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Chapter 4
Arrangements of Electrons
Properties of Light as a Wave
Electromagnetic radiation –
form of energy that exhibits
wave-like behavior as it travels
through space
Measurements Involving Waves
Wavelength (m, cm, nm) –
the distance between two
consecutive peaks in a
wave.
Symbol = l
(lambda)
Frequency (Hz, 1/s) –
the number of waves that
pass a given point in a
specific time, usually one
second.
Symbol = n
(nu)
Wavelength
Electromagnetic Spectrum
Visible Spectrum
R
O
Y
G
B
I
V
Indigo has been dropped so now it’s:
ROY G. BV
Relationships
All electromagnetic radiation travels at the
speed of light:
3x108m/s
Or 186,000 mps
Mathematical relationship between frequency and
wavelength:
c = ln
(c=speed of light)
Electromagnetic Waves
http://www.colorado.edu/physics/2000/waves_particles/index.html
Relationships
Frequency, Wavelength, and Energy
Frequency and Wavelength
increases,
As the frequency of a wave
the wavelength
decreases.
Therefore these properties are
inversely
related.
Frequency and Energy
As the energy of a wave
the frequency
increases,
increases.
Therefore these properties are
directly
related.
Wavelength and Energy
These properties must be
inversely
related.
http://www.ifae.es/xec/phot2.html
Photoelectric Effect
Photoelectric effect Applet
http://zebu.uoregon.edu/2000/ph101/lec06.html
Refers to the emission of electrons from a
metal when light shines on the metal.
Light had to be a certain wavelength to
cause electrons to be emitted.
This caused scientists to question the wave
nature of light.
Properties of Light as a Particle
Max Planck – Energy is emitted in small, specific
amounts called quanta.
Quantum - minimum quantity of energy that
can be lost or gained by an atom.
Photon – particle of electromagnetic radiation
having zero mass and carrying a quantum of
energy.
E = hn
Energy = Planck’s constant (6.626x10-34Js) times frequency
Wave-Particle Duality
Einstein – electromagnetic radiation
(light) exhibits both wave and
particle behavior.
While light exhibits many wavelike
properties, it can also be thought of
as a stream of particles.
Energy and Electrons
Bohr model of the atom
the planetary model where the nucleus is orbited by
electrons at different energy levels like planets around the
sun
Ground state
lowest energy state of an atom
(electrons occupy lowest energy level available)
Excited state
state in which an atom has a higher potential energy than
it has in its ground state
(electrons are in higher levels when lower levels are
available)
Energy Transitions
When a quantum of energy hits
the atom an electron can
jump energy levels to an
excited state.
When an excited electron falls
back down from its excited
state to the ground state, it
emits a quantum of
electromagnetic energy
equal to the amount that it
took to get it there.
Energy absorbed
Energy emitted
Excited
Ground State
Emission
Continuous spectrum – the complete
electromagnetic spectrum
including all forms of energy. (Ex:
rainbow)
Line-emission spectrum – when an
atom is energized and the light
given off is passed through a
prism, a series of light with specific
energy is emitted.
Elemental Line Emission Spectrums
Hydrogen
Line emissions
Location of Electrons
Orbital




Electrons, like light, exhibit both particle and wave-like
behavior!!!
Heisenberg Uncertainty Principle – it is impossible to
simultaneously measure both the location and velocity
of an electron.
Since we can’t know exactly where an electron is at any
specific time or how it travels, then we can only say where
it probably is. This 3-d region is known as an orbital.
Orbital – three-dimensional region around the nucleus
that indicates the probable location of an electron.
Can hold a maximum of two electrons.
Quantum Numbers
Address of an Electron
1. Principle Quantum Number (n)


Corresponds to the energy level (shell)
Relative cloud size
Is there a pattern?
8e2e-
18e-
The maximum number of electrons possible in an
energy level =
2n2
Practice Problems:
Calculate the maximum number of
electrons possible in the following:
n=2
#e- = 2(22) = 8
n=3
#e- = 2(32) = 18
n=7
#e- = 2(72) = 98
n=9
#e- = 2(92) = 162
2. Angular Momentum Quantum Number (l)


Corresponds to the sublevel.
Cloud shape
The maximum number of sublevels possible in an
energy level =
n
For instance:
The first level (n=1) can have 1 sublevel.
The second level (n=2) can have 2 sublevels. Etc…
**Only four sublevels have been identified.**
Symbols and Values for (l)

Values:
symbol
s
l = 0 to n-1
l value
0
Remember an orbital is the space
that can be occupied by a pair of
electrons!!
# of orbitals
1
# of e-
2
p
1
3
6
d
2
5
10
f
3
7
14
Shapes
Practice Problem
How many sublevels can the fourth
level (n=4) have?
4
Write the symbols and l values for the
four sublevels.
s
l=0
p
l=1
d
l=2
f
l=3
Review
Energy Level
(n)
Sublevels
# of Electrons
1
s
2
2
s, p
2+6 = 8
3
s, p, d
2+6+10 = 18
4
s, p, d, f
2+6+10+14 = 32
Magnetic Quantum Number (m)



Refers to the orbital
Orientation of the orbital in space (direction)
Orbital – the space that can be occupied by a
pair of electrons.
The values of m =
-l to +l
Assigning m values
The values of m =
-l to +l
symbol
l value
# of orbitals
m values
s
0
1
0
p
1
3
-1, 0,+1
d
2
5
f
3
7
-2,-1, 0,+1, +2
-3,-2,-1, 0,+1, +2, +3
Spin Quantum Number (s)




Refers to the spin of the electron
CW or CCW
Values of s may equal +1/2 or -1/2
Designated by arrows (
or
)



Pauli Exclusion Principle – no two electrons in an
atom can have the same set of four quantum
numbers.
Degenerate orbitals – orbitals of the same energy
(level & sublevel)
Hund’s Rule – shows a maximum number of two
electrons in a sublevel. (Electrons do not double up
in an orbital unless necessary!)
Summary of Quantum Numbers
Quantum Number Symbol
Represents
Information
Values
1. Principal
n
Level
Size of cloud
n = 1 to …
2. Angular
l
Sublevel
Shape of cloud
l = 0 to n-1
3. Magnetic
m
Orbital
Orientation
m = -l to +l
4. Spin
s
Spin
CW or CCW
s = +½ or -½