the axis orientation
 Tells direction in each shape (x,y,z)
 Is
a value between – l and + l
 Electron
 Can
spin quantum number (m )
have 2 values.
 either +1/2 or -1/2
s
We follow 3 rules to get the correct electron
configuration for each atom
1.
2.
3.
Aufbau Principle
Pauli exclusion Principle
Hund’s Rule
 Aufbau
is German for building up.
 As electrons are added to the atom they
arrange themselves in orbitals
 The orbitals are in order of lowest energy
(1s) to the highest energy
 The order of the triangle
 Fill up in order of energy levels.
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
56
• 38
20electrons
4212
 Only
2 electrons per orbital
 Electrons in the same orbital must have
opposite spins
 Spin is represented by an arrow
 Hund’s
Rule- The lowest energy configuration
for an atom is the one that has the maximum
number of unpaired electrons in the orbital.
2 2 2
 C 1s 2s 2p
Increasing energy
7s
6s
5s
7p
6p
5p
4p
4s
6d
5d
4d
3d
3p
3s
2p
2s
1s
He with 2
electrons
5f
4f