Do Now: Take out completed Homework #2 AND text reading notes How many Principle Energy Levels are full in an atom of Tin (Sn)? Draw a Bohr diagram for Sodium (Na)

Who’s Ready for a Quiz? You Guys and Gals!

5.2 LET THERE BE LIGHT!

IV. Introduction to Light Visible Light (energy we see with): part of the Electromagnetic Spectrum

Waves Two Theories of Light Particles of Packets of Energy There was evidence for both models so the two theories were put together!!

Light: QUANTUM THEORY OF LIGHT A) packets or bundles of energy called PHOTONS or quanta B) travel in wave-like fashion C) produced when electrons drop from HIGH energy levels to LOW energy levels (the greater the drop, the greater the energy the light has)

1st an electron gains energy moves up in energy levels, then emits the energy & falls back to original energy level

Properties of Light Wavelength () distance between two equivalent points (peak to peak, or trough to trough) Frequency (F) –how often a peak or trough passes a point or an observer (units: Cycles/second OR Hertz) Energy (E) – amount of kinetic energy of the light with a certain  or frequency Speed (velocity) – same for all electromagnetic radiation 3 x108m/s

Lets Go to the HALL!

Relationships: Direct Indirect Indirect Frequency and Energy: Type _________________ F ______, E ________ or F ______, E ________ Frequency and Wavelength: Type_______________ F ______,  ________ or F ______,  ________ Wavelength and Energy: Type _________________  ______, E ________ or  ______, E ________ Indirect Indirect

3. The Rainbow: A Continuous Spectrum

3. The Rainbow: A Continuous Spectrum R O Y G B I V Long  Short  Low F High F Low E High E LONG STEM RED ROSES: All “L’s” go together with RED

LONG STEM RED ROSES: All “L’s” go together with RED Low _____________ RED Wavelength Frequency Energy

Continuous Spectrum When radiation from the sunlight passes through a prism: a rainbow – a spectrum of colors – is seen the colors are not separated from one another but blend together due to the overlap of the line spectra of the 67 different elements in the sun

Bright Line Spectrum When radiation from an excited atom (element) passes through a prism, the radiation is separated into various wavelengths and colors Colors are not blended – spectrum is discontinuous – and you observe lines of color at different locations

Our spectroscopes Use a diffraction grating instead of a prism Diffraction grating is piece of plastic with lines etched in it. Breaks up the light the same way as a prism

Bright Line Spectra and the Bohr Atom An electron must absorb energy before it can give off colors we see in the bright line spectra. When energy is added, the electron moves to a higher energy level. The potential energy of the electron increases. This is an unstable situation.

Bright Line Spectra and the Bohr Atom In order for the electron to return to a lower and more stable energy level, the added energy must be given off. When the electrons return to the lower energy levels this decreases the PE because the added energy is given off  

Bright Line Spectra and the Bohr Atom The colors of the bright line spectra are seen. Moving electrons to different energy levels requires different amounts of energy. These different amounts of energy produce the different colors.

Bright Line Spectra and the Bohr Atom

Illustrate the process by which light is emitted

Bright Line Spectra and the Bohr Atom Movement of an electron between the same 2 energy levels in DIFFERENT elements will produce different colors. The energy between the energy levels depends on the number of protons and the number of electrons that each element has.

Bright Line Spectra (BLS) BRIGHT LINE SPECTRA are produced when “electrons in the EXCITED STATE” fall back to lower energy levels of the GROUND STATE. Unlike the continuous spectrum of sunlight, only certain colors will be present in the BRIGHT LINE SPECTRA.

Bright Line Spectra (BLS) The BRIGHT LINE SPECTRUM is like a “fingerprint” of the element that produced the spectrum.

Bright Line Spectra (BLS) Like a fingerprint the BRIGHT LINE SPECTRA can be used to identify the element. When viewed with a spectroscope, the individual bands of colors in the BRIGHT LINE SPECTRUM can be seen and the wavelength of each band determined. By matching to a chart of BLS, the identity can be determined

Bright Line Spectra (BLS)

Match the lines to ID the Mystery Elements

Guided Practice p 9 1) What is the identity of unknown element? Element Y 2) Which of the two elements above are present in the BRIGHT LINE SPECTRUM? Element X and Element Y

Ground and Excited States The lowest possible energy state that an electron can occupy is called the Ground State. This is a very stable condition. The principle energy levels, which are occupied match those predicted by the electron configuration on the periodic table.

Ground and Excited States When electrons gain energy, the electrons move to higher principle energy levels then they would normally occupy. This unstable situation is called the EXCITED STATE. The electrons will release the absorbed energy, often seen as the bright line spectrum of the element, and fall back to the ground state.

How to tell when energy will be absorbed or released The Principle Energy Level (n) changes: If the number of the principle energy level (n) goes up, then energy is added or absorbed (ENDO) n = 1 to n = 3 OR n = 3 to n = 4

How to tell when energy will be absorbed or released The Principle Energy Level (n) changes: If the number of the principle energy level (n) goes down, then energy released or emitted (exo) n = 2 to n = 1 OR n = 5 to n = 3

If the energy is emitted.. Then photons (colors) are seen

1) n = 1 to n = 2 ______________ +E 2) n = 4 to n = 3 ______________ Determine if energy is added/absorbed (+E) or released/emitted (-E) for the following transitions: 1) n = 1 to n = 2 ______________ +E 2) n = 4 to n = 3 ______________ -E 3) n = 2 to n = 1 ______________

6) n = 1 to n = 5 ______________ +E 7) n = 4 to n = 2 ______________ Determine if energy is added/absorbed (+E) or released/emitted (-E) for the following transitions: 6) n = 1 to n = 5 ______________ +E 7) n = 4 to n = 2 ______________ -E 8) n = 2 to n = 3 ______________

Which ones produced color? Which of those transitions would you see BLS- colors produced?

II) How do you tell the excited and ground state apart from the electron configuration??

Look up on the PT Ground State: Matched the predicted electron configuration found on the periodic table. In other words, it follows the order given 2-4   Ground!!!

Ground State

Look up on the PT Ground State for Oxygen (O) on PT= 2 – 6 (8 total electrons) Possible Excited State for Oxygen = 1 – 7 (still 8 total electrons) The first energy level is not filled before moving into the second energy level.

Excited State

Key to determining The KEY here is that the configuration does not MATCH the one on the PT. Another possible excited state for oxygen: 2 – 5 – 1 (still 8 total electrons) What could be another excited state for oxygen?

What is a possible excited state for fluorine (F)? Be careful! Number of electrons must equal the atomic number for F!

G 2 2 E 3 G Guided Practice p 11 C 2-4 F 1-8 Cl 2-8-7 For the following elements, fill in the chart and determine if the electron configuration is in the GROUND STATE (GS) or EXCITED STATE (ES). Element Symbol Electron Configuration Principle Energy Levels Ground or excited state? C 2-4 F 1-8 Cl 2-8-7 G 2 2 E 3 G

E 4 3 E Guided Practice p 11 B Na 2-7-2 2-1-1-1 Element Symbol Electron Configuration Principle Energy Levels Ground or excited state? B 2-1-1-1 Na 2-7-2 E 4 3 E

2 G 3 E 4 G Guided Practice p 11 O 2-6 S 1-8-7 Zn 2-8-18-2 Element Symbol Electron Configuration Principle Energy Levels Ground or excited state? O 2-6 S 1-8-7 Zn 2-8-18-2 2 G 3 E 4 G

6 E G 4 Guided Practice p 11 Br 2-8-18-7 1-7-17-8-1-1 Element Symbol Electron Configuration Principle Energy Levels Ground or excited state? Br 1-7-17-8-1-1 2-8-18-7 6 E G 4

Things to do RIGHT NOW Work on the homework Work on the Vocabulary Assignment DO IT NOW!