How much energy is contained in a 10 g piece of copper heated 15 degrees Celcius?

How do fireworks work?Why do the leaves change color?Why don’t atoms collapse?

• What is light?

• What is the relationships exist between light color and elements?

• Thus what is the relationship between Elements and Energy?

What did you see?

What did you hypothesize about the relationship between elements, light, color?

Different elements when energized release a unique amount of light which is displayed as a different color

• What form is light in?• Light behaves as a wave/Particle• The speed of light is constant- 3.00 X

10 8 m/s

The nature of light• Type of Energy• Electromagnetic radiation:

produced by the interaction between electricity and magnetism

• We are going to discuss the wave-like properties.

• Different colors of light have unique wavelength and frequency

Wavelength ()

• The distance between waves

The electromagnetic spectrumconsists of various wave lengths

Frequency nu

• Number of waves that pass a point per second

• Cycles/sec = hertz (hz)

The electromagnetic spectrumconsists of various frequencies

Different colors of light• Have specific frequencies and wavelengths• The relationship is inversely related(as one

increases the other decreases)• C=גv ג(wavelength) v(frequency)• E=hv where h is planck’s constant (6.626X10

-34 JXS)• Thus you can use the relationship of

frequency to solve for wavelength• That’s Nice!!

Quantized light• As an atom is increasingly excited (by heat,

electricity, etc) the color it emits doesn’t change, just the brightness of the light changes

• The energy emitted by one atom is called a photon

• The energy of one photon from one atom can be described by the equation, E = h

• “h”= Planck’s constant = 6.626 X 10-34j.sec• The equation could also be written E = h

C/

• Calculate the frequency of a wave whose wavelengths is 6.0 x 10-5 cm. In what region of the spectrum is the radiation found? 

• Solution Use the equation c = λ x v to solve. Rearrange the terms to isolate the variable for which you must solve. Then substitute and solve.

Back to the lab

• If different colors of light represent a specific amount of energy what do different banding patterns show?

Looking for a new model

What did Rutherford Think?What did he not include in his

model?What needed to be added to the

configuration of the atom?

The problem with the model

• Since the electron is attracted to the protons in the nucleus, and

• Circular orbits require continuous inputs of energy, then atoms should collapse as the electrons spiral into the nucleus!!

• Therefore, the model needed to be re-designed.

Development of the quantum theory (early 1900’s)

• Max Planck: Atoms absorb or emit only certain colors of light. Energy is gained or lost by an atom only in whole number multiples of quantity

• Similar to Climbing Stairs.(You can’t climb half a stair!!)

• In other words, light is QUANTIZED

Quantized light• As an atom is increasingly excited (by heat,

electricity,etc) the color it emits doesn’t change, just the brightness of the light changes

• The energy emitted by one atom is called a photon

• The energy of one photon from one atom can be described by the equation, E = h

• “h”= Planck’s constant = 6.626 X 10-34j.sec• The equation could also be written E = h

C/

Line Spectra

• Atoms emit only certain colors when excited. These are expressed as colored lines when observed through spectroscopes.

• Niels Bohr proposed that this was because electrons could occupy only certain energy levels, described by orbitals.

Emission Spectra of Hydrogen

When excited hydrogen atoms return to a lower energy state, they emit photons of certain energies and thus certain color (Specific wavelengths in nanometers are emitted of the spectrum which correspond to a specific color of band we see)

Line spectra emitted by excited atoms = Evidence of electron activity

Low frequency light (red) High frequency light (violet, UV light)

Ground State = Electrons unexcited, close to nucleus, no light emitted

When atoms are energized (by heat, electricity) electrons begin “hopping”.

1. Must absorb the exact amount of energy in order to make a “hop”.

2. When electron returns to ground state, it emits the exact energy (color) that is absorbed.

• Bohr proposed an equation that accurately predicted the energy emitted by an excited hydrogen atom and correlated the energy with the specific orbitals involved in the “hopping” of the electron.

Hydrogen Emission Spectrum

There are many different energy changes that electrons can make from excited state back to ground state or one excited state to another.

Some release energy in the form of photons of visible light.

• What does brightness of a spectral line represent?

• Why does each element have a unique spectrum?

• Why do you see a different spectrum in incandescent and white light?