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 Waves1. 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. Radio Waves (10-100,000 nm)2. 0.010-1.0 nm3. Nm (nanometers)4. Gamma rays (10 19 -10 23 Hertz)

• Higher frequency has higher energy and shorter wavelength

Aurora Borealis : Northern LightsWhat causes these lights?• Caused by Solar Winds: A continuous flow of electrons

and protons from the sun• High-energy charged particles collide with oxygen and

nitrogen in the ionosphere transferring energy to them• The increased energy causes the electrons to jump to

higher energy levels• When the electrons return to the lower energy level

they release the energy as light• The amount and location of the energy released

determines the visible color

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 Diagrama) Argonb) Magnesiumc) Nitrogend) Aluminum

1. Explain the change that occurs within an atom when it emits light2. 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

2,8,8 2,5 Mg: 2,8,2 Al: 2,8,31. 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 orbit3. Atoms release energy of only certain frequencies, so certain energy levels are given off, so electrons must be in only certain frequencies4.Photovaltaic cells, things in the light get warm, heat lights