BELLRINGER – 2 MINS TO HAND IN

How does the wavelength of a light beam and the size of a slit it is going through control the amount of diffraction?

DO WORK STOP

BELLRINGER

UPDATES SLC

Expect more e-mails/phone calls if you’re not showing up

Physics Club

Missing Lens

OBJECTIVES Learn what spectrometry is and how

scientists use it to identify specific atoms.

Be able to calculate the photons released from different energy level drops.

HOMEWORK Let’s go over it.

A LOOK INTO OUR UNIVERSE

What can electromagnetic waves tell us about stars, planets, and

galaxies?

SPECTROSCOPY Spectroscopy is the process of obtaining a

spectrum and reading the information it contains.

Each element has its own unique spectra.

If we collect the spectra of distant objects in our universe we can figure out what elements they are made of.

HOW DOES IT WORK? To perform spectroscopy you need a spectrometer

A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum

For visible light we will use a spectrometer that has a prism in it and we will use our eyes as the detector. Different examples of spectrometers

HOW DO WE DISPLAY THIS SPECTRA? Two ways 1. Draw what you see 2. Plot an Intensity vs.

Wavelength Graph

THREE BASIC TYPES OF SPECTRA Continuous Spectrum

Spectrum of an ordinary light bulb; rainbow because it has all the visible wavelengths in it

Emission Line Spectrum A thin cloud of gas emits light only at specific

wavelengths that depend on its composition and temperature

Absorption Line Spectrum If a cloud of gas is between us and a white light source,

we still see most of the continuous light emitted by the light. However, the cloud absorbs light of specific wavelength and leaves dark lines

THREE BASIC TYPES OF SPECTRA

THREE BASIC TYPES OF SPECTRA

CHECKPOINT1. What can a spectrometer tell us about

a very distant object?

2. What are the three types of spectra?

HOW ARE THE ENERGY LEVELS DETERMINED? In 1913 Niels Bohr proposed that an

atom has a positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus – similar to the structure of a solar system, but with the attraction provided by electrostatic forces rather than gravity.

BOHR MODEL

EXCITED BOHR MODEL Bohr said that when energy is added to

an atom it becomes excited and the electrons can temporarily move up to higher orbits.

BOHR MODEL PHOTONS The Bohr Model says that as an electron

returns to its normal orbit it releases the energy it previously absorbed in the form of a photon.

CONSERVATION OF ENERGY

WHERE DO EMISSION LINES COME FROM? When incoming energy excites a

hydrogen atom, its electron is moved into a higher energy level.

Atoms do not want to stay in higher energy levels

So as the electron returns to its original energy level it releases the energy that originally excited it as a photon (light particle)

BYE BYE BOHR The Bohr model has been superseded by

quantum mechanics.

Electrons do not stay in perfect little orbits, nor are they held there by the electrostatic force.

Quantum mechanics says that electrons are in “electron clouds” that show the probability of an electron being there.

ELECTRON CLOUDS

ELECTRON CLOUDS

CHECKPOINT1. What does an electron do as it absorbs

energy?2. What happens when an electron drops

an energy level?

BELLRINGER

UPDATES SLC

Expect more e-mails/phone calls if you’re not showing up

Physics Club

Missing Lens

OBJECTIVES Learn what spectrometry is and how

scientists use it to identify specific atoms.

Be able to calculate the photons released from different energy level drops.

PHOTONS FROM ATOMS A specific photon is emitted during any

energy level transition as long as the electron is dropping down at least one energy level.

To figure out the energy between any transition use:

PHOTONS FROM ATOMS This photon has a specific frequency

that corresponds to the energy released from the atom

Remember:

We organize energy levels on “Energy Level Diagrams”

NUMBER OF POSSIBLE PHOTONS

HOW DO WE USE SPECTRA TO FIGURE OUT WHAT SOMETHING IS? Emission and absorption lines form as a

direct consequence of the fact that each type of atom, ion, or molecule possesses a unique set of energy levels.

We know the energy levels of atoms, ions, and molecules so we just need to match our experimental observations with what we already know.

ENERGY LEVEL DIAGRAM OF HYDROGEN

1electronvolt (eV) = 1.60x10^-19 J(Reference Table)

When an atom ionizes it loses all of its electrons

WHY ARE THE ENERGY LEVELS NEGATIVE NUMBERS? The negative eV value describes the difference

in energy between an electron in an energy level and an electron infinitely far from the nucleus

Where Z is the atomic number n is the energy level (1, 2, 3,….)

This only works as an approximation for a single electron (need quantum mechanics)

PRACTICE TOGETHER What is the energy of the photon

emitted from a hydrogen atom when the electron falls from level 3 to 1?

Is this different than if it fell from level 3 to 2 and then 2 to 1?

PRACTICE CONT’D n=3 to n=1; n=3:-1.51eV n=1:-13.60eV

𝐸 h𝑝 𝑜𝑡𝑜𝑛=−1.51𝑒𝑉 −(−13.60𝑒𝑉 )𝐸 h𝑝 𝑜𝑡𝑜𝑛=12.09𝑒𝑉

PRACTICE CONT’D n=3 to n=2 n=3:-1.51eV n=2:-3.40eV

n=2 to n=1 n=2:-3.40eV n=1:-13.60eV

𝐸 h𝑝 𝑜𝑡𝑜𝑛=−3.40𝑒𝑉 −(−13.60𝑒𝑉 )𝐸 h𝑝 𝑜𝑡𝑜𝑛=10.20𝑒𝑉

PRACTICE CONT’D What frequencies do the three different

photons have?

PRACTICE CONT’D

Would we be able to see all three photons with our eyes?

No, only the photon released from energy level 3 to 2 falls within the visible spectrum of the EM radiation.

TEXTBOOK PRACTICE Page 772 answer questions 29, 30, 32,

33

29. 3.91eV; this energy corresponds to level E6

30. 1.91eV31. Skip it.32. A) 2.72eV B) 3.06eV33. 1.24eV; 2.99x10^14Hz

HOMEWORK Regents Part 2

June 2014Due Friday: Even if you miss class

SPECTROMETERS Using a spectrometer with LEDs demo

Why aren’t the colors in very thin circles?

What can a spectrometer tell you about how a fluorescent light works?

BELLRINGER

UPDATES Missing Lens

Homework due Friday

No Physics Club todayTomorrow

SLC Thursday

ASTRONOMY LAB We will use 5 samples

Draw what you see Compare it to a known spectrum

ASTRONOMER LAB Record spectra on a separate sheet of

graph paper. Your scale should range from 400nm to 700nm.

Use the whole width of the paper.

400nm

450nm 500n

m

550nm 600n

m

650nm 700n

m