Electrons, Energy, and Light Waves

When electrons are in the lowest possible energy levels, they are in their ground state

Electrons can absorb a quantum of energy and move to a higher energy level. This is called the excited state.

A quantum is a discrete amount of energy. Electrons can absorb a quantum of energy and move to a higher energy level. This is called the excited state. A quantum is a discrete amount of energy. It has to be the exact amount needed to send an electron to the next higher energy level.

The excited state is unstable, and electrons quickly return to the ground state. When electrons return to the ground state, they release some of the quantum of energy they absorbed. It is released as a photon of light.

The excited state is unstable, and electrons quickly return to the ground state. When electrons return to the ground state, they release some of the quantum of energy they absorbed. It is released as a photon of light.

Electrons can absorb a larger quantum of energy and move to an even higher energy level and a higher excited state.

Electrons can absorb a larger quantum of energy and move to an even higher energy level and a higher excited state.

The excited state is unstable, and electrons quickly return to the ground state. When electrons return to the ground state, they release some of the quantum of energy they absorbed. It is released as a photon of light.

The excited state is unstable, and electrons quickly return to the ground state. This electron absorbed a greater amount of energy, so it releases a photon of light with higher energy. It will be a different color than the first example because it has more energy.

Atomic Spectra (spectra is plural of spectrum) Bohr’s model finally explained the colors emitted by hydrogen glowing in a gas discharge tube Electrons can only make certain jumps, so the color of light emitted from the jump is always the same

All elements have unique atomic spectra (these are emission spectra) Kr Ne N

Properties of Light Light travels as a wave Light travels at “the speed of light” Light is electromagnetic radiation (EMR) Visible light is a very small part of the EMR spectrum (ROYGBIV) Of visible light, Violet light has the most energy Red light has the least energy increasing energy

Visible light is only a portion of the EMR spectrum

Speed of Light, c 'c' for 'constant' or the Latin celeritas for “swiftness” The speed of all light (EMR) is constant, and does not change!

Light is made of photons. A photon is a tiny “packet” of light energy Artistic conception of a photon by Jan-Henrik Andersen, professor of Industrial Design at University of Michigan, in collaboration with Fermilab physicists

A photon is both a particle and a wave…

Speed of light equals wavelength times frequency Units: m Units: 1/s or Hz

Energy of a photon equals the Planck constant times frequency Units: J

How is energy related to wavelength?

Light and Electrons Electrons can absorb varying sized quanta and go to varying excited states Each transition from excited state to ground state has a different amount of energy and a different wavelength of light Not all photons are in the visible light range Electrons can also act like waves

Electrons in specific energy levels have specific wavelengths 1 2 4 3 Ex.: Level 4 contains 4 complete wavelengths

What type of radiation is this? Practice #1 What is the wavelength of electromagnetic radiation having a frequency of 5.00 x 1012 Hz? What type of radiation is this? 6.00 x 10-5 m infrared

Practice #2 What is the frequency of electromagnetic radiation having a wavelength of 3.33 x 10-8 m? 9.01 x 1015 Hz

Practice #3 What is the energy of a photon of green light with a frequency of 5.80 x1014 1/s? 3.84 x 10-19 J

Recall: e- can transition between levels

Calculate energy of a transition Calculate the energy of the electron in both the initial (“before”) and final (“after”) locations

Practice #4 Calculate the energy associated with an electron transitioning from the second to the fourth energy level Is that energy being absorbed emitted? What is the corresponding wavelength of light?

The wavelength of a body with mass DeBroglie equation: v is velocity (not frequency, nu)

Practice #5 What is the wavelength in nanometers of an alpha particle (mass=6.64x10-27 kg) traveling at 3.0 x 107 m/s?

Practice #6 What is the wavelength in nanometers of a 1000 kg automobile traveling at 65 mi/hr?