Unit 6: Electrons in Atoms

part 1: properties of waves

Frequency• Definition number of waves that pass

a given point per unit of time• Symbol (Greek letter nu)• Units Hertz (abbreviated Hz)

– 1 Hz = 1 wave/second – 1Hz = 1/s

frequency

Wavelength

• Definition distance between similar points in a set of waves

• Symbol (Greek letter lambda)• Units meters (base unit)

wavelength

Amplitude

• Definition distance from crest or trough to the normal (baseline)

• Units meters (base unit)

amplitude

Low

Medium

high

Normal (baseline)

energy

• Waves do not have energy, they transmit energy

• Definition the ability to do work• Symbol E• Units Joules, abbreviate J

Speed

• Definition distance that an object moves per unit of time

• Symbol c• Units m/s

Electromagnetic (EM) waves

• travel in a vacuum (not a vacuum cleaner…vacuum means “space that is empty of matter”); they do NOT need a medium (like air or water) to travel through

• travel at the speed of light

Electromagnetic Spectrum

• the range of all possible frequencies of electromagnetic radiation

Red Martians Invaded Venus Using X-ray Guns

Radio

Micro

Infrared

Visible

Ultraviolet

X-ray

Gamma

Visible light

• ranges in wavelength from approximately 400 nm (4 x 10-7 m) to 700 nm (7 x 10-7 m).

• Acts as a wave and a particle (photon)• Each color has a unique wavelength, energy,

and frequency range• Makes the colors of the rainbow ROY G BIV

Which has more energy, red light or blue light?

Which has more energy, yellow light or red light?

How is energy related to the wavelength?http://williamcraigcook.com/fireworks/DiffColors.jpg

Relationships

• Energy and Amplitude – direct

low energy high energylow amplitude high amplitude

Relationships

• Frequency () and Wavelength () – inverse• Formula for speed demonstrates this

relationship… c =

c = speed of light = 3.00 x 108 m/s = frequency (Hz) = wavelength (m)

Practice Problem

What is the wavelength of a radio wave with a frequency of 1.01 x 108 Hz?

Practice Problem

An X-ray has a wavelength of 1.15 x 10-10 m. What is its frequency?

Relationships• Frequency and Energy - direct

• Max Planck discovered this:– Electromagnetic radiation is emitted in small bursts, called "quantum“

• Think of a “quantum” as a packet of a specific amount– Each burst (quantum) has energy that depends on the frequency

• E = h is the mathematical formula that relates light and energy

E = energy, measured in Joules (J)h represents Planck’s constanth = 6.626 x 10-34 Js = Frequency, measured in Hertz

Practice problem

• What is the energy of radiation with a frequency of 6.32 x 1020 Hz?

http://blogs.timesofindia.indiatimes.com

Why do fireworks burn with different colors?

Why do fireworks burn with different colors?

Fireworks contain metallic salts. Each metal will emit a different color when vaporized.

http://williamcraigcook.com/fireworks/DiffColors.jpg

http://www.sciencephoto.com

Why do fireworks burn with different colors?

http://www.webexhibits.org

Photons (particle of light) are emitted from an atom when electrons move from a higher potential energy level to a lower potential energy level

Why do fireworks burn with different colors?

http://williamcraigcook.com/fireworks/DiffColors.jpg

The relative frequency, wavelength and energy of the photon is associated with the color of light emitted.

• Bohr Model

Electron in an Atom

hyperphysics.phy-astr.gsu.edu

Hydrogen atom absorbs energy equal to the energy of the photon of violet, blue-green and red light.

This causes the hydrogen electron to move from its ground state to an excited state.

The electron returns to its ground state and releases energy resulting in the emission spectra.

Ground state vs. Excited State Electrons

Absorption of Energy

Release of Energy (Emission)

hyperphysics.phy-astr.gsu.edu

Electrons and LightQuantum Leap

When a valence electron absorbs energy (from heat or electricity), it “jumps” to a higher energy level (excited state). This jump is called a quantum leap.

It is unstable at this excited state and cannot stay there.

When is light emitted? When it falls back to a stable

energy level (ground state), it releases the energy it previously absorbed. This energy is emitted as a photon of light.

Atoms and Photons and Color• Each atom’s electrons “jump” to certain excited

states. • Each “fall” releases a photon of a certain energy,

frequency, and wavelength which correspond to colors of light.

• ATOMIC EMISSION SPECTRUM: the colors of light emitted by an atom’s electrons, and it can be used to identify the element.