10/27/2017 [pgs ]

Transcription

1 Objectives SWBAT explain the relationship between energy and frequency. SWBAT predict the behavior of and/or calculate quantum and photon energy from frequency. SWBAT explain how the quantization of energy of an atom relates to the electromagnetic (EM) spectrum. SWBAT identify and describe the different aspects and electromagnetic radiation of the EM spectrum. SWBAT use the EM spectrum to calculate wavelength, frequency, and/or energy. SWBAT explain the relationship between energy and frequency; and predict the behavior of and/or calculate quantum and photon energy from frequency. [pgs ] Essential Question How does the emission spectrum of atoms provide insight into the structure of an atom?

2 Bohr studied the light produced when atoms were excited by heat or electricity. Bohr s Model Rutherford's model couldn't explain why unique colors were obtained by atoms of different elements.

3 Bohr s Model Bohr proposed that electrons are in orbits & when excited jump to a higher orbit. When they fall back to the original they give off light. Electrons orbit the nucleus like planets orbit the sun.

4 Bohr s Model Each electron shell can hold a certain number of electrons Electron shells are filled from the inside out Noble Gases have full outer electron shells All other elements have partially filled outer electron shells Shells (Orbits) Maximum # Electrons Allowed 1 st 2e- 2 nd 8e- 3 rd 18e- 4 th 32e-

5 Bohr s Model The electrons in the outermost shell are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell The number of electron shells with electrons is the same as the period number Atoms will try to gain or lose electrons to have a full valence shell The period number is the number you see going down the left side of the periodic table

6 Drawing Bohr Models 1. Draw the nucleus. 2. Write the number of neutrons and the number of protons in the nucleus. 3. Draw the first energy level. 4. Draw the electrons in the energy levels according to the rules below. Make sure you draw the electrons in pairs. 5. Keep track of how many electrons are put in each level and the number of electrons left to use. You must fill one level before going on to draw the next level!

7 Guided Practice 11 Na Protons: Neutrons: Electrons: How many energy shells will this have? 3 How many valence (outer) electrons does this element have? 1 Bohr Model: Sodium

8 Guided Practice 15 P Phosphorous Protons: Neutrons: Electrons: How many energy shells will this have? 3 How many valence (outer) electrons does this element have? 5 Bohr Model:

9 Guided Practice 6 C Protons: Neutrons: Electrons: How many energy shells will this have? 2 How many valence (outer) electrons does this element have? 4 Bohr Model: Carbon

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11 Bell Ringer Mathematics teaches us lessons on how to rearrange equations to solve for single variables. For the following equations rearrange the equation to solve for the unknown variable. 3x + 5 = 11 2y = 4y (m + 5) = 16

12 MODELS OF LIGHT LIGHT IS A WAVE So which one is right? LIGHT IS A PARTICLE They are both right...and they are both wrong. That s called W A V E - P A R T I C L E duality In some experiments, the wave model works best. In other experiments, the particle model works best. Thus, we use both.

13 Light is a WAVE Propagating wave of oscillating electric and magnetic fields Described by wavelength,, and frequency, f. F = v where v is the speed of the wave. In a vacuum, v = c = 3.00 x 10 8 m/s. Synonyms for light Electromagnetic wave Electromagnetic radiation Radiation Visible light is light that our eyes are sensitive to; however, that is not the only type of electromagnetic radiation

14 Wavelength vs. Frequency Wavelength ( ) the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave. Frequency (f) the rate at which a vibration occurs that constitutes a wave, either in a material (as in sound waves), or in an electromagnetic field (as in radio waves and light), usually measured per second. Inverse Relationship

15 Light comes in many wavelengths When white light passes through a glass prism (or a diffraction grating), it separates into colors. These colors have different wavelengths. This group of wavelengths is the visible part of the electromagnetic spectrum. When you see the entire spectrum with no thin dark bands, it is a continuous spectrum.

16 Electromagnetic Spectrum

17 Check for Understanding 1. What is the wavelength range for the visible light spectrum? 2. Which color of light has a longer wavelength purple or red? 3. Suppose that a certain medical treatment requires exposing certain tissues to high frequency radiation. Would that radiation likely be gamma rays or radio waves?

18 Light is a PARTICLE Albert Einstein proposed that light consisted of photons. A photon is a particle or packet of energy. A photon has an energy of E=hf where h is called Planck s constant and f is frequency. High frequency (low wavelength) photons have high energy; low frequency (high wavelength) photons have low energy.

19 How is light absorbed and emitted by atoms in interstellar gases or stars?

20 Bohr Model The Bohr model is a planetary model, where the electron orbits the nucleus like a planet orbits the Sun. An electron is only allowed in DISCRETE orbits (n=1, n=2, n=3, etc.) The higher the orbit, the higher the energy of the electron.

21 Modern View of Hydrogen Now, we know that the electron has discrete energy levels, but it does not orbit the nucleus at fixed distances from the nucleus. In fact, it may be found anywhere in certain allowed regions called orbitals. Each orbital corresponds to a certain energy of the electron.

22 Absorption, Emission, and Energy photon Absorption Emission photon When an atom absorbs a photon, it gains energy. When an atom loses energy, it emits a photon. An atom can only absorb photons or emit photons of specific energy. Those right energies correspond to the DIFFERENCES in energy between the allowed energy levels.

23 Absorption Spectrum If light of a continuous spectrum is incident on a gas of hydrogen atoms, then electrons will absorb some of the light. As a result, bands of the spectrum are missing; these are called absorption lines. By the way, these same atoms emit the same colors in an emission spectrum!

24 Emission Spectrum If excited hydrogen atoms fall to lower energy states, photons will be emitted. The emitted photons will be detected as light of certain bands of frequencies (i.e. colors). The collection of bands (or lines) forms an emission spectrum.

25 CALCULATIONS BETWEEN WAVELENGTH, FREQUENCY AND ENERGY Wavelength ( ): the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave. Speed of Light (c): the distance light can travel in a unit of time through a given substance. Frequency (f): the rate at which a vibration occurs that constitutes a wave, either in a material (as in sound waves), or in an electromagnetic field (as in radio waves and light), usually measured per second.

26 Check for Understanding Speed of light = 3.00 x 10 8 m/s = λ v Find Frequency (v) using the equation c A gamma ray has a wavelength of nm. What is the frequency of the wave? λ Find Wavelength ( ) using the equation What is the wavelength of an X ray that has a frequency of 7.8 X Hz? c v