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Modern Atomic Model. Electron modeling…. To understand electrons, scientists began comparing them to light. Behavior of light. Light is a wave – similar to water waves Visible light belongs to electromagnetic spectrum. High energy. Low energy. Low Frequency. High Frequency. Spectrum.
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Electron modeling… • To understand electrons, scientists began comparing them to light.
Behavior of light • Light is a wave – similar to water waves • Visible light belongs to electromagnetic spectrum
High energy Low energy Low Frequency High Frequency Spectrum X-Rays Radiowaves Microwaves Ultra-violet GammaRays Infrared . Long Wavelength Short Wavelength Visible Light
Behavior of light • All forms of EMR travel at a constant speed of 3.0 x 108 m/s, when in a vacuum. This value also works for the speed of light in air (because air is mostly a vacuum).
Behavior of light Waves can be described in terms of the following: • Wavelength • Frequency • Amplitude • Speed
Behavior of light Waves can be described in terms of the following: • Wavelength - , distance between successive crests (or any 2 corresponding points), for visible light = 400-750 nm
Behavior of light • Frequency - the number of waves that pass a given point per second, units are cycles/sec or hertz (Hz), abbreviated n - the Greek letter nu c = ln
Behavior of light • Amplitude – height from origin to crest
Behavior of light • Speed – measured in m/s, light moves @ constant speed of 3.0 x 108 m/s, abbreviated as c
Crest Wavelength Amplitude Trough Parts of a wave Origin
Parts of Wave • Origin - the base line of the energy. • Crest - high point on a wave • Trough - Low point on a wave • Amplitude - distance from origin to crest • Wavelength - distance from crest to crest, abbreviated l (Greek letter lambda)
Behavior of light • Because light has a constant speed, we get a relationship between & (c = )
Frequency and wavelength • Are inversely related • As one goes up, the other goes down. • Different frequencies of light go with different colors of light. • There is a wide variety of frequencies • The whole range is called a continuous spectrum
Behavior of light Question 1: If light has = 633 nm, what is ? Question 2: Red light travels at 3.0 x 108 m/s and has a l of 700 nm. What is n? Question 3: Violet light has a n of 7.5 x 1014 Hz. What is l?
Wave model problems The wave model of light worked well until the beginning of the 20th century. This is because some scientists were observing light and found that what they saw did not fit the wave model.
Wave model problems Black body radiation • In 1900, Max Planck was studying radiation given off when matter was heated. The physics he knew said that matter could absorb or emit any quantity of energy. The results of his experiments did not fit with that idea.
Light is a Particle • Energy is quantized. • Light is energy • Light must be quantized • These smallest pieces of light are called photons. • Energy and frequency are directly related.
Wave model problems • A quantum of light was later called a photon. Radiation is emitted or absorbed in whole numbers of photons.
Wave model problems • To relate the quantum of energy and the frequency of the radiation, he created the relationship E = h.
Energy and frequency • E = h x n • E is the energy of the photon • nis the frequency • h is Planck’s constant • h = 6.626 x 10 -34 Joules × seconds
Wave model problems • What energy is given off when your stove coils turn red? (Remember that red light has a frequency of 4.29 x 1014 Hz.) • Which has greater energy – red or violet light?
Wave model problems • Planck’s ideas were not immediately accepted. It was not until some time later that Albert Einstein used Planck’s equation to work on solving the photoelectric effect.
Wave model problems Photoelectric effect • Light shining on certain metals can eject electrons.
Wave model problems Photoelectric effect • The fact that light was able to knock electrons loose wasn’t a problem. What wave theory couldn’t explain was why only certain frequencies of light (or higher) could knock out electrons.
Wave model problems Photoelectric effect • Einstein proposed that light consisted of energy quanta that behaved as particles – not waves. The quanta were called photons.
Wave model problems Photoelectric effect • The photoelectric effect problem was then solved by the idea that radiation is emitted or absorbed in whole numbers of photons or radiation particles.
Wave model problems Photoelectric effect • It was later proven that light could definitely act as a particle. So, we now have light acting as both a wave and as particles. (This will be the basis for understanding how e- behave.)
Atomic Spectrum What color tells us about atoms
Prism • White light is made up of all the colors of the visible spectrum. • Passing it through a prism separates it.
If the light entering the prism is not white… • By heating a gas or using electricity, we can get the gas to give off colors • Passing this light through a prism does something different than white light
Atomic Spectrum • Each element gives off its own characteristic colors • Can be used to identify the element • How we know what stars are made of
Wave model problems Bright line spectrum • Scientists noticed that you could vaporize an element in a flame to produce different flame colors. You can then use a prism to sort the colors to produce a line spectrum (only certain colors are produced).
Wave model problems Bright line spectrum • Problem: Each element produced a different line spectrum.
These are called line spectra • They are unique to each element. • These are emission spectra (the light is emitted or given off)
Rutherford’s Model • Discovered the nucleus • Small dense and positive • Electrons around nucleus in electron cloud
Bohr’s Model • Why don’t the electrons fall into the nucleus? • Move like planets around the sun. • In circular orbits at different levels. • Energy separates one level from another.
Bohr’s Model Nucleus Electron Orbit Energy Levels
Bohr’s Model } • Further away from the nucleus means more energy. • There is no “in between” energy • Energy is in Levels Fifth Fourth Third Increasing energy Second First Nucleus
Bohr Model • Niels Bohr was able to explain the bright line spectrum. To do so, he created a model with the following parts: • The e- could orbit the nucleus only in allowed paths or orbits.
Bohr Model • The H atom has set energy possibilities that depend on which orbit the e- occupies. • The ground state occurs when the e- is in the orbit closest to the nucleus.
Bohr Model • The orbit where the e- is determines the outer dimensions of the atom. • The energy of the e- increases as it moves into orbits that are farther and farther from the nucleus (excited atom).
Where the electron starts • The energy level an electron starts from is called its ground state.
Changing the energy • Let’s look at a hydrogen atom
Changing the energy • Heat or electricity or light can move the electron up energy levels
Changing the energy • As the electron falls back to ground state it gives the energy back as light
Changing the energy • May fall down in steps • Each with a different energy, frequency, and wavelength
The Bohr Ring Atom n = 4 n = 3 n = 2 n = 1
