5 Minutes to Finish Sheets – prepare a 15 to 30 sec blurb Class Avg % A’s % B’s % C’s % F’s 2nd 76 27 9 36 3rd 85 42 43 5 10 4th 74 16 32 5th 73 25 20 45 6th 17 All 76.8 22.4 27.2 21.6 28.6

The Electromagnetic Spectrum The electromagnetic spectrum is a series of waves that have different wavelengths.

Visible Spectrum The visible spectrum is continuous (there are no breaks and the colors blend together). White light is a combination of ALL colors of light. A prism breaks up white light into the separate colors so we can see them. Each color has a definite frequency and wavelength. The speed of these colors never changes – always speed of light (c)

Visible spectrum- Frequency & Wavelength low energy colors high energy colors Red Orange Yellow Green Blue Indigo Violet

EM spectrum in real life! UV Light Television FM Radio Infrared Waves Microwaves & Radar AM Radio Visible Light Telemetry Millimeter waves Shortwave Radio X-rays and Gamma rays

Radio waves/TV/Short Wave are used in “classic” televisions and in radio. Radar wave are what we know as the old “doppler” waves. These images are used from things such as weather or in the military. Infrared Waves detect heat. These waves are used in night vision goggles. UV waves are used in tanning beds, to kill bacteria, and irradiate food. X-rays are used to see inside the body. Waves can penetrate through the skin, but bounce off the more dense bone producing a reflection on the x-ray. Gamma Rays are used in radiation therapy and gamma-surgery

Wave Model Light consists of electromagnetic waves that travel at 3.00 x 108 m/s That’s 670 616 629 miles per hour! That’s like 1200 lunar orbits around the earth a day!

Wavelength and Frequency All EM waves move at the speed of light. c = fλ c = speed of light = 3.00 x 108 m/s f = frequency (Hz) λ = lambda = wavelength (m) As wavelength increases, frequency __________.

EM Waves Frequency – number of cycles that pass a given point in a given amount of time. Measured in Hertz (Hz) 1 Hz = 1 wave passes per second 400 Hz = 400 waves pass per second ½ Hz = ½ wave passes per second

Practice Problems c = f λ If an EM wave has a wavelength of 630 nanometers, what is its frequency? (1 nm = 10-9 m) If an EM wave has a frequency of 548 Hz, what is its wavelength? c = 3.00 x 108 m/s f = 548 Hz λ = ? c = 3.00 x 108 m/s f = ? λ = 6.30 x 10-7 m c = f λ 3.00x108 m/s=(548 Hz)λ c = fλ 3.00x108 m/s=f(6.30x10-7 m) λ = 547445 m f =4.76 x 1014 Hz

Practice problem λ = 6.85 x 10-6 m Find the wavelength of light with a frequency of 4.38 x 107 MHz. c = 3.00 x 108 m/s f = 4.38 x 107 MHz λ = ? c = fλ 3.00 x 108 m/s = (4.38 x 1013 Hz)(λ) λ = 6.85 x 10-6 m

Particle Model The idea that light can act as a particle. These particles are called photons, or quanta, and can move other matter.

Photoelectric Effect The particle model was needed to explain why when you shine a high energy light on metal, electrons are ejected (moved) from the metal. This powers solar-powered calculators.

Einstein Einstein proposed in 1905 that light can behave as both a wave and a particle. He defined a photon is a particle of electromagnetic radiation with no mass and carries a quantum of energy.

The energy contained in a photon (a quantum) depends on its frequency. E = hf E = energy (units are in Joules) h = Planck’s constant = 6.63 x 10-34 J.s f = frequency (Hz)

Practice Problem E = hf If a wave has a frequency of 230 Hz, what is the amount of energy of one photon (quantum) of this wave?

Practice Problem E = hf If a wave has a frequency of 230 Hz, what is the amount of energy of one photon (quantum) of this wave? E = hf E = (6.626 x 10-34 Js)(230 Hz) E = 1.5 x 10-31 J

Practice Problem E = hf, c = fλ If a wave has a wavelength of 400. nm, what is the amount of energy of one photon (quantum) of this wave?

Practice Problem E = hf, c = fλ If a wave has a wavelength of 400. nm, what is the amount of energy of one photon (quantum) of this wave? 400. nm = 4.00 x 10-7m f = c/λ E=hf So, E = hc/λ = [(6.626 x 10-34Js)(3.00x108m/s)]/(4.00x10-7m)

Relating electrons to light Remember that electrons occupy energy levels - the region surrounding the nucleus where an electron is likely to be found (think of rungs on a ladder, fixed levels with space in between) When electrons are in their lowest energy level, they are said to be in their “ground state” It is possible for electrons to jump from ground state to a higher energy level (called excited state) by absorbing energy.

Relating electrons to light When electrons gain energy somehow, they can then occupy a HIGHER ENERGY LEVEL. They jump up to the next level and are said to be in their “excited state”. When electrons lose energy they will fall back down to their GROUND STATE and release energy, and some of it is released as waves we can see – LIGHT!

Relating electrons to light The electron configuration of sodium at ground state is 1s22s22p63s1. The electron configuration of sodium at an excited state is 1s22s22p53s2.   What happened?

Practice Write the electron configuration of the following elements in their ground and excited states: Element Sodium Fluorine Oxygen Ground state electron configuration Ion electron configuration Excited state electron configuration

Atomic Emission Spectrum Continuous Spectrum (no breaks)

EM Spectroscopy The use of a spectroscope to observe this EM radiation is called EM spectroscopy. This EM radiation can be classified as either an absorption spectra or emission spectra.

Atomic Emission Spectrum

Absorption Spectra “Dark line spectra” Electrons can jump to a higher energy level, but the atom must absorb energy in order to reach this excited state

Absorption spectra are different for each element Hydrogen Sodium

Emission Spectra “Bright line spectra” When electrons leave the excited state and return to the ground state, they emit energy

Emission spectra are different for each element Hydrogen Iron

How do we use the absorption and emission spectra? Each element gives off unique bright line and dark line spectra Can be used to determine the composition of stars, comets, and planets by analyzing the received light Can be used to determine the concentration of chemical compounds in a sample Reports of its use in differentiating malignant tumors from benign.