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Chapter Two Chapter Two …continued Electrons in Atoms.

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Presentation on theme: "Chapter Two Chapter Two …continued Electrons in Atoms."— Presentation transcript:

1 Chapter Two Chapter Two …continued Electrons in Atoms

2 Bohrs Model l Why dont the electrons fall into the nucleus? - Move like planets around the sun. - Circular orbits at different levels. - Amounts of energy separate one level from another.

3 Bohrs Model Nucleus Electron Orbit Energy Levels

4 Bohrs Model Increasing energy Nucleus First Second Third Fourth Fifth } l Further away from the nucleus means higher energy. l There is no in between energy l Energy Levels

5 l The atom is found inside a blurry electron cloud - area where there is a chance of finding an electron. The Quantum Mechanical Model

6 Evidence of Quantum Mechanical Model l The study of light led to the development of the quantum mechanical model. l Light is a kind of electromagnetic radiation. l Electromagnetic radiation includes many kinds of waves l All move at 3.00 x 10 8 m/s ( c)

7 Parts of a wave Wavelength Amplitude Orgin Crest Trough

8 Parts of Wave l Orgin - the base line of the energy. l Crest - high point on a wave l Trough - Low point on a wave l Amplitude - distance from origin to crest l Wavelength - distance from crest to crest –abbreviated Greek letter lambda).

9 Frequency l The number of waves that pass a given point per second. l Units are cycles/sec, or hertz (hz) Abbreviated the Greek letter nu c =

10 Frequency and wavelength l Are inversely related l As one goes up, the other goes down. l Different frequencies of light are different colors of light. l Wide variety of frequencies l The whole range is called a spectrum

11 Radio waves Micro waves Infrared. Ultra- violet X- Rays Gamma Rays Low Frequency High Frequency Long Wavelength Short Wavelength Visible Light Low Energy High Energy

12 Atomic Spectrum How color tells us about atoms

13 Prism l White light is made up of all the colors of the visible spectrum. l Passing it through a prism separates it.

14 If the light is not white l By heating a gas with electricity we can get it to give off colors. l Passing this light through a prism does something different...

15 Atomic Spectrum l Each element gives off its own characteristic colors. l Can be used to identify the atom. l Composition of stars.

16 These are called discontinuous spectra, or line spectra unique to each element. Light is given off, or emitted. Emission Spectra

17 Energy and frequency (Honors) E = hn l E is the energy of the photon n is the frequency l h is Plancks constant - h = 6.6262 x 10 -34 Joules sec. l Joule is the metric unit of Energy

18 Equations for Light Only 2 equations c = ln E = h n Plug and chug.

19 Examples l What is the wavelength of blue light with a frequency of 8.3 x 10 15 hz? l What is the frequency of red light with a wavelength of 4.2 x 10 -5 m? l What is the energy of a photon of each of the above?

20 An Explanation of Atomic Spectra

21 Where the Electron Starts l The energy level an electron starts from is called its ground state.

22 Changing the energy l Lets look at a hydrogen atom

23 Changing the energy l Heat, electricity, or light can move the electron up energy levels

24 Changing the energy l As the electron falls back to ground state it gives the energy back as light

25 l May fall down in steps l Each with a different energy Changing the energy

26 { { {

27 l Further they fall, more energy, higher frequency. l This is simplified l the orbitals also have different energies inside energy levels l All the electrons can move around. Ultraviolet Visible Infrared

28 Heisenberg Uncertainty Principle l It is impossible to know exactly the speed and velocity of a particle. l The better we know one, the less we know the other. l The act of measuring changes the properties.

29 More obvious with the very small l To measure where a electron is, we use light. l But the light moves the electron l And hitting the electron changes the frequency of the light.

30 Moving Electron Photon Before Electron Changes velocity Photon changes wavelength After

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