History of the Atom…Part 2History of the Atom…Part 2 Left off with Rutherford’s Gold Foil Left off with Rutherford’s Gold Foil

Experiment… Conclusions from itExperiment… Conclusions from it Atom is mostly empty space vs. JJ Atom is mostly empty space vs. JJ

Thomson’s solid plum-pudding Thomson’s solid plum-pudding modelmodel

There wasThere was a very small center that a very small center that was termed the Nucleuswas termed the Nucleus

Since the overall electrical charge Since the overall electrical charge of the atom is neutral, a positively of the atom is neutral, a positively charged nucleus must offset the charged nucleus must offset the negative charge of the electronsnegative charge of the electrons

Where are the Rutherford Where are the Rutherford Electrons?Electrons?

Rutherford kept up with the recent Rutherford kept up with the recent advances in physics dealing with advances in physics dealing with charged particles and radiationcharged particles and radiation

Rutherford in 1911 concluded that Rutherford in 1911 concluded that the electrons circled the nucleus the electrons circled the nucleus like the planets do the Sunlike the planets do the Sun

So that solves the issue? So that solves the issue? Not reallyNot really

One problem with this model: One problem with this model: how do we explain that the how do we explain that the electrons are located outside electrons are located outside the nucleus?the nucleus?

Why do they stay there?Why do they stay there? If the electrons were stationary, If the electrons were stationary,

they would be attracted by the they would be attracted by the positive charge of the nucleus positive charge of the nucleus into itinto it

If they were moving than they If they were moving than they would be ok; correct?would be ok; correct?

No, because classical mechanics No, because classical mechanics predicts the electrons would lose predicts the electrons would lose energy and spiral inward towards energy and spiral inward towards the nucleusthe nucleus

To the rescue, experimentation To the rescue, experimentation with hydrogen gaswith hydrogen gas

When energy is added to When energy is added to hydrogen gas, gives off light hydrogen gas, gives off light which hen passed through a prism which hen passed through a prism gives off a distinct emission gives off a distinct emission spectrumspectrum

SIDEBAR– Light & SIDEBAR– Light & SpectraSpectra

Light is one form of Light is one form of electromagnetic radiationelectromagnetic radiation

There is a continuous spectrum There is a continuous spectrum of this energy form; we classify of this energy form; we classify it into different typesit into different types

Gamma Radiation is the type of Gamma Radiation is the type of electromagnetic radiation with electromagnetic radiation with the most energythe most energy

Next comes X-ray Next comes X-ray Followed by UltravioletFollowed by Ultraviolet

Visible Light or White Light is that Visible Light or White Light is that electromagnetic radiation that our electromagnetic radiation that our human eyes detect; it is less energetic human eyes detect; it is less energetic than ultravioletthan ultraviolet

The Visible Light can be separated The Visible Light can be separated into different color bands: Their into different color bands: Their sequencesequence

ROY G BIV is a mnemonic to remember ROY G BIV is a mnemonic to remember the order from least energetic to mostthe order from least energetic to most

Above Visible Light in descending Above Visible Light in descending order of energy comesorder of energy comes Infrared, Infrared, Microwaves, and Radio wavesMicrowaves, and Radio waves

Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic WavesElectromagnetic Waves

Light is an electromagnetic wave Light is an electromagnetic wave because it exhibits the property because it exhibits the property of diffractionof diffraction

All waves, regardless of type, All waves, regardless of type, has several parts:has several parts:

Wavelength-Wavelength- Frequency -Frequency - Amplitude -Amplitude -

Crest – top of the waveCrest – top of the wave Trough – bottom of the waveTrough – bottom of the wave Normal – midpoint between crest Normal – midpoint between crest

and troughand trough Wavelength – the distance from a Wavelength – the distance from a

point on one wave to the point on one wave to the corresponding point on an adjacent corresponding point on an adjacent wave (check next slide carefully)wave (check next slide carefully)

Frequency – the number of waves Frequency – the number of waves that pass a given point in one that pass a given point in one second; often referred to as the second; often referred to as the number of cyclesnumber of cycles

Wave DiagramWave Diagram

Amplitude- the vertical distance from Amplitude- the vertical distance from the normal (midpoint) to the top of the normal (midpoint) to the top of the wave or to the troughthe wave or to the trough

Represents different properties Represents different properties depending on the type of wavedepending on the type of wave

Sound – LoudnessSound – Loudness Oceanic – Height of the waveOceanic – Height of the wave Light – BrightnessLight – Brightness For electromagnetic radiation we are For electromagnetic radiation we are

only concerned with frequency and only concerned with frequency and wavelengthwavelength

Units of MeasurementUnits of Measurement Wavelength – meter or nanometerWavelength – meter or nanometer Nanometer = 1/1 000 000 000 of a Nanometer = 1/1 000 000 000 of a

metermeter Said another way: 1 m = 1 x 10Said another way: 1 m = 1 x 1099 nm nm

Frequency – Hertz, abbreviated HzFrequency – Hertz, abbreviated Hz Think of 1 Hz = wave/second or Think of 1 Hz = wave/second or

cycle/second; some books write this cycle/second; some books write this using seconds only; giving you: susing seconds only; giving you: s-1-1

How fast is LIGHT?How fast is LIGHT?

The speed of light is 3.00 x 10The speed of light is 3.00 x 1088m/sm/s Symbol is “Symbol is “c”c” Related to frequency and wavelengthRelated to frequency and wavelength Their product = speed of lightTheir product = speed of light Formula:Formula: cc = frequency x wavelength = frequency x wavelength Frequency = v = Greek letter nuFrequency = v = Greek letter nu Wavelength =Wavelength =λλ = Greek letter lambda = Greek letter lambda

Wavelength-Frequency Wavelength-Frequency ProblemProblemHINTSHINTS

Change your frequency from Change your frequency from hertz to waves per second or hertz to waves per second or cycles per secondcycles per second

waves waves ss Write the wavelength as meters Write the wavelength as meters

per wave or meters per cycleper wave or meters per cycle m . m . wavewave

Important relationshipImportant relationship The greater the frequency the The greater the frequency the

greater the energy – check your greater the energy – check your textbook for the EM Spectrumtextbook for the EM Spectrum

If the frequency goes up the If the frequency goes up the wavelength get shorterwavelength get shorter

If the wavelength get longer the If the wavelength get longer the frequency decreasesfrequency decreases

Remember the product of the Remember the product of the frequency and wavelength is a frequency and wavelength is a constant- the speed of lightconstant- the speed of light

Duality of LightDuality of Light

We already have seen that light We already have seen that light behaves as a wavebehaves as a wave

But it also acts as a PARTICLEBut it also acts as a PARTICLE Why?Why? Because the properties of a wave Because the properties of a wave

can not explain many interactions can not explain many interactions with matter such as blackbody with matter such as blackbody radiation and the photoelectric radiation and the photoelectric effecteffect

Both involve the emission of Both involve the emission of electromagnetic radiation in electromagnetic radiation in discrete packets- not as a discrete packets- not as a continuous spectrumcontinuous spectrum

As iron gets hotter and hotter it As iron gets hotter and hotter it color changes- black at room color changes- black at room temperature, red when heated, and temperature, red when heated, and blue at higher temperatures; not a blue at higher temperatures; not a gradual change of the spectral gradual change of the spectral colorscolors

Observed by Max Planck, a Observed by Max Planck, a German, in the 1900, who further German, in the 1900, who further studied this phenomenastudied this phenomena

Particle Nature of LightParticle Nature of Light

Matter can gain or lose energy only in Matter can gain or lose energy only in small, specific amounts called small, specific amounts called quantaquanta

A A quantum quantum is the minimum amount of is the minimum amount of energy that can be gained or lost by energy that can be gained or lost by an atoman atom

Referred to as Quantized Energy Referred to as Quantized Energy Established the relationship between Established the relationship between

EEquantumquantum= Planck’s Constant x = Planck’s Constant x FrequencyFrequency

Notice that the amount of energy Notice that the amount of energy goes up as the frequency goes up as the frequency increasesincreases

According to Planck, for a given According to Planck, for a given frequency, matter can emit or frequency, matter can emit or absorb energy in whole number absorb energy in whole number multiples of the product of the multiples of the product of the constant times the frequencyconstant times the frequency

Albert Einstein also joined the Albert Einstein also joined the discussion adding that the discussion adding that the photonphoton is a particle of electromagnetic is a particle of electromagnetic radiation with no mass that radiation with no mass that carries a quantum of energycarries a quantum of energy

Units of Energy is joule (J) defined as Units of Energy is joule (J) defined as a newton metera newton meter

J = J = kg · m kg · m22 ss22

Planck’s Constant = 6.626 x 10Planck’s Constant = 6.626 x 10-34-34 J·s J·s Some books give the units as J/HzSome books give the units as J/Hz Remembering Hz = waves/s the first Remembering Hz = waves/s the first

equation is equivalent as is the equation is equivalent as is the followingfollowing

Planck’s constant, Planck’s constant, hh = 6.626 x10 = 6.626 x10-34-34 J·sJ·s

wavewave

Even though the EEven though the Equantumquantum is related is related to Planck’s constant times the EM to Planck’s constant times the EM frequency, remember that frequency, remember that frequency is related to the frequency is related to the wavelength via the speed of lightwavelength via the speed of light

Therefore we can summarize the Therefore we can summarize the relationship between relationship between electromagnetic energy and an electromagnetic energy and an electron as follows:electron as follows:

An EM wave of a certain frequency An EM wave of a certain frequency has only one possible wavelengthhas only one possible wavelength

Back to BohrBack to Bohr

Since he observed the spectral Since he observed the spectral lines given off from hydrogen lines given off from hydrogen gas he concluded that there gas he concluded that there were specified energy levels in were specified energy levels in an atoman atom

He proposed the Orbit Model He proposed the Orbit Model which is an extension of which is an extension of Rutherford’s Planetary modelRutherford’s Planetary model

Are we finally done?Are we finally done?

NoNo

That’s where we are That’s where we are going next-going next-