Electrons in Atoms
2.2 Configurations, Lewis Dot
Diagrams and the Electromagnetic
Spectrum
Electrons In Motion
• Electrons are negative and the nucleus is
positive
• Why aren’t electrons pulled into the nucleus
and held there?
• (1 min) Brainstorm answer with your shoulder
partner
• List as many ideas as possible
Niels Bohr(1885-1962
• Worked with Rutherford suggested:
– Electrons have enough energy to keep them in
constant motion
Bohr’s Explanation
• Electrons have energy of motion that enables
them to overcome the nucleus’s attractive
forces
• This explanation is called the planetary model
• Experiments show that electrons occupy
orbits with defined amounts of energy, not
random amounts like satellites in orbit.
The Electromagnetic Spectrum
• High voltage electricity can increase the
energy of an electron
• Electromagnetic radiation or radiant energy
can also supply energy to electrons
– Electromagnetic radiation travels in waves with
both electric and magnetic properties
• Example: Radiant energy from the sun
Properties of Waves
1. Frequency: number of wave vibrations per
second
– Unit of measure is hertz (Hz)
2. Wavelength: The distance between
corresponding points on two consecutive
waves
Relationship Between Frequency and
Wavelength
• A low frequency results in a long wavelength
Waves and Energy
• Waves transfer energy from one place to another
• Electromagnetic waves have similar
characteristics
• However, they can travel through empty space
– Ex. Radio waves
– Microwave radiation
– Visible light
• All of these forms of radiant energy are part of
the electromagnetic spectrum
Visible light
• Is a very small portion of the spectrum
Answer the Following:
1. What form of electromagnetic radiation in this diagram has the longest
wavelengths?
2. What wavelengths do microwaves have?
3. What is the unit of wavelengths?
4. What form of electromagnetic radiation in this diagram has the highest energy?
Answers
1.
2.
3.
4.
Radio Waves (10-100,000 nm)
0.010-1.0 nm
Nm (nanometers)
Gamma rays (10 19 -10 23 Hertz)
• Higher frequency has higher energy and
shorter wavelength
Aurora and Atomic Structure
• How does the aurora borealis relate to the
structure of an atom?
– Excited electrons dropping to lower energy levels
produces the different colored lights
– This supports the model of the atom having
electrons in specific energy levels
– The colors are predictable based on those
produced by electrons in specific gasses which
make up the atmosphere.
Electrons and Light
• What does the electromagnetic spectrum
have to do with electrons?
– It is related to the energy of motion of electrons
and radiant energy- different amounts of energy
released cause diff. colors
Analogy: Book Drop
• Rank the heights of the drop based on the
sound produced by the fall
• Close your eyes and listen carefully
• Which fell from the greatest height?
• Which fell from the lowest height?
• How could you tell?
• How does this relate to electron energy and
the light?
Emission Spectrum
• Emission Spectrum: the spectrum of light
released from excited atoms of an element
• Each element has its own, different, emission
spectrum
• It is like a fingerprint.
• Evidence of energy levels:
– Electrons absorb only enough energy needed to
move to a specific higher energy level
– When falling back they give off only the amount of
energy to drop them back to that lower energy:
giving off a specific color of light.
Electrons Moving to Different Energy
Levels
Electrons and Energy Levels
• Like your feet on a ladder, electrons can not
be between energy levels
• They must absorb the amount of energy
required to land on an energy level
However, energy levels are not evenly spaced
like rungs on a ladder.
• As n increases the energy levels get closer
together
Line Emission Spectra Lab
• Silently Read the lab Background information
• Note any questions that arise AS YOU READ.
– Mark the text
• Propose a question to investigate, during the
lab, by looking at various spectra
Your Hypothesis
• Construct a hypothesis
– An if then statement which connects the
independent variable (the one you change) to the
dependent variable (the one you can not change)
Example: If I lower the temperature of the room to
20 degrees for the next 24 hours, then all of my
plants will freeze.
If _____________________________________
then_____________________________.
Your Experiment
• How will you make your observations in order to
answer your question and test your hypothesis?
• Note the material available on the table.
• Write specific instructions in your “Experiment”
Section, be sure to say what you will do, what
you will write down and how you will record
your observations/data
• First……..
• Second…..
• Then……
Submit your plan for approval
• Once you have received approval, carefully
conduct your experiment.
• Prepare your poster presentation
• Be sure to include all of the required
components, from the lab handout.
• Share your poster, when assigned
Poster Presentations
The Electron Cloud
• Continuing research has shown that energy
levels are not neat
– They are regions of space around the nucleus in
which electrons are most likely to be found
The space around the nucleus where the atom’s
electrons are most likely to be found is called the
Electron Cloud
Electron In Energy Levels
• The lowest energy level is the smallest and
closest to the nucleus
– One S suborbital with one orbital =2electrons
• The 2nd energy level is larger, holds 8 electrons
– One S suborbital with one orbital =2electrons
– One P suborbital with 3 orbitals = 6 electrons
• The 3rd energy level is even larger and further
away from the nucleus, holds 18 electrons
– One S suborbital with one orbital =2electrons
– One P suborbital with 3 orbitals = 6 electrons
– One D suborbital with 5 orbitals = 10 electrons
Valence Electrons
• Electrons in the outermost or highest energy
level are called valence electrons
• Many physical and chemical properties of an
element are directly related to the number
and arrangement of valence electrons
• Valence electrons are the ones that interact
during a chemical reaction
Lewis Dot Diagrams
• Because valence electrons are very important
to the behavior of atoms, we represent them
is symbols
• Lewis Dot Diagrams represent VALENCE
electrons as dots around the chemical symbol
of the element
– Each dot represents 1 valence electron
Writing Lewis Dot Diagrams
• Helium
– Has 2 valence electrons, so 2 dots
He:
This is the Lewis Dot Diagram for Helium
You try one:
Write the Lewis Dot Diagram for Oxygen.
Assessment
• For each of the following elements, describe how many
electrons are in each energy level, and draw the Lewis Dot
Diagram
a)
b)
c)
d)
Argon
Magnesium
Nitrogen
Aluminum
1. Explain the change that occurs within an atom when it
emits light
2. Explain the differences and similarities between Bohr’s
model of the atom and the electron cloud model.
3. Describe how we concluded that electrons occupy specific
energy levels.
4. Use an everyday example to prove that light waves
transfer energy
Answers
Mg:
Al:
2,8,8
2,5
2,8,2
2,8,3
1. Electrons absorb energy and jump to higher energy levels.
Then electron drops down to lower level again, they give off
the energy as light.
2. Cloud- region of high probability of finding electron
Bohr- specific, neat orbits BOTH show e- in orbit
3. Atoms release energy of only certain frequencies, so certain
energy levels are given off, so electrons must be in only certain
frequencies
4.Photovaltaic cells, things in the light get warm, heat lights