Energy Unit

Energy of an Electron

The Wave-like Electron

Louis deBroglie

The electron propagates

through space as an energy

wave. To understand the

atom, one must understand

the behavior of

electromagnetic waves.

Wave-Particle DualityWave-Particle DualityJJ Thomson won the Nobel prize for describing the electron as a particle.His son, George Thomson won the Nobel prize

for describing the wave-like nature of the electron.

The electron is a particle!

The electron is an energy

wave!

Electromagnetic Radiation:

• Energy that moves through space and matter both in the form of magnetic and electric waves and in the form of a stream of particles.

Waves

• Waves are described by their amplitude, wavelength, crest, troughs and nodes.

• Amplitude = height of wave• Node = point where the wave crosses the line of equilibrium, (x-axis).• Trough = the lowest point of a wave.• Crest = the highest point of a wave.

Wave Characteristics• Wavelength

• The distance between two consecutive wave peaks.

• Frequency• How many wave peaks pass a certain

point per given time period.

Photons• Stream of tiny packets of energy…

LIGHT

SPEED of LIGHT• Light is described as being

particles of energy called photons which have wave characteristics but no mass.

• The speed of light is CONSTANT for the entire electromagnetic spectrum. All waves of the spectrum move at 299, 792, 458 m / s.

• Often the speed of light is rounded to 3.0 x 108 m/s.

• The variable used to represent the speed of light is “c.”

* Lower case “c” is used because it comes from the Latin word “celeritas” which means speed in Latin.

Electromagnetic radiation propagates through space as a wave moving at the speed of light.

LIGHT FORMULA• Light’s wavelength and frequency are inversely proportional.• As wavelength increases the frequency decreases.• As wavelength decreases the frequency increases. • The speed of light remains constant. • The equation for the relationship between the speed of light,

frequency and wavelength is . . .

Don’t let the change in variable confuse you! They mean the same.

1. What is the wavelength of a wave of green light with a frequency of 6.0x1014 S-1?

2. What is the frequency of a wave of violet light with a wavelength of 3.88x10-7 m?

The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation.

ENERGY OF Electromagnetic waves FORMULA

• The formula for calculating the energy of light is . . .

• E = Energy (joules)• h = Planck’s constant is 6.63 X 10 – 34 J*Sec.• f = frequency of the electromagnetic wave

1. What is the energy of a photon of light with a frequency of 5.0x1014 S-1?

Long Wavelength = Low Frequency = Low ENERGYShort Wavelength= High Frequency = High ENERGY

fireworks

• Fireworks use the emission of photons to display the fantastic colors.

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Different wavelengths of electromagnetic radiation carry different amounts of energy.• Red light carries less energy than blue light.

• The longer the wavelength of light, the lower the energy of its photons.

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Emission of Energy by AtomsAs the atoms release energy, we detect the photon of energy as specific colors of lightCopper emits green

light because it undergoes a different energy change.

Photon Emission• At an atomic level photons are associated with the absorption

of energy by electrons.• When electrons become excited through the absorption of

extra energy, the electrons jump to the next energy. • When the electrons move back to their original energy

level, they release the excess energy as a photon which can be seen as light with a specific color depending on the element.

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Remember that different wavelengths of light carry different amounts of energy per photon.

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Only certain types of photons are produced...we don’t see all colors only selected colors.

The energy is said to be emitted in

“discrete” amounts

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Atoms have certain discrete energy levels...energy levels are quantized...only certain values

are allowed.

More like fig. b

This produces bandsof light with definitewavelengths.

Electron transitionsinvolve jumps of definite amounts ofenergy.

…produces all of the colors in a continuous spectrum

Spectroscopic analysis of the visible spectrum…

…produces a “bright line” spectrum

Spectroscopic analysis of the hydrogen spectrum…

Element Spectra

Waves of The Electromagnetic SPECTRUM

• There are eight types of electromagnetic waves currently known to science. We will start with the waves that have the longest wavelengths and least energy, to end with the shortest wavelengths and most energy.

− Radio waves− Microwave − Infrared− Visible Light− Ultraviolet− X-rays− Gamma Rays− Cosmic Rays

Radio Waves• Radio waves have the longest wavelengths,

least frequency and least energy.• Radio waves have wavelengths ranging from 1

millimeter (0.039 in) to 100 kilometers (62 mi).• Radio waves have frequencies from 300 GHz

to as low as 3 kHz.

Radio waves• Radio waves are used

for transmitting information across wide areas.

• Radio waves transmit both audio and visual images.

• Television waves fall in the same range as radio waves.

MICROWAVES• Microwaves have shorter

wavelengths but more frequency and energy than radio waves.

• Microwaves can travel long distances.

• Microwaves are used for cooking are transmitted using a magnetron inside the microwave appliance.

• Microwaves in cell phones are transmitted using a transmitter chip and antenna.

MICROWAVES

• Cell phone frequencies are also microwaves.• The health risks associated with cell phone use is not a

myth.• The same microwaves which cook food and transmit cell

phone communication can also penetrate the skull.

infrared• Infrared is heat waves, heat energy.• Infrared makes up slightly more than half of

the sun’s energy that reaches earth.• Artificial infrared is used in incubation units

and buffet heat lamps.

infrared• Some animals such snakes as see

infrared.• Predator and graboids (Tremors) also

sees infrared.

White Light: Visible Light• White light is the combination of all the

wavelengths of visible light. White light comes from the sun and artificial light.

• When you see a white shirt, the shirt is NOT absorbing any colors they are ALL reflected so we see white.

• By sending white light through a prism it will break up into red, orange, yellow, green, blue, violet (ROYGBIV).

How we see color• Our eyes pick up the wavelengths of light that are reflected by an

object.• When we see a red shirt for example, the red shirt ABSORBES ALL the

wavelengths EXCEPT for red.• Red is reflected and that is what our eyes see.• When we look at green plants, the plants absorb ALL the colors

EXCEPT for green. The green wavelengths are REFLECTED so that is what we SEE.

Black is not a color!!

• There is a misconception that black is a color, some people think it is ALL the colors.

• That is NOT correct. White light is ALL the colors.• Black on the other hand is the ABSENSE OF COLOR. • Black is what happens when all the colors are absorbed and

NOTHING is reflected to the eye.• Our BRAIN fills the void with BLACK. • BLACK, in essence, is merely a figment of our imagination.

ultraviolet• Ultraviolet waves come from the sun and are pretty high energy. • Over exposure to ultraviolet results in freckles, suntans and skin

cancer. The high energy of ultraviolet creates irreparable DNA damage.

Ultraviolet•Ultraviolet can not be seen by the human eyes under normal conditions.•Occasionally children and young adults can see ultraviolet down to wavelengths of about 310 nm.•People with aphakia (missing lens) can also see some UV wavelengths.•Near-UV is visible to some insects such as bees and birds.

X-ray•X-ray waves have high energy and very short wavelengths used to look inside organisms and through layers of objects.•They pass through many materials opaque to light.•Prolonged x-ray exposure results in DNA damage leading to cancer and other illnesses.

X-ray• Marie Curie died of aplastic anemia

caused by overexposure to x-rays from her experimentation with radioactive elements.

Gamma ray• Gamma radiation, has extremely high frequency

and energy consisting of high-energy photons. • Gamma rays are ionizing radiation, and are thus

biologically hazardous.• Gamma rays come from regions of high

temperature such as solar flares.

Gamma ray• Gamma radiation is used in cancer therapy

because it destroys biomolecules.