Explain the relationship between energy, wavelength, and speed of a wave. How are elements’ atomic spectra similar to humans’ fingerprints. 11/23/2015.

DO NOW

• Explain the relationship between energy, wavelength, and speed of a wave.

How are elements’ atomic spectra

similar to humans’ fingerprints.

OBJECTIVES

DATE: 11/23/2015

Reminders

• Wed. Nov. 24: “Model 4-useful light equations” worksheet

• Mon. Nov. 30: textbook #45-49 on page 166

• Tues, Dec 1: Quiz: Light

H

He

Hg

All

Sodium-23 Atom

11 p+

12 n0

11 e-

Sodium-23 Atom

Energy Level

Particle Nature of Light

• Matter can lose or gain energy but only in small, specific amounts

• Photon–A particle that carries energy that is

gained or lost by an atom

Sodium-23 Atom

Ground State-electrons are in a position of low energy

Excitation of Na Atom

Now the atom is

UNSTABLE

Excited State-electrons are in a position of high energy

Excitation of Na Atom

The atom becomes STABLE again

Ground State-electrons are in a position of low energy

Chemist Humor

Question: Why does hamburger have lower energy than steak?

Answer: Because it’s in the ground state.

Excitation of Electrons• Quantum jump: happens all at once – instantaneously –

because the electron can never exist between levels – not even for a second.

See how an electron dropping from the 3rd level to the 2nd level produced red lightA 4 2 electron drop produces blue lightAnd a 5 2 drop produces violet light

Excitation of Electrons• Electron quickly drops back down to lower level and

gives off a distinct band of light energy.

Parts of a Wave

crest

node / origin

troughwavelength

Amplitude

Parts of a Wave

• Wavelength, λ–The distance

between crests on a wave

–Units = m, cm, nm

Parts of a Wave

• Frequency, ν–The number of waves that pass a

given point per second–Units, Hz

s-1 = A

B

C

Low

High

Medium

1. What is the wavelength of a wave that has frequency of 3.44 x 109 Hz?

2. Light reflected from a green leaf has a wavelength of 4.90 x 10-7 m. What is the ν of the light?

3. What is the energy of a wave with a 𝝀 of 5.89 x 10-7 m?

What is the wavelength of a wave that has frequency of 3.44 x 109 Hz?

1. Write the givens.

2. Write the formula.3. Manipulate formula to

find the unknown.

• Given: ν = 3.44 x 109 λ = ?• Formula:

ν νc = 3.00 x 108

Light reflected from a green leaf has a wavelength of 4.90 x 10-7 m. What is the

frequency of the light?

1. Write the givens.

2. Write the formula.3. Manipulate formula to

find the unknown.

• Given: λ = 4.90 x 10-7 mν = ?• Formula:

c = 3.00 x 108

Light reflected from a green leaf has a wavelength of 4.90 x 10-7 m. What is the

frequency of the light?4. Substitute in known

values and solve.

5. Make sure units are correct.

• Substitute and solve:

𝟏𝒔