The Arrangement of Electrons in Atoms

The Development of the New Atomic Model

The Dual Nature of Light

• Before 1900, scientists thought light behaved solely as a wave.

• We now know that light has particle-like characteristics as well.

• Some properties are best explained by light’s wave nature others by it’s particle nature.

Electromagnetic Radiation

• Includes visible light, x-rays, ultraviolet, infrared light, microwaves and radio waves.

• Exhibits wave like behavior.• Is related to _________ and __________.

What does the name suggest?

Electromagnetic Spectrum

Wave Diagram

Wave Characteristics

• Wavelength- The distance between two consecutive peaks or troughs.

• Frequency- The number of waves that pass a point each second (the unit is the Hertz, Hz). One complete wave or cycle per. second = 1 Hz.

• Velocity- Distance a peak moves in a unit of time.

c = f • velocity = frequency x wavelength• The speed (velocity) of electromagnetic waves is

constant (c).C = 3.0 x 108m/s

• If you know the frequency you can calculate the wavelength and…

• SO WHAT DOES ALL THIS HAVE TO WITH A NEW ATOMIC MODEL??

We are getting to that…It will take some time though.

It took the best minds in science years to explain …it should take us at least a few classes…so do not worry if it does not come easy.

Why do we need to learn about this???

• An understanding of the arrangement of electrons makes it possible to explain/predict the chemistry of the elements…in other words, it will make the rest of the course much easier…

• The more you understand about what things are made of including yourself, the universe and everything in it the more you will appreciate it.

• SO…

c = f• velocity = frequency x wavelength• The speed (velocity) of electromagnetic

waves is constant (c).C = 3.0 x 108m/s

• If you know the frequency you can calculate the wavelength and…

• What do different wavelengths relate to?

DIFFERENT COLORS

• Each different color has a different wavelength.

• How does electromagnetic radiation with a short wavelength effect you?

• How does electromagnetic radiation with a long wavelength effect you?

review the spectrum…

How are wavelength and frequency related???

…as the length of the wave increases the

frequency_______________.

The Photoelectric Effect

• When light shines on certain metals an electric current is produced (electrons are emitted from the metal).

• Only light of a certain minimum frequency can cause electrons to move.

• This could not be explained by the wave theory of light…

Quantum• A small specific amount of energy.• The minimum amount of energy that can

be lost/gained by an atom.• The energy of a quantum is related to its

frequency.E = h f

Energy = Plank’s constant x frequencyh = 6.626 x 10-34 j . s

• Higher frequency higher energy

• Shining light on a metal can liberate electrons from it’s surface.•Easy for violet (high frequency) difficultor impossible for red light (low frequency).

•E = h f …the energy of the light is related to it’s frequency ( high f = high E).•Einstein explained the photoelectric effect…light has a particle nature. High frequency light (violet) consists of ‘particles’ with a high energy (think bowling balls) low frequency light (red) consists of ‘particles’ with a low energy(think ping pong balls).•Particles of light are called photons… defined as a quantum of light energy.

Answer The Following

• Pg 97 # 1,4 & 5• Pg 118 # 4, 6• Pg 119 # 31, 32