chapter 3 part ii how are the electrons arranged around the nucleus?
TRANSCRIPT
Chapter 3 Part II
How are theelectronsarranged
around thenucleus?
Normal or Rest Position
Crest
Wavelength Amplitude
Amplitude
Wavelength Trough
3
Parts of a Wave
Parts of a WaveA. Amplitude: Height of the wave. The higher
the wave the greater the intensity.
B. Wavelength: (λ , “lambda”) in nanometers (1 x 10-9 m) measured from crest to crest or from trough to trough.
C. Frequency: (ν , “nu”) The number of times a wave passes a fixed point. Measured in cycles/second (1/s) 1 cycle/second = Hertz (Hz)ex) Radio FM 93.3 megahertz (MHz) is 93.3 x 106
cycles/sec.
Visible Light
Radar
Microwaves
Infrared
Radio/TV Ultraviolet
X-Rays
Gamma Rays
Low
Long
High
Short
Red Orange Yellow Green
Blue Indigo Violet
Energy
Energy
Low High
The Electromagnetic Spectrum
Speed of Light
D. (c) 3.0 x 108 m/s or 186,000 miles/sec. The relationship between wavelength and frequency can be shown with the
following equations:
or this is an indirect relationship.
If λ then ν .
cλ= νcν =λ
Quantum Theory
A. Planck’s Hypothesis: (Max Planck 1900)
1. An object absorbs or emits light in
little packet or bundle called a quantum (quanta –plural).
2. Energies are quantized. (Think steps not a ramp.)
3. Equation relating energy (E) to frequency (ν, nu) (h= Planck’s Constant)
E = h This is a direct relationship,
as ν , E
e-
e- Xe-
e-
Light (Electromagnetic Radiation)
1. A quantum of light is called a photon.2. Light travels through space in waves.3. Light acts like a particle when it interacts
with matter.4. This shows the Dual Nature of Light.
3. The AtomA. Atomic Emission Line Spectra: contains
only certain colors or wavelengths ( ) of light.
1. Every element has its own line spectrum (fingerprint).
Double Slit Experiment
Double Slit Experiment Video
This Experiment Proves the Dual Nature of Light – Photons of Light
travel through spaces in waves, but act like particles when they interact
with matter.
Continuous Spectrum – White Light
Line Spectrum – Excited Elements
Line Emission Spectra of Selected Elements
Gas Discharge Tubes
• Electricity is added to the gas which causes the electrons to jump to a higher or excited state. They immediately fall back to the ground state and give off particular wavelengths of light. We see a blending of wavelengths without the spectroscopes.
White Light gives off a Continuous Spectrum
a blending of every possible wavelength
Spectroscope• Uses a diffraction grating to diffract the
light into particular wavelengths of light.
A Line Spectrum results from excited elements - as electrons of an element gain
energy and rise to an excited state they then fall back to their ground state in the same
pattern producing the same energy drop each time which we see as individual wavelengths
of light.
Atomic Spectra
Hydrogen
Lithium
Mercury
Helium
Although Bohr’s atomic model explained the line spectra of hydrogen, it failed for heavier elements.
B. Bohr Model of Hydrogen: (1911)
1. Bohr said the energy of an electron was quantized (only certain orbits that represented different amounts
of energy.)
2. Bohr labeled each energy level with a quantum number (n).
3. n=1 lowest level or ground state.
4. When electrons absorb energy they jump to a higher (excited) state. n=2 n=3 n=4 n=5 n=6 n=7
5. Radiation (light) is emitted when an electron falls back from
a higher level to a lower level.
Electrons release energy as they fall back to a lower
energy level
Excited Atoms Emit Photons of Light:
Electrons absorb energy to rise to a higher or excited state and emit energy in the form of a photon of light as they fall back to their
ground states.
Path of an excited electron as it “falls” back to the Ground State
• When electrons gain energy, they jump to a higher energy level (excited state).
• Electrons are not stable at the excited state and will immediately fall back to a lower level or ground state.
• As they fall, they emit electromagnetic radiation.
• Depending on how far they fall determines the type of radiation (light) released.
electrons fall to n = 1 and give off ultraviolet light.
electrons fall to n = 2 and give off visible light.
electrons fall to n = 3 and give off infrared light.
Hydrogen Atom
Ultraviolet Light
Visible Light
Infrared Light
Werner Heisenberg: (1927)
1. Heisenberg’s Uncertainty Principle: states the
position and momentum (speed, direction & mass) of
a moving object cannot simultaneously be measured and known exactly.
2. You cannot predict future locations of particles.
3. He found a problem with the Bohr Atom - no way to observe or measure the orbit of an electron.
4. Quantum Mechanics
A. Quantum Mechanical Model of the atom combines previous ideas and treats the electron like a wave that has quantized
energy.
Impossible to state the exact position or momentum of an electron, but you can state a probability of where the electron is located.
B. Electron Density
Where the density ofan electron cloud ishigh there is a highprobability that iswhere the electron islocated. If the
electrondensity is low then there is a lowprobability.
C. Atomic Orbitals - region around the nucleus where an electron with a given energy is likely to be found (not the same as Bohr’s orbits!)
1. Orbitals have characteristic shapes, sizes, &
energies.2. Orbitals do not describe how the electron
moves.3. The drawing of an orbital represents the
3-dimentional surface within which the electron is found 90% of the time.
4. Sublevels can have 4 different shapes
s – orbital spherical
1s, 2s & 3s orbitals Superimposed on one another
Electron-Cloud Models
p-orbital – dumbbell shaped
p-orbital - dumbbell shaped
d-orbital - double dumbbell or fan blades
s,p and d orbitals
For a more complete representation and presentation of atomic orbitals go to http://winter.group.shef.ac.uk/orbitron/
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
x
y
z
s orbital p orbitals
d orbitals
Models of d-orbitals
f-orbital – more
complex!
Quantum Numbers - Finding an address for each
electron:1) “state” Principle Quantum Number (n) or
the energy level ranges from n=1 to n=7
2) “city” Sublevel shape either s, p, d,or f.
3) “street” Orbital The orientation in space ex) x,y,z axis
4) “house” Spin The cw or ccw motion of electrons.
1s, 2s,2p and 3s orbitals superimposed on each other
• Model of s and p Orbitals Together
2. The number of Sublevels in an energy level
equals the Principle Quantum Number (n).
3. Orbital: There are always an odd number of orbitals.
s-sublevel has 1 orbitalp-sublevel has 3 orbitalsd-sublevel has 5 orbitalsf -sublevel has 7 orbitals
• Orbitals in higher principle levels get larger.• A max of 2 electrons fit in each orbital.
Electron Spin
a. Two electrons in each orbital have opposite
spins. (clockwise and counterclockwise)
b. The opposite spin is written: or ___
c. Pauli Exclusion Principle:
1. Each orbital can only hold 2 electrons.
2. The electrons must have opposite spins.
s-sublevel = max 2 electronsp-sublevel = max 6 electronsd-sublevel = max 10 electronsf-sublevel = max 14 electrons
incorrect: ↑↑↑ incorrect: ↑↑ correct: ↑↓
d. Hund’s Rule:• Electrons will
spread out among the orbitals before they pair up.
incorrect ↑↓ ↑ __
correct ↑ ↑
↑
E. Electron Configurations:
1. Shows the distribution of electrons among the orbitals. Describes where the electrons are found & what energy they possess.
2. The Aufbau Principle: electrons are added up one at a time to the lowest energy orbital.
Aufbau Diagram/ Diagonal Rule
Electron Configuration Examples:
Ex) electron configuration for Na:
1s2 2s2 2p6 3s1
Ex) orbital filling box diagram for Na:
yx z
1s 2s 2p 3s
_
3. Electron Dot Diagrams:
Write the symbol for the element.
Place dots around the symbol to represent the
valence s & ps & p electrons only.
Do NOT include d & f orbitals in diagram.
p orbital electrons s orbital electrons
Electron Configuration
Aufbau Diagram Order
Aufbau Diagram
Visualizing The Electron~
Model of Bohr Atom - Electron Movement
Line Emission Spectra of Selected Elements
The Aufbau Principle(Diagonal Rule)
1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f14
6s2 6p6 6d10 6f14
7s2 7p6 7d10 7f14
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
Pauli Exclusion Principle: No more than 2 e- are put in each orbital and they must have opposite spin.Hund’s Rule: electrons spread out among equal energy orbitals in a sublevel (like charges repel)Aufbau Principle: Electrons fill lowest energy levels first (n=1)
Electron Blocks on the
Periodic Table
Electron Configuration Orbital Box Diagram Electron-dot Diagram
yx z
1s 2s 2p
y yx z x
1s 2s 2p 3s 3p
z
168O
3517 Cl 1s22s22p63s23p5
12752Te 1s22s22p63s23p64s23d104p65s24
d105p4
1s22s22p4
y y y yx z x z x z x z
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
What does the Tellurium electron-dot resemble???
The Copper Atom
Mark your Periodic Tables
1 2 13 14 15 16 17 18
Scanning Tunneling Microscope
In 1926, Erwin Schrodinger derived an equation that described the energy and
position of the electrons in an atom
22
2 2
8dh EV
m dx
Equation for the probabilityprobability of a single electron being found along a single axis (x-axis)
Erwin SchrodingerErwin Schrodinger