THE ELECTRON It is so electrifying Is this physics or is this chemistry? Hummmmmmm!!!! It is so electrifying Is this physics or is this chemistry? Hummmmmmm!!!!

A New Atomic Model Rutherford’s planet system model was an improvement over earlier models, but it was still not complete. –Where are the electrons really? A new model evolved out of the similarities discovered between the behavior of light & electrons. –This new connection led to a revolution in science. Rutherford’s planet system model was an improvement over earlier models, but it was still not complete. –Where are the electrons really? A new model evolved out of the similarities discovered between the behavior of light & electrons. –This new connection led to a revolution in science.

The behavior of an electron can be modeled by the behavior of light. –Light is a type of electromagnetic radiation, that travels through space as a wave. –Other examples are (x-rays, radio waves, gamma-rays, and cellular waves) The behavior of an electron can be modeled by the behavior of light. –Light is a type of electromagnetic radiation, that travels through space as a wave. –Other examples are (x-rays, radio waves, gamma-rays, and cellular waves) The Behavior of Light

All waves, whether they are water waves or electromagnetic waves, can be described in terms of 4 characteristics –Amplitude –Frequency –Wavelength –Speed All waves, whether they are water waves or electromagnetic waves, can be described in terms of 4 characteristics –Amplitude –Frequency –Wavelength –Speed Light as a Wave

speed

Amplitude: –Is the height of the wave measured from the origin to its crest, or peak –The brightness, or intensity of light depends on the amplitude of the light wave. Amplitude: –Is the height of the wave measured from the origin to its crest, or peak –The brightness, or intensity of light depends on the amplitude of the light wave. Light as a Wave

Wavelength ( ): –the distance between successive crests of the wave. –the distance that the wave travels as it completes one full cycle of up and down motion Wavelength ( ): –the distance between successive crests of the wave. –the distance that the wave travels as it completes one full cycle of up and down motion Light as a Wave

Frequency ( ): –How fast the wave oscillates. –Measured by the # of times a light wave completes a cycle of up and down motion per sec. –When a radio station identifies itself it’s the frequency used Frequency ( ): –How fast the wave oscillates. –Measured by the # of times a light wave completes a cycle of up and down motion per sec. –When a radio station identifies itself it’s the frequency used Light as a Wave

Speed ( c ): –Regardless of its wavelength, moves through space as a constant speed 3.00x10 8 m/s –Because light moves at a constant speed there is a relationship between frequency and wavelength Speed ( c ): –Regardless of its wavelength, moves through space as a constant speed 3.00x10 8 m/s –Because light moves at a constant speed there is a relationship between frequency and wavelength Light as a Wave

It is a mathematical relationship between wavelength and the freq- uency of a wave. –The shorter the wavelength the higher the frequency –The longer the wavelength the lower the frequency Calculated using the equation: It is a mathematical relationship between wavelength and the freq- uency of a wave. –The shorter the wavelength the higher the frequency –The longer the wavelength the lower the frequency Calculated using the equation: Light as a Wave

When white light passes through a prism or through raindrops you might have noticed that the light can be separated into a continuous array or spectrum of colors –All the mixture of wavelengths that make up white light are spread apart When white light passes through a prism or through raindrops you might have noticed that the light can be separated into a continuous array or spectrum of colors –All the mixture of wavelengths that make up white light are spread apart Light as a Wave

The colors that combine to form white light are red, orange, yellow, green, blue, indigo, and violet (ROYGBIV) The different colors have different wavelengths and frequencies –Shortest & highest = violet –Longest & lowest = red The colors that combine to form white light are red, orange, yellow, green, blue, indigo, and violet (ROYGBIV) The different colors have different wavelengths and frequencies –Shortest & highest = violet –Longest & lowest = red Light as a Wave

Visible light only constitutes a tiny portion of the total light spectrum. –The rest of the electromagnetic spec- trum is invisible to the naked eye The next slide shows the relative positions of the various types of EM radiation in the EM spectrum Visible light only constitutes a tiny portion of the total light spectrum. –The rest of the electromagnetic spec- trum is invisible to the naked eye The next slide shows the relative positions of the various types of EM radiation in the EM spectrum Light as a Wave

Scientists soon discovered that elements can also produce light or an electromagnetic spectra. –If you energize gaseous elements like hydrogen and then diffract the light produced through a prism the result is an EM spectrum, some of which is in the visible range Scientists soon discovered that elements can also produce light or an electromagnetic spectra. –If you energize gaseous elements like hydrogen and then diffract the light produced through a prism the result is an EM spectrum, some of which is in the visible range Light as a Wave

But instead of the spectrum being continuous (one color bleeding into the next) the spectrum splits into a pattern of individual lines. –It’s not a mixture of all wavelengths, but a mixture of specific, individual wavelengths But instead of the spectrum being continuous (one color bleeding into the next) the spectrum splits into a pattern of individual lines. –It’s not a mixture of all wavelengths, but a mixture of specific, individual wavelengths Only specific wavelengths of color in the mixture Only specific wavelengths of color in the mixture Light as a Wave

Scientist’s had a hard time explaining this line spectra –Why were they specific lines of color instead of all the colors? Finally along came a free thinking scientist named Max Planck, –He developed a new theory that is the basis of modern physics. A.K.A. Quantum Theory. Scientist’s had a hard time explaining this line spectra –Why were they specific lines of color instead of all the colors? Finally along came a free thinking scientist named Max Planck, –He developed a new theory that is the basis of modern physics. A.K.A. Quantum Theory. Quantum Theory

Planck hypothesized that energy, instead of being given off in contin- uous waves of energy, is given off in little packets of energy, or quanta. –The word quantum means a fixed amount, think of it as flashes of energy –Also called a photon when describing a quantum of light Planck hypothesized that energy, instead of being given off in contin- uous waves of energy, is given off in little packets of energy, or quanta. –The word quantum means a fixed amount, think of it as flashes of energy –Also called a photon when describing a quantum of light Quantum Theory

Planck’s idea was that one quantum of energy (light) was related to its frequency by the equation: E = h The constant h (planck’s constant) has a value of x J-s, E is the energy, and is the frequency of the radiation. –The energy in wave form that is abs- orbed or emitted by atoms, is restrict- ed to specific quantities (quantized) Planck’s idea was that one quantum of energy (light) was related to its frequency by the equation: E = h The constant h (planck’s constant) has a value of x J-s, E is the energy, and is the frequency of the radiation. –The energy in wave form that is abs- orbed or emitted by atoms, is restrict- ed to specific quantities (quantized) Quantum Theory

When we think of energy increasing, or being absorbed, we usually think of it increasing continuously. Quantum Theory If you accelerate in a car, you are accustomed to your speed increasing from 0 to 60 mph continuously…

When we think of energy increasing, or being absorbed, we usually think of it increasing continuously. Quantum Theory But Planck’s theory means that energy increases in discrete levels (like steps)

At the atomic level it might be like being at rest (0 mph) and pressing the accelerator Quantum Theory –If enough energy is absorbed then the car leaps to 10 mph –When enough energy has been absorbed the car leaps to 20 mph –When enough energy has been absorbed the car leaps to 30 mph…

Planck’s understanding works because of the size of planck’s constant (h). –Each quantum (leap) is , so it feels like a continuous change of energy at the macroscopic level –Just like a drawn line with a computer looks smooth unless you zoom in to see it is actually blocks Planck’s understanding works because of the size of planck’s constant (h). –Each quantum (leap) is , so it feels like a continuous change of energy at the macroscopic level –Just like a drawn line with a computer looks smooth unless you zoom in to see it is actually blocks Quantum Theory

Planck’s theory of quantized energy was a revolutionary idea, but most scientists didn’t get it. Albert Einstein saw the potential of quantized energy and proposed it to be a new way of understanding light. –He needed Planck’s work to explain his Nobel Prize winning research on the photoelectric effect. Planck’s theory of quantized energy was a revolutionary idea, but most scientists didn’t get it. Albert Einstein saw the potential of quantized energy and proposed it to be a new way of understanding light. –He needed Planck’s work to explain his Nobel Prize winning research on the photoelectric effect. Quantum Theory

Scientists noticed that when you shined light onto some types of metal, a voltage could be measured –The light seems to transfer its energy to the metal which causes an electric current But, not every kind of light would cause this to happen –And it doesn’t help to initiate the current by making the light brighter Scientists noticed that when you shined light onto some types of metal, a voltage could be measured –The light seems to transfer its energy to the metal which causes an electric current But, not every kind of light would cause this to happen –And it doesn’t help to initiate the current by making the light brighter Photoelectric Effect

For each metal, a minimum frequency of light is needed to release e - –Red light cannot produce a current –but violet can produce a current For each metal, a minimum frequency of light is needed to release e - –Red light cannot produce a current –but violet can produce a current Photoelectric Effect

Einstein hypothesized that light must exist as quantized energy –Light must act as a collection of part- icles for it to have the ability to collide with E - s at the surface of metal with the power to drive the electrons out When a photon of light strikes a metal electron, it acts much like a billiard ball –The e - is then knocked out of the atom which causes an electrical current Einstein hypothesized that light must exist as quantized energy –Light must act as a collection of part- icles for it to have the ability to collide with E - s at the surface of metal with the power to drive the electrons out When a photon of light strikes a metal electron, it acts much like a billiard ball –The e - is then knocked out of the atom which causes an electrical current Photoelectric Effect

Einstein reasoned that the energy (and thus the frequency) of the photon det- ermines whether or not it has sufficient energy to knock an e - from the atom. –There is a minimum frequency of light required to establish a current –Which explains why x-rays are dam- aging to organisms, while radio waves have low frequencies and aren’t hazardous. Einstein reasoned that the energy (and thus the frequency) of the photon det- ermines whether or not it has sufficient energy to knock an e - from the atom. –There is a minimum frequency of light required to establish a current –Which explains why x-rays are dam- aging to organisms, while radio waves have low frequencies and aren’t hazardous. Photoelectric Effect

The idea that light is a wave that trav- els at the speed of light, is now coupl- ed with the fact that light can also act as a particle –Light can be thought of as a tiny ball which can collide with an electron Light exhibits the properties of both particles and waves. The idea that light is a wave that trav- els at the speed of light, is now coupl- ed with the fact that light can also act as a particle –Light can be thought of as a tiny ball which can collide with an electron Light exhibits the properties of both particles and waves. Wave…I mean…Particle…I mean…

Realizing that atoms can also gain or lose energy in chunks or quanta, helps us answer the question of how electrons are arranged in the atom. –Remember earlier we said that if you split the light given off by H 2 gas with a prism you see set of colored lines instead of a continuous spectrum. This would only happen if the energy of an electron is quantized Realizing that atoms can also gain or lose energy in chunks or quanta, helps us answer the question of how electrons are arranged in the atom. –Remember earlier we said that if you split the light given off by H 2 gas with a prism you see set of colored lines instead of a continuous spectrum. This would only happen if the energy of an electron is quantized Electrons and Quantum Theory

Every element, when excited, emits or absorbs light –If emitted the light contains a unique collection wavelengths –If absorbed the light absorbs the same pattern of wavelengths This gives each element a fingerprint of spectral lines. Every element, when excited, emits or absorbs light –If emitted the light contains a unique collection wavelengths –If absorbed the light absorbs the same pattern of wavelengths This gives each element a fingerprint of spectral lines. Electrons and Quantum Theory

Scientists began to try to explain the occurrence of the line spectra Neils Bohr put Rutherford’s atomic model & Planck’s quantum theory together to begin to explain the line spectra –Rutherford described the atom as a planetary system with the nucleus acting as the sun and the electrons orbiting much like planets. Scientists began to try to explain the occurrence of the line spectra Neils Bohr put Rutherford’s atomic model & Planck’s quantum theory together to begin to explain the line spectra –Rutherford described the atom as a planetary system with the nucleus acting as the sun and the electrons orbiting much like planets. Electrons and Quantum Theory

Bohr decided that the planetary model couldn’t adequately explain the occurrence of the spectral phenomena –He reasoned that in order to get the individual lines of energy released in line spectra the energy of the e - must be quantized. –The electron is permitted to have only certain orbits corresponding to differ- ent levels of energy. Bohr decided that the planetary model couldn’t adequately explain the occurrence of the spectral phenomena –He reasoned that in order to get the individual lines of energy released in line spectra the energy of the e - must be quantized. –The electron is permitted to have only certain orbits corresponding to differ- ent levels of energy. Electrons and Quantum Theory

Bohr labeled each energy level, or orbit, by a number, n. –an atom with its e - s occupying their lowest energy levels the ground state If an e - at any level absorbs a parti- cular amount of energy, it leaps to a level of higher energy, an excited state –The excited e- will return to ground state & release its absorbed energy Bohr labeled each energy level, or orbit, by a number, n. –an atom with its e - s occupying their lowest energy levels the ground state If an e - at any level absorbs a parti- cular amount of energy, it leaps to a level of higher energy, an excited state –The excited e- will return to ground state & release its absorbed energy Electrons and Quantum Theory

The energy released as the e - falls back to ground state might be released as a photon in the visible range (color). –The more energy absorbed by the e - the higher the leap in energy The higher the leap - the farther the electron falls Each fall; leads to specific frequencies; therefore specific lines of color The energy released as the e - falls back to ground state might be released as a photon in the visible range (color). –The more energy absorbed by the e - the higher the leap in energy The higher the leap - the farther the electron falls Each fall; leads to specific frequencies; therefore specific lines of color Electrons and Quantum Theory

Bohr used his theory to calculate the frequencies & wavelengths emitted by excited H atoms accurately –which was powerful evidence in support of his model. –It only worked successfully for Hydrogen Bohr used his theory to calculate the frequencies & wavelengths emitted by excited H atoms accurately –which was powerful evidence in support of his model. –It only worked successfully for Hydrogen Electrons and Quantum Theory

Planck’s & Einstein’s theories lead us to an understanding of the light as a wave & as a discrete particle. –When light travels through space it has wavelike properties. –When it interacts with matter its behavior can be described as like a stream of particles. Planck’s & Einstein’s theories lead us to an understanding of the light as a wave & as a discrete particle. –When light travels through space it has wavelike properties. –When it interacts with matter its behavior can be described as like a stream of particles. Light = Wave & Particle

If EM radiation has properties of waves and particles, maybe matter does too. –This connection was made by Louis de Broglie Louis de Broglie reasoned that even particles of matter can behave like waves and at times exhibit the charac- teristics of a wave, much like light. If EM radiation has properties of waves and particles, maybe matter does too. –This connection was made by Louis de Broglie Louis de Broglie reasoned that even particles of matter can behave like waves and at times exhibit the charac- teristics of a wave, much like light. Matter = Wave & Particle

He developed a relationship between the mass & velocity of a particle and the wavelength it would exhibit – = h/mv. The eqn predicts that all objects in motion have wavelike behavior –it is only noticeable in objects with a tiny mass. –scientists routinely use this theory of electrons having wavelike nature to magnify objects He developed a relationship between the mass & velocity of a particle and the wavelength it would exhibit – = h/mv. The eqn predicts that all objects in motion have wavelike behavior –it is only noticeable in objects with a tiny mass. –scientists routinely use this theory of electrons having wavelike nature to magnify objects Matter = Wave & Particle