History of the Atom…Part 2 Left off with Rutherford’s Gold Foil Experiment… Conclusions from it Left off with Rutherford’s Gold Foil Experiment… Conclusions from it Atom is mostly empty space vs. JJ Thomson’s solid plum-pudding model Atom is mostly empty space vs. JJ Thomson’s solid plum-pudding model There was a very small center that was termed the Nucleus There was a very small center that was termed the Nucleus Since the overall electrical charge of the atom is neutral, a positively charged nucleus must offset the negative charge of the electrons Since the overall electrical charge of the atom is neutral, a positively charged nucleus must offset the negative charge of the electrons

Where are the Rutherford Electrons? Rutherford kept up with the recent advances in physics dealing with charged particles and radiation Rutherford kept up with the recent advances in physics dealing with charged particles and radiation Rutherford in 1911 concluded that the electrons circled the nucleus like the planets do the Sun Rutherford in 1911 concluded that the electrons circled the nucleus like the planets do the Sun So that solves the issue? So that solves the issue? Not really Not really

One problem with this model: how do we explain that the electrons are located outside the nucleus? One problem with this model: how do we explain that the electrons are located outside the nucleus? Why do they stay there? Why do they stay there? If the electrons were stationary, they would be attracted by the positive charge of the nucleus into it If the electrons were stationary, they would be attracted by the positive charge of the nucleus into it If they were moving than they would be ok; correct? If they were moving than they would be ok; correct?

No, because classical mechanics predicts the electrons would lose energy and spiral inward towards the nucleus No, because classical mechanics predicts the electrons would lose energy and spiral inward towards the nucleus To the rescue, experimentation with hydrogen gas To the rescue, experimentation with hydrogen gas When energy is added to hydrogen gas, gives off light which hen passed through a prism gives off a distinct emission spectrum When energy is added to hydrogen gas, gives off light which hen passed through a prism gives off a distinct emission spectrum

SIDEBAR– Light & Spectra Light is one form of electromagnetic radiation Light is one form of electromagnetic radiation There is a continuous spectrum of this energy form; we classify it into different types There is a continuous spectrum of this energy form; we classify it into different types Gamma Radiation is the type of electromagnetic radiation with the most energy Gamma Radiation is the type of electromagnetic radiation with the most energy Next comes X-ray Next comes X-ray Followed by Ultraviolet Followed by Ultraviolet

Visible Light or White Light is that electromagnetic radiation that our human eyes detect; it is less energetic than ultraviolet Visible Light or White Light is that electromagnetic radiation that our human eyes detect; it is less energetic than ultraviolet The Visible Light can be separated into different color bands: Their sequence The Visible Light can be separated into different color bands: Their sequence ROY G BIV is a mnemonic to remember the order from least energetic to most ROY G BIV is a mnemonic to remember the order from least energetic to most Above Visible Light in descending order of energy comes Infrared, Microwaves, and Radio waves Above Visible Light in descending order of energy comes Infrared, Microwaves, and Radio waves

Electromagnetic Spectrum

Electromagnetic Waves Light is an electromagnetic wave because it exhibits the property of diffraction Light is an electromagnetic wave because it exhibits the property of diffraction All waves, regardless of type, has several parts: All waves, regardless of type, has several parts: Wavelength- Wavelength- Frequency - Frequency - Amplitude - Amplitude -

Crest – top of the wave Crest – top of the wave Trough – bottom of the wave Trough – bottom of the wave Normal – midpoint between crest and trough Normal – midpoint between crest and trough Wavelength – the distance from a point on one wave to the corresponding point on an adjacent wave (check next slide carefully) Wavelength – the distance from a point on one wave to the corresponding point on an adjacent wave (check next slide carefully) Frequency – the number of waves that pass a given point in one second; often referred to as the number of cycles Frequency – the number of waves that pass a given point in one second; often referred to as the number of cycles

Wave Diagram

Amplitude- the vertical distance from the normal (midpoint) to the top of the wave or to the trough Amplitude- the vertical distance from the normal (midpoint) to the top of the wave or to the trough Represents different properties depending on the type of wave Represents different properties depending on the type of wave Sound – Loudness Sound – Loudness Oceanic – Height of the wave Oceanic – Height of the wave Light – Brightness Light – Brightness For electromagnetic radiation we are only concerned with frequency and wavelength For electromagnetic radiation we are only concerned with frequency and wavelength

Units of Measurement Wavelength – meter or nanometer Wavelength – meter or nanometer Nanometer = 1/ of a meter Nanometer = 1/ of a meter Said another way: 1 m = 1 x 10 9 nm Said another way: 1 m = 1 x 10 9 nm Frequency – Hertz, abbreviated Hz Frequency – Hertz, abbreviated Hz Think of 1 Hz = wave/second or cycle/second; some books write this using seconds only; giving you: s -1 Think of 1 Hz = wave/second or cycle/second; some books write this using seconds only; giving you: s -1

How fast is LIGHT? The speed of light is 3.00 x 10 8 m/s The speed of light is 3.00 x 10 8 m/s Symbol is “c” Symbol is “c” Related to frequency and wavelength Related to frequency and wavelength Their product = speed of light Their product = speed of light Formula: Formula: c = frequency x wavelength c = frequency x wavelength Frequency = v = Greek letter nu Frequency = v = Greek letter nu Wavelength =λ = Greek letter lambda Wavelength =λ = Greek letter lambda

Wavelength-Frequency Problem HINTS Change your frequency from hertz to waves per second or cycles per second Change your frequency from hertz to waves per second or cycles per second waves waves s s Write the wavelength as meters per wave or meters per cycle Write the wavelength as meters per wave or meters per cycle m. m. wave wave

Important relationship Important relationship The greater the frequency the greater the energy – check your textbook for the EM Spectrum The greater the frequency the greater the energy – check your textbook for the EM Spectrum If the frequency goes up the wavelength get shorter If the frequency goes up the wavelength get shorter If the wavelength get longer the frequency decreases If the wavelength get longer the frequency decreases Remember the product of the frequency and wavelength is a constant- the speed of light Remember the product of the frequency and wavelength is a constant- the speed of light

Duality of Light We already have seen that light behaves as a wave We already have seen that light behaves as a wave But it also acts as a PARTICLE But it also acts as a PARTICLE Why? Why? Because the properties of a wave can not explain many interactions with matter such as blackbody radiation and the photoelectric effect Because the properties of a wave can not explain many interactions with matter such as blackbody radiation and the photoelectric effect

Both involve the emission of electromagnetic radiation in discrete packets- not as a continuous spectrum Both involve the emission of electromagnetic radiation in discrete packets- not as a continuous spectrum As iron gets hotter and hotter it color changes- black at room temperature, red when heated, and blue at higher temperatures; not a gradual change of the spectral colors As iron gets hotter and hotter it color changes- black at room temperature, red when heated, and blue at higher temperatures; not a gradual change of the spectral colors Observed by Max Planck, a German, in the 1900, who further studied this phenomena Observed by Max Planck, a German, in the 1900, who further studied this phenomena

Particle Nature of Light Matter can gain or lose energy only in small, specific amounts called quanta Matter can gain or lose energy only in small, specific amounts called quanta A quantum is the minimum amount of energy that can be gained or lost by an atom A quantum is the minimum amount of energy that can be gained or lost by an atom Referred to as Quantized Energy Referred to as Quantized Energy Established the relationship between E quantum = Planck’s Constant x Frequency Established the relationship between E quantum = Planck’s Constant x Frequency

Notice that the amount of energy goes up as the frequency increases Notice that the amount of energy goes up as the frequency increases According to Planck, for a given frequency, matter can emit or absorb energy in whole number multiples of the product of the constant times the frequency According to Planck, for a given frequency, matter can emit or absorb energy in whole number multiples of the product of the constant times the frequency Albert Einstein also joined the discussion adding that the photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy Albert Einstein also joined the discussion adding that the photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy

Units of Energy is joule (J) defined as a newton meter Units of Energy is joule (J) defined as a newton meter J = kg · m 2 J = kg · m 2 s 2 s 2 Planck’s Constant = x J·s Planck’s Constant = x J·s Some books give the units as J/Hz Some books give the units as J/Hz Remembering Hz = waves/s the first equation is equivalent as is the following Remembering Hz = waves/s the first equation is equivalent as is the following Planck’s constant, h = x J·s Planck’s constant, h = x J·s wave wave

Even though the E quantum is related to Planck’s constant times the EM frequency, remember that frequency is related to the wavelength via the speed of light Even though the E quantum is related to Planck’s constant times the EM frequency, remember that frequency is related to the wavelength via the speed of light Therefore we can summarize the relationship between electromagnetic energy and an electron as follows: Therefore we can summarize the relationship between electromagnetic energy and an electron as follows: An EM wave of a certain frequency has only one possible wavelength An EM wave of a certain frequency has only one possible wavelength

Back to Bohr Since he observed the spectral lines given off from hydrogen gas he concluded that there were specified energy levels in an atom Since he observed the spectral lines given off from hydrogen gas he concluded that there were specified energy levels in an atom He proposed the Orbit Model which is an extension of Rutherford’s Planetary model He proposed the Orbit Model which is an extension of Rutherford’s Planetary model Are we finally done? Are we finally done?

No No That’s where we are going next- That’s where we are going next-