Presentation on theme: "Light and the Quantum Mechanical Model of the Atom"— Presentation transcript:
1 Light and the Quantum Mechanical Model of the Atom
2 LightThe study of light led to the development of the quantum mechanical model.Light is a kind of electromagnetic radiation.Electromagnetic radiation includes many kinds of wavesAll move at 3.00x108 m/s or 3.00x1010 cm/s (abbreviated: c)
3 Parts of a waveCrestWavelengthAmplitudeOriginTrough
4 Parts of Wave Origin - the base line of the energy. Crest - high point on a waveTrough - Low point on a waveAmplitude - distance from origin to crestWavelength - distance from crest to crestWavelength - is abbreviated l (Greek letter lambda)
5 FrequencyThe 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
6 Frequency and Wavelength Are inversely relatedAs one goes up the other goes down.Different frequencies of light are different colors of light.There is a wide variety of frequenciesThe whole range is called a spectrum
8 Energy and Frequency E = (h)(n) E is the energy of the photon n is the frequencyh is Planck’s constanth = x Joules*sec.
9 The Math You WILL need to Know for this Chapter Only 2 equations:c = lnE = hnc is always x 108 m/sh is always x J•s
10 ExamplesWhat is the frequency of red light with a wavelength of 4.2 x 10-5 cm?What is the wavelength of The River 105.9, which broadcasts at a frequency of 640 kHz?What is the energy of a photon of each of the above?
11 Atomic Spectra How light & color tells us about atoms
12 White Light It is made up of all the colors of the visible spectrum. Passing it through a prism separates it.This is called a continuous spectrumbecause you see all the colors of the visible spectrum blurred together (ROYGBIV)
13 If the light is not white By heating or electrifying a sample of atoms scientists can get it to give off colors.Passing this light through a prism does something differentYou get colors of light that relate to specific frequencies and therefore specific energiesThis is called …
14 Atomic Emission Spectrum or Line Spectrum Each element gives off a unique set of colors.This info can be used to help identify atoms in substancesEx: stars
18 Changing the energyAdding energy can move the electron up to higher energy levelsThe more energy added, the more energy levels the e- moves
19 As the electron falls back to its original ground state it gives the absorbed energy back as light we can seeThe further the e- fall, the more energy, and the higher the frequency of light.
20 Max Planck 1900 – from Germany Tried to explain why metals changed color the way they did when they are heatedThey only show certain colors, not all the colors in the visible spectrum. WHY?The energy is changed in a specific amount called a quantum
21 Light as a Particle Energy is quantized. These smallest pieces of light are called photons.
23 Light is also a particle it comes in chunks called photons Light is a wave we can measure its wave length and determine its frequency and it behaves as a waveLight is also a particle it comes in chunks called photonsAlbert Einstein came up with this idea
24 Photoelectric EffectMetals eject electrons when light of a specific frequency (called a threshold frequency) shines on them.The light has to have enough energy and if the light is the wrong frequency then it won’t work at all (no matter how bright the light)Uses of this: solar cells, camera flash, & automatic doorsFYI: Explaining this effect is how Einstein won his Nobel Prize
25 More obvious with the very small To measure where a electron is, we use light.But the light moves the electronAnd hitting the electron changes the frequency of the light.
26 Matter is also a Wave BUT… This does not apply to objects bigger than an atom b/c their wavelengths are too smallEx: A baseball has a wavelength of about m when moving 30 m/sAn electron at the same speed has a wavelength of 10-3 cmThis length is big enough to measure.We called these “matter waves”
27 The physics of the very small Quantum mechanics explains how the very small behaves.Quantum mechanics is based on probability because
28 Heisenberg Uncertainty Principle It is impossible to know exactly the speed and position of a particle.The better we know one, the less we know the other.The act of measuring changes the properties.
29 After Before Photon changes wavelength Photon Electron changes velocityMoving Electron