Download Chapter 6 * Electronic Structure of Atoms

Chapter 6 – Electronic Structure
of Atoms
Electromagnetic Spectrum (Light)
We can use wavelength and frequency to calculate the
energy in a photon (particle of light).
low frequency
high frequency
Wavelength (l) is the distance between two crests on a
wave.
Frequency (f) is the number of waves that pass through a
particular point in 1 second (Hz = 1 cycle/s).
What is the relationship between energy
and frequency?
Energy Increases
Frequency Increases
Energy and frequency are directly related
If frequency increases
If energy decreases
then energy increases
then frequency decreases
What is the relationship between energy
and wavelength?
Energy Increases
Wavelength Decreases
Energy and wavelength are inversely related
If wavelength increases
then energy decreases
If wavelength decreases
then energy increases
What is the relationship between frequency
and wavelength?
Frequency Increases
Wavelength Decreases
Energy and wavelength are inversely related
If frequency increases
then wavelength decreases
If frequency decreases
then wavelength increases
Why do we care about light in Chemistry?!
Electrons release light when they are excited
and then calm back down.
eLight (Photon – particle of light)
Examples of light are gamma rays,
x-rays, radio waves, microwaves
The particle of light released is called a photon
Properties of Light
• All electromagnetic radiation travels at the same
velocity: Namely the speed of light in a vacuum (c) is
3.00  108 m/s.
c = l
Ex: A certain AM radio station broadcasts at a frequency
of 6.00x102 kHz. What is the wavelength?
Properties of Light
Light can be defined as both a
PARTICLE and a WAVE.
Properties of Light
• Energy (light) is emitted or absorbed in discrete units
(quantum)
• Each metal has a different energy at when it emits
electrons. At lower energy, electrons are not emitted.
• Einstein used quanta to explain the photoelectric
effect. Energy is proportional to frequency.
E = h
where h is Planck’s constant, h = 6.63  10−34 J∙s.
Properties of Light
Ex: A given light has energy of 2.85x10-19 J.
Calculate the frequency and wavelength of
that light.
The Bohr Model
1. Electrons can have specific (quantized) energy values.
2. Light is emitted as e- moves from one energy to a lower
energy level
3. Energy is depicted in the following equation:
E = RH ( 1n 2 –
i
1
nf2
)
where RH is the Rydberg constant, 2.18  10-18 J, and ni and nf are
the initial and final energy levels of the electron.
Energy Practice
Ex: A photon has absorbed energy when it
jumped from n = 2 to n = 4 level. Calculate:
a) Energy
b) Frequency
c) Wavelength of the photon
Electron Configurations
As chemists, we need to know
where an electron is at so we
can manipulate it and design
awesome stuff
Image of iron atoms
on copper surface
Moving away from the Bohr Model…
If negative electrons actually orbited a positive nucleus, they would
eventually spiral in and collide, causing an explosion.
In reality, the position of an electron is
a matter of probability.
The space where an electron will
probably be found is called an
“orbital”
Probably here
Probably NOT here
Quantum Numbers
• Four quantum numbers are required to
describe the distribution of electrons in
atoms.
• Each orbital describes a spatial distribution
of electron density.
Principal Quantum Number (n)
• The principal quantum number, n, describes
the energy level of the orbital
• The values of n = 1,2,3,4…
• It gives you the distance of e- from the nucleus
Angular Momentum Quantum Number (l)
• This quantum number gives the shape of the
“volume” of space that the e- occupies
• l = 0,1,2,3 … n-1
Magnetic Quantum Number (ml)
• The magnetic quantum number describes the
orientation of the orbital in space.
• ml = −l, … 0, … +l
• If l = 1 (p orbital), then ml = -1, 0, or 1
• If l = 2 (d orbital), then ml = -2,-1, 0, 1, or 2
• If l = 3 (f orbital), then ml = -3,-2,-1,0,1, 2, or 3
Relation to Quantum Numbers and Orbitals
Magnetic Spin Quantum Number (ms)
• Spin quantum number displays the orientation
of the electron within the orbital
• There can only be 2 electrons in an orbital,
where the ms value is either -1/2 or +1/2
+1/2
-1/2
Subshell Shapes
These shapes
represent
where the
electrons are
probably
hanging out
The Four Subshells
Subshell
s
Shape
Sphere
Max # of
electrons
# of
orbitals
2
1
The Four Subshells
Subshell
p
Shape
Dumbbell
Max # of
electrons
# of
orbitals
6
3
The Four Subshells
Subshell
d
Shape
4-Lobed
Max # of
# of
electrons orbitals
10
5
The Four Subshells
Subshell
f
Shape
6-8 Lobed
Max # of
electrons
14
# of
orbitals
7
Now for a couple rules:
Aufbau Principle: add electrons from lowest
energy to highest energy (you pretty much already
do this when you use the proper filling order)
Pauli Exclusion Principle: There is a maximum of
two electrons for each line (or orbital)
Hund’s Rule: Electrons fill in each orbital first
before they start pairing up with an electron
Using the periodic table makes it sooooo easy! All you
have to do is memorize this:
This is what the periodic table would
look like if we had more room
Or…you can memorize this:
What is an electron configuration?
It identifies what and where we can expect to find an
atom’s electrons
The electron configuration for Hydrogen
1
1s
Shell (could be 1-7)
Subshell
(s,p,d,f)
Number of e- in subshell
s: max of 2
p: max of 6
d: max of 10
f: max of 14
Warm Up
1. What are the 3 orbitals and how many
electrons can each orbital hold?
2. What is the next orbital in the series of filling
up of the electrons?
1s, 2s, 2p, 3s,3p,__
3. Given the electron configuration of 1s2 2s2
2p5
What is the element?
Writing the
e
configuration:
Steps:
1. Count the number of electrons in the element
2. Use the periodic table to follow the order of filling
3. As you start writing keep count of the electrons used
 Remember: s [2e-]
p [6e-]
d [10e-]
f [14e-]
4. Check the number of electrons when finished
Examples:
1) Carbon [6e-]
2) Sodium [11e-]
1s2 2s2 2p2
1s2 2s2 2p6 3s1
Use the nearest noble gas as a short cut. [He,
Ne, Ar, Kr, Xe…]
Longhand Configuration
Sulfur
16e
2
1s
2
2s
6
2p
2
3s
Shorthand Configuration
Sulfur
16e
2
4
[Ne] 3s 3p
4
3p
Orbital Diagrams
• Each box in the diagram
represents one orbital.
• The arrows represent the
electrons, where each
arrow indicates the spin