Electrons!!!
They light up my life!
Remember Rutherford?
He figured out that:
Atoms are mostly empty space
Atoms have a very small, dense, positively charged
nucleus.
These things were very nice to know; however they
didn’t explain how atoms behaved in chemical
reactions.
But he had a student by the name of Neils Bohr who
was more of a physicist than chemist.
Bohr-ing discoveries
So Bohr looked at electrons to see why
atoms behave as they do:
He figured out that:
Electrons occupy energy levels, like
rungs on a ladder.
Electrons aren’t found between levels.
In other words, electrons are quantized
and only have certain amounts of
energy.
These quanta of energy are
released as packets of light energy
called photons
Energy levels are not evenly spaced
However, Bohr’s theories only
explained a hydrogen atom.
More Bohr
You’re probably (or hopefully) wondering: “How did
Bohr figure out this energy level/ladder stuff?”
Bohr knew about the electromagnetic (EM) spectrum
Bohr and the EM
Spectrum
When Bohr heated up some hydrogen gas it produced this
spectrum
What does this spectrum for hydrogen tell you?
Hint: There are individual lines, not a continuous
spectrum.
The Entire Spectrum for
Hydrogen
Other scientists discovered
the other spectral lines for
Hydrogen, as seen here:
The Lyman series are the
electron drops that produce
ultraviolet radiation.
The Bahmer series produces
visible light.
The Paschen series produces
infrared light
Electron energy
The amount of energy an electron absorbs or
releases can be determined by an equation derived
by Max Planck.
Energy = Planck’s constant x frequency
E = hv
Planck’s constant = 6.6262 x 10-34 Joule-seconds
A Joule is a measurement of energy.
There are 4.2 kilojoules of energy in one food calorie.
Some energy problems
Suppose an electron produces light with a frequency of 5 x 1014
Hz, how much energy is being released by the electron falling?
E = hv
E = 6.6262 x 10-34 J-sec x 5 x 1014 Hz = 3.3131 x 10-19 Joules
With sig figs, that would be 3 x 10-19 Joules
Suppose an electron produces light with a frequency of 7.5 x 1014
Hz, how much energy is being released by the electron falling?
E = hv
E = 6.6262 x 10-34 J-sec x 7.5 x 1014 Hz = 4.96965 x 10-19 Joules
With sig figs, that would be 5.0 x 10-19 Joules
A more complicated
math problem
Suppose an electron produces light with a wavelength of 700 nm
(700 x 10-9 meters). How much energy is being released?
Since you have wavelength, you need to change to frequency first.
Remember c = λv, or v = c/λ
So v = (300,000,000 m/s)/(700 x 10-9 meters) = 4 x 1014 Hz
E = hv
E = 6.6262 x 10-34 J-sec x 4 x 1014 Hz = 2.65048 x 10-19 Joules
With sig figs, that would be 3 x 10-19 Joules
Heisenberg and
Shrodinger
These two figured out that the electrons were found
in areas of probability instead of in planetary like
orbits (as Bohr proposed).
The reason the electrons must be in areas of
probability is because they are…they are… they
are... particles and waves at the same time!?!
So Bohr’s energy levels are still okay, but the
electrons are in areas of probability (orbitals).
The Quantum
Mechanical Model
Our current model of the atom is the quantum mechanical
model. It includes the following propositions:
Electrons are quantized: They have discreet amounts (1 or
2 or 3, but not between 1 or 2 or 3) of energy since they are
only found at certain energy levels.
Electrons behave as waves and, therefore, are found in
areas of probability called orbitals
Orbitals are areas where electrons are likely to be found.
Electrons and where they live
As Bohr said, electrons can be found on different energy levels, or
at different distances from the nucleus.
These energy levels are numbered 1,2, 3, etc. (Floors in an
apartment building)
The energy levels also have sublevels (Apartments in an apartment
building)
An energy level has the same number of sublevels: Level 1 has 1
sublevel, level 2 has 2 and so on.
The sublevels are as follows: s, p, d, f. Each sublevel makes a block on
the periodic table
And each sublevel has orbitals (Rooms in the apartments). Each
orbital holds 2 electrons.
S sublevel has 1 orbital, so it holds 2 electrons
P sublevel has 3 orbitals, so it holds 6 electrons
D sublevel has 5 orbitals, so it holds 10 electrons
F sublevel has 7 orbitals, so it holds 14 electrons
Orbitals
And each sublevel has orbitals (Rooms in the
apartments). Each orbital holds 2 electrons.
S sublevel has 1 orbital, so it holds 2 electrons
P sublevel has 3 orbitals, so it holds 6 electrons
D sublevel has 5 orbitals, so it holds 10 electrons
F sublevel has 7 orbitals, so it holds 14 electrons
Some rules for figuring out
electron configurations
Aufbau Principle: Electrons fill the lowest energy
levels first.
Pauli Exclusion Principle: Up to 2 electrons can fill an
orbital and the electrons must have opposite spins.
Hund’s Rule: Each orbital of an energy sublevel gets
one electron before putting a second electron in an
orbital of the energy sublevel.
How to figure out an electron
configuration: Periodic Table Edition
Just fill in things as you go…
Label the blocks on your periodic table.
Energy level is the period.
Except on d block you subtract 1 from the period to get
the energy level
In f block you subtract 2from the period to get the energy
level (I’ll never have you do an f block element on a test.
The number over in the block is how many electrons the
element has in that sublevel.
Let’s do some electron
configuratin’!!!
Oxygen
Aluminum
Sodium
Chromium
Strontium
Bromine
Iron
Uranium
Energy Levels
This is how I recheck my work.
Wave stuff
The three most important characteristics of waves for you to
know are:
Wavelength:
How far it is between crests of waves
Measured with units of length like meters or nanometers
Frequency:
How often waves pass by.
Measured in Hertz (Hz) or megahertz, or kilohertz
Wavelength and frequency are inversely proportional.
The product of wavelength and frequency equals a constant
Constant = wavelength (λ) x frequency (Υ) c = λΥ
The longer the wavelength the lower the frequency
The shorter the wavelength the higher the frequency
Waves and Energy
If you look at the electromagnetic spectrum, what
can you tell me about the relationship between
wavelength and energy?
Shorter wavelength = higher energy
What about the relationship between frequency and
energy?
Higher frequency = higher energy
Waves, energy, light and electrons
Hopefully you remember that when you “excite” an
electron, it jumps and then releases light as it falls
back down…
If I can see the light
I can tell the frequency
I can tell how much energy was released
So I can tell how far the electron jumped